//===--- NameLookup.cpp - Swift Name Lookup Routines ----------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file implements interfaces for performing name lookup.
//
//===----------------------------------------------------------------------===//

#include "swift/AST/NameLookup.h"
#include "swift/AST/ASTContext.h"
#include "swift/AST/ASTVisitor.h"
#include "swift/AST/ASTWalker.h"
#include "swift/AST/ClangModuleLoader.h"
#include "swift/AST/ConformanceAttributes.h"
#include "swift/AST/DebuggerClient.h"
#include "swift/AST/ExistentialLayout.h"
#include "swift/AST/GenericParamList.h"
#include "swift/AST/GenericSignature.h"
#include "swift/AST/ImportCache.h"
#include "swift/AST/Initializer.h"
#include "swift/AST/LazyResolver.h"
#include "swift/AST/MacroDeclaration.h"
#include "swift/AST/ModuleNameLookup.h"
#include "swift/AST/NameLookupRequests.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/PotentialMacroExpansions.h"
#include "swift/AST/PropertyWrappers.h"
#include "swift/AST/SourceFile.h"
#include "swift/AST/TypeCheckRequests.h"
#include "swift/Basic/Assertions.h"
#include "swift/Basic/Debug.h"
#include "swift/Basic/STLExtras.h"
#include "swift/Basic/SourceManager.h"
#include "swift/Basic/Statistic.h"
#include "swift/ClangImporter/ClangImporterRequests.h"
#include "swift/ClangImporter/ClangModule.h"
#include "swift/Parse/Lexer.h"
#include "swift/Strings.h"
#include "clang/AST/DeclObjC.h"
#include "clang/Basic/Specifiers.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

#include <deque>

#define DEBUG_TYPE "namelookup"

using namespace swift;
using namespace swift::namelookup;

void VisibleDeclConsumer::anchor() {}
void VectorDeclConsumer::anchor() {}

ValueDecl *LookupResultEntry::getBaseDecl() const {
  if (BaseDC == nullptr)
    return nullptr;

  return BaseDecl;
}

void LookupResult::filter(
    llvm::function_ref<bool(LookupResultEntry, bool)> pred) {
  size_t index = 0;
  size_t originalFirstOuter = IndexOfFirstOuterResult;
  Results.erase(std::remove_if(Results.begin(), Results.end(),
                               [&](LookupResultEntry result) -> bool {
                                 auto isInner = index < originalFirstOuter;
                                 ++index;
                                 if (pred(result, !isInner))
                                   return false;

                                 // Need to remove this, which means, if it is
                                 // an inner result, the outer results need to
                                 // shift down.
                                 if (isInner)
                                   --IndexOfFirstOuterResult;
                                 return true;
                               }),
                Results.end());
}

void LookupResult::shiftDownResults() {
  // Remove inner results.
  Results.erase(Results.begin(), Results.begin() + IndexOfFirstOuterResult);
  IndexOfFirstOuterResult = 0;

  if (Results.empty())
    return;

  // Compute IndexOfFirstOuterResult.
  const DeclContext *dcInner = Results.front().getValueDecl()->getDeclContext();
  for (auto &&result : Results) {
    const DeclContext *dc = result.getValueDecl()->getDeclContext();
    if (dc == dcInner ||
        (dc->isModuleScopeContext() && dcInner->isModuleScopeContext()))
      ++IndexOfFirstOuterResult;
    else
      break;
  }
}

void swift::simple_display(llvm::raw_ostream &out,
                           UnqualifiedLookupOptions options) {
  using Flag = std::pair<UnqualifiedLookupFlags, StringRef>;
  Flag possibleFlags[] = {
      {UnqualifiedLookupFlags::AllowProtocolMembers, "AllowProtocolMembers"},
      {UnqualifiedLookupFlags::IgnoreAccessControl, "IgnoreAccessControl"},
      {UnqualifiedLookupFlags::IncludeOuterResults, "IncludeOuterResults"},
      {UnqualifiedLookupFlags::TypeLookup, "TypeLookup"},
      {UnqualifiedLookupFlags::MacroLookup, "MacroLookup"},
      {UnqualifiedLookupFlags::ModuleLookup, "ModuleLookup"},
      {UnqualifiedLookupFlags::DisregardSelfBounds, "DisregardSelfBounds"},
      {UnqualifiedLookupFlags::IgnoreMissingImports, "IgnoreMissingImports"},
      {UnqualifiedLookupFlags::ABIProviding, "ABIProviding"},
  };

  auto flagsToPrint = llvm::make_filter_range(
      possibleFlags, [&](Flag flag) { return options.contains(flag.first); });

  out << "{ ";
  interleave(
      flagsToPrint, [&](Flag flag) { out << flag.second; },
      [&] { out << ", "; });
  out << " }";
}

void DebuggerClient::anchor() {}

void AccessFilteringDeclConsumer::foundDecl(
    ValueDecl *D, DeclVisibilityKind reason,
    DynamicLookupInfo dynamicLookupInfo) {
  if (!D->isAccessibleFrom(DC))
    return;

  ChainedConsumer.foundDecl(D, reason, dynamicLookupInfo);
}

void UsableFilteringDeclConsumer::foundDecl(
    ValueDecl *D, DeclVisibilityKind reason,
    DynamicLookupInfo dynamicLookupInfo) {
  switch (reason) {
  case DeclVisibilityKind::LocalDecl:
  case DeclVisibilityKind::FunctionParameter:
    // A type context cannot close over variables defined in outer type
    // contexts.
    if (isa<VarDecl>(D) &&
        D->getDeclContext()->getInnermostTypeContext() != typeContext) {
      return;
    }
    break;

  case DeclVisibilityKind::MemberOfOutsideNominal:
  case DeclVisibilityKind::MemberOfCurrentNominal:
  case DeclVisibilityKind::MemberOfSuper:
  case DeclVisibilityKind::MemberOfProtocolConformedToByCurrentNominal:
  case DeclVisibilityKind::MemberOfProtocolDerivedByCurrentNominal:
  case DeclVisibilityKind::DynamicLookup:
    // Members on 'Self' including inherited/derived ones are always usable.
    break;

  case DeclVisibilityKind::GenericParameter:
    // Generic params are type decls and are always usable from nested context.
    break;

  case DeclVisibilityKind::VisibleAtTopLevel: {
    // Skip when Loc is within the decl's own initializer. We only need to do
    // this for top-level decls since local decls are already excluded from
    // their own initializer by virtue of the ASTScope lookup.
    if (auto *VD = dyn_cast<VarDecl>(D)) {
      // Only check if the VarDecl has the same (or parent) context to avoid
      // grabbing the end location for every decl with an initializer
      if (auto *init = VD->getParentInitializer()) {
        auto *varContext = VD->getDeclContext();
        if (DC == varContext || DC->isChildContextOf(varContext)) {
          auto initRange = Lexer::getCharSourceRangeFromSourceRange(
              SM, init->getSourceRange());
          if (initRange.isValid() && initRange.contains(Loc))
            return;
        }
      }
    }
    break;
  }
  }

  // Filter out shadowed decls. Do this for only usable values even though
  // unusable values actually can shadow outer values, because compilers might
  // be able to diagnose it with fix-it to add the qualification. E.g.
  //   func foo(global: T) {}
  //   struct Outer {
  //     func foo(outer: T) {}
  //     func test() {
  //       struct Inner {
  //         func test() {
  //           <HERE>
  //         }
  //       }
  //     }
  //   }
  // In this case 'foo(global:)' is shadowed by 'foo(outer:)', but 'foo(outer:)'
  // is _not_ usable because it's outside the current type context, whereas
  // 'foo(global:)' is still usable with 'ModuleName.' qualification.
  // FIXME: (for code completion,) If a global value or a static type member is
  // shadowd, we should suggest it with prefix (e.g. 'ModuleName.value').
  auto inserted = SeenNames.insert({D->getBaseName(), {D, reason}});
  if (!inserted.second) {
    auto shadowingReason = inserted.first->second.second;
    auto *shadowingD = inserted.first->second.first;

    // A type decl cannot have overloads, and shadows everything outside the
    // scope.
    if (isa<TypeDecl>(shadowingD))
      return;

    switch (shadowingReason) {
    case DeclVisibilityKind::LocalDecl:
    case DeclVisibilityKind::FunctionParameter:
      // Local func and var/let with a conflicting name.
      //   func foo() {
      //     func value(arg: Int) {}
      //     var value = ""
      //   }
      // In this case, 'var value' wins, regardless of their source order.
      // So, for confilicting local values in the same decl context, even if the
      // 'var value' is reported after 'func value', don't shadow it, but we
      // shadow everything with the name after that.
      if (reason == DeclVisibilityKind::LocalDecl &&
          isa<VarDecl>(D) && !isa<VarDecl>(shadowingD) &&
          shadowingD->getDeclContext() == D->getDeclContext()) {
        // Replace the shadowing decl so we shadow subsequent conflicting decls.
        inserted.first->second = {D, reason};
        break;
      }

      // Otherwise, a local value shadows everything outside the scope.
      return;

    case DeclVisibilityKind::GenericParameter:
      // A Generic parameter is a type name. It shadows everything outside the
      // generic context.
      return;

    case DeclVisibilityKind::MemberOfCurrentNominal:
    case DeclVisibilityKind::MemberOfSuper:
    case DeclVisibilityKind::MemberOfProtocolConformedToByCurrentNominal:
    case DeclVisibilityKind::MemberOfProtocolDerivedByCurrentNominal:
    case DeclVisibilityKind::DynamicLookup:
      switch (reason) {
      case DeclVisibilityKind::MemberOfCurrentNominal:
      case DeclVisibilityKind::MemberOfSuper:
      case DeclVisibilityKind::MemberOfProtocolConformedToByCurrentNominal:
      case DeclVisibilityKind::MemberOfProtocolDerivedByCurrentNominal:
      case DeclVisibilityKind::DynamicLookup:
        // Members on the current type context don't shadow members with the
        // same base name on the current type contxt. They are overloads.
        break;
      default:
        // Members of a type context shadows values/types outside.
        return;
      }
      break;

    case DeclVisibilityKind::MemberOfOutsideNominal:
      // For static values, it's unclear _which_ type context (i.e. this type,
      // super classes, conforming protocols) this decl was found in. For now,
      // consider all the outer nominals are the same.

      if (reason == DeclVisibilityKind::MemberOfOutsideNominal)
        break;

      // Values outside the nominal are shadowed.
      return;

    case DeclVisibilityKind::VisibleAtTopLevel:
      // Top level decls don't shadow anything.
      // Well, that's not true. Decls in the current module shadows decls in
      // the imported modules. But we don't care them here.
      break;
    }
  }

  ChainedConsumer.foundDecl(D, reason, dynamicLookupInfo);
}

void LookupResultEntry::print(llvm::raw_ostream& out) const {
  getValueDecl()->print(out);
  if (auto dc = getBaseDecl()) {
    out << "\nbase: ";
    dc->print(out);
    out << "\n";
  } else
    out << "\n(no-base)\n";

  auto abiRole = ABIRoleInfo(getValueDecl());
  out << "provides API=" << abiRole.providesAPI()
      << ", provides ABI=" << abiRole.providesABI() << "\n";
}


bool swift::removeOverriddenDecls(SmallVectorImpl<ValueDecl*> &decls) {
  if (decls.size() < 2)
    return false;

  llvm::SmallPtrSet<ValueDecl*, 8> overridden;
  for (auto decl : decls) {
    // Don't look at the overrides of operators in protocols. The global
    // lookup of operators means that we can find overriding operators that
    // aren't relevant to the types in hand, and will fail to type check.
    if (isa<ProtocolDecl>(decl->getDeclContext())) {
      if (auto func = dyn_cast<FuncDecl>(decl))
        if (func->isOperator())
          continue;
    }

    while (auto overrides = decl->getOverriddenDecl()) {
      if (!overridden.insert(overrides).second) {
        // If we've already seen a decl then there's no need to visit the decls
        // that it overrides since they should already be in the set. This also
        // prevents infinite loops in the case that the AST contains an
        // override chain with a cycle due to circular inheritance.
        break;
      }

      DEBUG_ASSERT(decl != overrides && "Circular class inheritance?");
      decl = overrides;
    }
  }

  // If no methods were overridden, we're done.
  if (overridden.empty()) return false;

  // Erase any overridden declarations
  bool anyOverridden = false;
  decls.erase(std::remove_if(decls.begin(), decls.end(),
                             [&](ValueDecl *decl) -> bool {
                               if (overridden.count(decl) > 0) {
                                 anyOverridden = true;
                                 return true;
                               }

                               return false;
                             }),
              decls.end());

  return anyOverridden;
}

enum class ConstructorComparison {
  Worse,
  Same,
  Better,
};

bool swift::removeOutOfModuleDecls(SmallVectorImpl<ValueDecl*> &decls,
                                   Identifier moduleSelector,
                                   const DeclContext *dc) {
  if (moduleSelector.empty())
    return false;

  ASTContext &ctx = dc->getASTContext();

  // FIXME: Should we look this up relative to dc?
  // We'd need a new ResolutionKind.
  // FIXME: How can we diagnose this?
  ModuleDecl *visibleFromRoot = ctx.getLoadedModule(moduleSelector);
  if (!visibleFromRoot && moduleSelector == ctx.TheBuiltinModule->getName())
    visibleFromRoot = ctx.TheBuiltinModule;
  if (!visibleFromRoot) {
    LLVM_DEBUG(llvm::dbgs() << "no module " << moduleSelector << "\n");
    bool clearedAny = !decls.empty();
    decls.clear();
    return clearedAny;
  }

  SmallVector<ModuleDecl *, 4> visibleFrom;
  dc->getSeparatelyImportedOverlays(visibleFromRoot, visibleFrom);
  if (visibleFrom.empty())
    visibleFrom.push_back(visibleFromRoot);

  size_t initialCount = decls.size();
  decls.erase(
    std::remove_if(decls.begin(), decls.end(), [&](ValueDecl *decl) -> bool {
      bool inScope = llvm::any_of(visibleFrom, [&](ModuleDecl *visibleFromMod) {
        return ctx.getImportCache().isImportedBy(decl->getModuleContext(),
                                                 visibleFromMod);
      });

      LLVM_DEBUG(decl->dumpRef(llvm::dbgs()));
      LLVM_DEBUG(llvm::dbgs() << ": " << decl->getModuleContext()->getName()
                              << (inScope ? " is " : " is NOT ")
                              << "selected by " << moduleSelector << "\n");

      return !inScope;
    }),
    decls.end());
  return initialCount != decls.size();
}

/// Determines whether \p ctor1 is a "better" initializer than \p ctor2.
static ConstructorComparison compareConstructors(ConstructorDecl *ctor1,
                                                 ConstructorDecl *ctor2,
                                                 const swift::ASTContext &ctx) {
  bool available1 = !ctor1->isUnavailable();
  bool available2 = !ctor2->isUnavailable();

  // An unavailable initializer is always worse than an available initializer.
  if (available1 < available2)
    return ConstructorComparison::Worse;

  if (available1 > available2)
    return ConstructorComparison::Better;

  CtorInitializerKind kind1 = ctor1->getInitKind();
  CtorInitializerKind kind2 = ctor2->getInitKind();

  if (kind1 > kind2)
    return ConstructorComparison::Worse;

  if (kind1 < kind2)
    return ConstructorComparison::Better;

  return ConstructorComparison::Same;
}

static bool isMemberImplementation(ValueDecl *VD) {
  return VD->isObjCMemberImplementation();
}
static bool isMemberImplementation(OperatorDecl *VD) {
  return false;
}
static bool isMemberImplementation(PrecedenceGroupDecl *VD) {
  return false;
}

/// Given a set of declarations whose names and interface types have matched,
/// figure out which of these declarations have been shadowed by others.
template <typename T>
static void recordShadowedDeclsAfterTypeMatch(
                              ArrayRef<T> decls,
                              const DeclContext *dc,
                              llvm::SmallPtrSetImpl<T> &shadowed) {
  assert(decls.size() > 1 && "Nothing collided");

  // Compare each declaration to every other declaration. This is
  // unavoidably O(n^2) in the number of declarations, but because they
  // all have the same signature, we expect n to remain small.
  auto *curModule = dc->getParentModule();
  ASTContext &ctx = curModule->getASTContext();
  auto &imports = ctx.getImportCache();

  for (unsigned firstIdx : indices(decls)) {
    auto firstDecl = decls[firstIdx];
    auto firstModule = firstDecl->getModuleContext();
    auto firstDC = firstDecl->getDeclContext();
    bool firstTopLevel = firstDC->isModuleScopeContext();

    auto name = firstDecl->getBaseName();

    auto isShadowed = [&](ArrayRef<ImportPath::Access> paths) {
      for (auto path : paths) {
        if (path.matches(name))
          return false;
      }

      return true;
    };

    auto isScopedImport = [&](ArrayRef<ImportPath::Access> paths) {
      for (auto path : paths) {
        if (path.empty())
          continue;
        if (path.matches(name))
          return true;
      }

      return false;
    };

    auto isPrivateImport = [&](ModuleDecl *module) {
      auto file = dc->getParentSourceFile();
      if (!file) return false;
      for (const auto &import : file->getImports()) {
        if (import.options.contains(ImportFlags::PrivateImport)
            && import.module.importedModule == module
            && import.module.accessPath.matches(name))
          return true;
      }
      return false;
    };

    bool firstPrivate = isPrivateImport(firstModule);

    for (unsigned secondIdx : range(firstIdx + 1, decls.size())) {
      // Determine whether one module takes precedence over another.
      auto secondDecl = decls[secondIdx];
      auto secondModule = secondDecl->getModuleContext();
      auto secondDC = secondDecl->getDeclContext();
      bool secondTopLevel = secondDC->isModuleScopeContext();
      bool secondPrivate = isPrivateImport(secondModule);

      // For member types, we skip most of the below rules. Instead, we allow
      // member types defined in a subclass to shadow member types defined in
      // a superclass.
      if (isa<TypeDecl>(firstDecl) &&
          isa<TypeDecl>(secondDecl) &&
          !firstTopLevel &&
          !secondTopLevel) {
        auto *firstClass = firstDecl->getDeclContext()->getSelfClassDecl();
        auto *secondClass = secondDecl->getDeclContext()->getSelfClassDecl();
        if (firstClass && secondClass && firstClass != secondClass) {
          if (firstClass->isSuperclassOf(secondClass)) {
            shadowed.insert(firstDecl);
            continue;
          } else if (secondClass->isSuperclassOf(firstClass)) {
            shadowed.insert(secondDecl);
            continue;
          }
        }

        // If one declaration is in a protocol or extension thereof and the
        // other is not, prefer the one that is not.
        if ((bool)firstDecl->getDeclContext()->getSelfProtocolDecl() !=
              (bool)secondDecl->getDeclContext()->getSelfProtocolDecl()) {
          if (firstDecl->getDeclContext()->getSelfProtocolDecl()) {
            shadowed.insert(firstDecl);
            break;
          } else {
            shadowed.insert(secondDecl);
            continue;
          }
        }

        continue;
      }

      // Top-level type declarations in a module shadow other declarations
      // visible through the module's imports.
      //
      // [Backward compatibility] Note that members of types have the same
      // shadowing check, but we do it after dropping unavailable members.
      if (firstModule != secondModule &&
          firstTopLevel && secondTopLevel) {
        auto firstPaths = imports.getAllAccessPathsNotShadowedBy(
          firstModule, secondModule, dc);
        auto secondPaths = imports.getAllAccessPathsNotShadowedBy(
          secondModule, firstModule, dc);

        // Check if one module shadows the other.
        if (isShadowed(firstPaths)) {
          shadowed.insert(firstDecl);
          break;
        } else if (isShadowed(secondPaths)) {
          shadowed.insert(secondDecl);
          continue;
        }

        // If neither module shadows the other, but one was imported with
        // '@_private import' in dc, we want to favor that module. This makes
        // name lookup in this file behave more like name lookup in the file we
        // imported from, avoiding headaches for source-transforming tools.
        if (!firstPrivate && secondPrivate) {
          shadowed.insert(firstDecl);
          break;
        } else if (firstPrivate && !secondPrivate) {
          shadowed.insert(secondDecl);
          continue;
        }

        // We might be in a situation where neither module shadows the
        // other, but one declaration is visible via a scoped import.
        bool firstScoped = isScopedImport(firstPaths);
        bool secondScoped = isScopedImport(secondPaths);
        if (!firstScoped && secondScoped) {
          shadowed.insert(firstDecl);
          break;
        } else if (firstScoped && !secondScoped) {
          shadowed.insert(secondDecl);
          continue;
        }
      }

      // Member implementations are usually filtered out by access control.
      // They're sometimes visible in contexts that can directly access storage,
      // though, and there they should shadow the matching imported declaration.
      if (firstDC != secondDC
            && firstDC->getImplementedObjCContext() ==
                 secondDC->getImplementedObjCContext()) {
        if (isMemberImplementation(firstDecl) && secondDecl->hasClangNode()) {
          shadowed.insert(secondDecl);
          continue;
        }
        if (isMemberImplementation(secondDecl) && firstDecl->hasClangNode()) {
          shadowed.insert(firstDecl);
          continue;
        }
      }

      // Swift 4 compatibility hack: Don't shadow properties defined in
      // extensions of generic types with properties defined elsewhere.
      // This is due to the fact that in Swift 4, we only gave custom overload
      // types to properties in extensions of generic types, otherwise we
      // used the null type.
      if (!ctx.isSwiftVersionAtLeast(5) && isa<ValueDecl>(firstDecl)) {
        auto secondSig = cast<ValueDecl>(secondDecl)->getOverloadSignature();
        auto firstSig = cast<ValueDecl>(firstDecl)->getOverloadSignature();
        if (firstSig.IsVariable && secondSig.IsVariable)
          if (firstSig.InExtensionOfGenericType !=
              secondSig.InExtensionOfGenericType)
            continue;
      }

      // If one declaration is in a protocol or extension thereof and the
      // other is not, prefer the one that is not.
      if ((bool)firstDecl->getDeclContext()->getSelfProtocolDecl() !=
            (bool)secondDecl->getDeclContext()->getSelfProtocolDecl()) {
        if (firstDecl->getDeclContext()->getSelfProtocolDecl()) {
          shadowed.insert(firstDecl);
          break;
        } else {
          shadowed.insert(secondDecl);
          continue;
        }
      }

      // If one declaration is available and the other is not, prefer the
      // available one.
      if (firstDecl->isUnavailable() != secondDecl->isUnavailable()) {
        if (firstDecl->isUnavailable()) {
          shadowed.insert(firstDecl);
          break;
        } else {
          shadowed.insert(secondDecl);
          continue;
        }
      }

      // Don't apply module-shadowing rules to members of protocol types.
      if (isa<ProtocolDecl>(firstDecl->getDeclContext()) ||
          isa<ProtocolDecl>(secondDecl->getDeclContext()))
        continue;

      // [Backward compatibility] For members of types, the general module
      // shadowing check is performed after unavailable candidates have
      // already been dropped.
      if (firstModule != secondModule &&
          !firstTopLevel && !secondTopLevel) {
        auto firstPaths = imports.getAllAccessPathsNotShadowedBy(
          firstModule, secondModule, dc);
        auto secondPaths = imports.getAllAccessPathsNotShadowedBy(
          secondModule, firstModule, dc);

        // Check if one module shadows the other.
        if (isShadowed(firstPaths)) {
          shadowed.insert(firstDecl);
          break;
        } else if (isShadowed(secondPaths)) {
          shadowed.insert(secondDecl);
          continue;
        }
      }

      // Prefer declarations in the any module over those in the standard
      // library module.
      if (auto swiftModule = ctx.getStdlibModule()) {
        if ((firstModule == swiftModule) != (secondModule == swiftModule)) {
          // If the second module is the standard library module, the second
          // declaration is shadowed by the first.
          if (secondModule == swiftModule) {
            shadowed.insert(secondDecl);
            continue;
          }

          // Otherwise, the first declaration is shadowed by the second. There is
          // no point in continuing to compare the first declaration to others.
          shadowed.insert(firstDecl);
          break;
        }
      }

      // Next, prefer any other module over the _Concurrency module.
      if (auto concurModule = ctx.getLoadedModule(ctx.Id_Concurrency)) {
        if ((firstModule == concurModule) != (secondModule == concurModule)) {
          // If second module is _Concurrency, then it is shadowed by first.
          if (secondModule == concurModule) {
            shadowed.insert(secondDecl);
            continue;
          }

          // Otherwise, the first declaration is shadowed by the second.
          shadowed.insert(firstDecl);
          break;
        }
      }

      // Next, prefer any other module over the _StringProcessing module.
      if (auto spModule = ctx.getLoadedModule(ctx.Id_StringProcessing)) {
        if ((firstModule == spModule) != (secondModule == spModule)) {
          // If second module is _StringProcessing, then it is shadowed by
          // first.
          if (secondModule == spModule) {
            shadowed.insert(secondDecl);
            continue;
          }

          // Otherwise, the first declaration is shadowed by the second.
          shadowed.insert(firstDecl);
          break;
        }
      }

      // Next, prefer any other module over the Observation module.
      if (auto obsModule = ctx.getLoadedModule(ctx.Id_Observation)) {
        if ((firstModule == obsModule) != (secondModule == obsModule)) {
          // If second module is (_)Observation, then it is shadowed by
          // first.
          if (secondModule == obsModule) {
            shadowed.insert(secondDecl);
            continue;
          }

          // Otherwise, the first declaration is shadowed by the second.
          shadowed.insert(firstDecl);
          break;
        }
      }

      // The Foundation overlay introduced Data.withUnsafeBytes, which is
      // treated as being ambiguous with SwiftNIO's Data.withUnsafeBytes
      // extension. Apply a special-case name shadowing rule to use the
      // latter rather than the former, which be the consequence of a more
      // significant change to name shadowing in the future.
      if (auto owningStruct1
            = firstDecl->getDeclContext()->getSelfStructDecl()) {
        if (auto owningStruct2
              = secondDecl->getDeclContext()->getSelfStructDecl()) {
          if (owningStruct1 == owningStruct2 &&
              owningStruct1->getName().is("Data") &&
              isa<FuncDecl>(firstDecl) && isa<FuncDecl>(secondDecl) &&
              firstDecl->getName() == secondDecl->getName() &&
              firstDecl->getBaseName().userFacingName() == "withUnsafeBytes") {
            // If the second module is the Foundation module and the first
            // is the NIOFoundationCompat module, the second is shadowed by the
            // first.
            if (firstDecl->getModuleContext()->getName()
                  .is("NIOFoundationCompat") &&
                secondDecl->getModuleContext()->getName().is("Foundation")) {
              shadowed.insert(secondDecl);
              continue;
            }

            // If it's the other way around, the first declaration is shadowed
            // by the second.
            if (secondDecl->getModuleContext()->getName()
                  .is("NIOFoundationCompat") &&
                firstDecl->getModuleContext()->getName().is("Foundation")) {
              shadowed.insert(firstDecl);
              break;
            }
          }
        }
      }

      // Prefer declarations in an overlay to similar declarations in
      // the Clang module it customizes.
      if (firstDecl->hasClangNode() != secondDecl->hasClangNode()) {
        auto clangLoader = ctx.getClangModuleLoader();
        if (!clangLoader) continue;

        if (clangLoader->isInOverlayModuleForImportedModule(
                                              firstDecl->getDeclContext(),
                                              secondDecl->getDeclContext())) {
          shadowed.insert(secondDecl);
          continue;
        }

        if (clangLoader->isInOverlayModuleForImportedModule(
                                               secondDecl->getDeclContext(),
                                               firstDecl->getDeclContext())) {
          shadowed.insert(firstDecl);
          break;
        }
      }
    }
  }
}

/// Return an extended info for a function types that removes the use of
/// the thrown error type, if present.
///
/// Returns \c None when no adjustment is needed.
static std::optional<ASTExtInfo>
extInfoRemovingThrownError(AnyFunctionType *fnType) {
  if (!fnType->hasExtInfo())
    return std::nullopt;

  auto extInfo = fnType->getExtInfo();
  if (!extInfo.isThrowing() || !extInfo.getThrownError())
    return std::nullopt;

  return extInfo.withThrows(true, Type());
}

/// Remove the thrown error type.
static CanType removeThrownError(Type type) {
  return type.transformRec([](TypeBase *type) -> std::optional<Type> {
    if (auto funcTy = dyn_cast<FunctionType>(type)) {
      if (auto newExtInfo = extInfoRemovingThrownError(funcTy)) {
        return FunctionType::get(
                  funcTy->getParams(), funcTy->getResult(), *newExtInfo)
          ->getCanonicalType();
      }

      return std::nullopt;
    }

    if (auto genericFuncTy = dyn_cast<GenericFunctionType>(type)) {
      if (auto newExtInfo = extInfoRemovingThrownError(genericFuncTy)) {
        return GenericFunctionType::get(
                  genericFuncTy->getGenericSignature(),
                  genericFuncTy->getParams(), genericFuncTy->getResult(),
                  *newExtInfo)
          ->getCanonicalType();
      }

      return std::nullopt;
    }

    return std::nullopt;
  })->getCanonicalType();
}

/// Given a set of declarations whose names and generic signatures have matched,
/// figure out which of these declarations have been shadowed by others.
static void recordShadowedDeclsAfterSignatureMatch(
                              ArrayRef<ValueDecl *> decls,
                              const DeclContext *dc,
                              llvm::SmallPtrSetImpl<ValueDecl *> &shadowed) {
  assert(decls.size() > 1 && "Nothing collided");

  // Categorize all of the declarations based on their overload types.
  llvm::SmallDenseMap<CanType, llvm::TinyPtrVector<ValueDecl *>> collisions;
  llvm::SmallVector<CanType, 2> collisionTypes;

  for (auto decl : decls) {
    assert(!isa<TypeDecl>(decl));

    CanType type;

    // FIXME: The type of a variable or subscript doesn't include
    // enough context to distinguish entities from different
    // constrained extensions, so use the overload signature's
    // type. This is layering a partial fix upon a total hack.
    if (auto asd = dyn_cast<AbstractStorageDecl>(decl))
      type = asd->getOverloadSignatureType();
    else
      type = removeThrownError(decl->getInterfaceType()->getCanonicalType());

    // Strip `@Sendable` annotations for declarations that come from
    // or are exposed to Objective-C to make it possible to introduce
    // new annotations without breaking shadowing rules.
    //
    // This is a narrow fix for specific backwards-incompatible cases
    // we know about, it could be extended to use `isObjC()` in the
    // future if we find problematic cases were a more general change
    // is required.
    if (decl->hasClangNode() || decl->getAttrs().hasAttribute<ObjCAttr>()) {
      type =
          type->stripConcurrency(/*recursive=*/true, /*dropGlobalActor=*/false)
              ->getCanonicalType();
    }

    // Record this declaration based on its signature.
    auto &known = collisions[type];
    if (known.size() == 1) {
      collisionTypes.push_back(type);
    }
    known.push_back(decl);
  }

  // Check whether we have shadowing for signature collisions.
  for (auto type : collisionTypes) {
    ArrayRef<ValueDecl *> collidingDecls = collisions[type];
    recordShadowedDeclsAfterTypeMatch(collidingDecls, dc,
                                      shadowed);
  }
}

/// Look through the given set of declarations (that all have the same name),
/// recording those that are shadowed by another declaration in the
/// \c shadowed set.
static void recordShadowedDeclsForImportedInits(
                                ArrayRef<ConstructorDecl *> ctors,
                                llvm::SmallPtrSetImpl<ValueDecl *> &shadowed) {
  assert(ctors.size() > 1 && "No collisions");

  ASTContext &ctx = ctors.front()->getASTContext();

  // Find the "best" constructor with this signature.
  ConstructorDecl *bestCtor = ctors[0];
  for (auto ctor : ctors.slice(1)) {
    auto comparison = compareConstructors(ctor, bestCtor, ctx);
    if (comparison == ConstructorComparison::Better)
      bestCtor = ctor;
  }

  // Shadow any initializers that are worse.
  for (auto ctor : ctors) {
    auto comparison = compareConstructors(ctor, bestCtor, ctx);
    if (comparison == ConstructorComparison::Worse)
      shadowed.insert(ctor);
  }
}

/// Look through the given set of declarations (that all have the same name),
/// recording those that are shadowed by another declaration in the
/// \c shadowed set.
static void recordShadowedDecls(ArrayRef<ValueDecl *> decls,
                                const DeclContext *dc,
                                llvm::SmallPtrSetImpl<ValueDecl *> &shadowed) {
  if (decls.size() < 2)
    return;

  llvm::TinyPtrVector<ValueDecl *> typeDecls;

  // Categorize all of the declarations based on their overload signatures.
  llvm::SmallDenseMap<const GenericSignatureImpl *,
                      llvm::TinyPtrVector<ValueDecl *>> collisions;
  llvm::SmallVector<const GenericSignatureImpl *, 2> collisionSignatures;
  llvm::SmallDenseMap<NominalTypeDecl *,
                      llvm::TinyPtrVector<ConstructorDecl *>>
    importedInitializerCollisions;
  llvm::TinyPtrVector<NominalTypeDecl *> importedInitializerCollisionTypes;

  for (auto decl : decls) {
    if (auto *typeDecl = dyn_cast<TypeDecl>(decl)) {
      typeDecls.push_back(typeDecl);
      continue;
    }

    // Specifically keep track of imported initializers, which can come from
    // Objective-C init methods, Objective-C factory methods, renamed C
    // functions, or be synthesized by the importer.
    if (decl->hasClangNode() ||
        (isa<NominalTypeDecl>(decl->getDeclContext()) &&
         cast<NominalTypeDecl>(decl->getDeclContext())->hasClangNode())) {
      if (auto ctor = dyn_cast<ConstructorDecl>(decl)) {
        auto nominal = ctor->getDeclContext()->getSelfNominalTypeDecl();
        auto &knownInits = importedInitializerCollisions[nominal];
        if (knownInits.size() == 1) {
          importedInitializerCollisionTypes.push_back(nominal);
        }
        knownInits.push_back(ctor);
      }
    }

    // If the decl is currently being validated, this is likely a recursive
    // reference and we'll want to skip ahead so as to avoid having its type
    // attempt to desugar itself.
    if (decl->isRecursiveValidation())
      continue;

    // Record this declaration based on its signature.
    auto *dc = decl->getInnermostDeclContext();
    auto signature = dc->getGenericSignatureOfContext().getCanonicalSignature();
    auto &known = collisions[signature.getPointer()];
    if (known.size() == 1) {
      collisionSignatures.push_back(signature.getPointer());
    }

    known.push_back(decl);
  }

  // Check whether we have shadowing for type declarations.
  if (typeDecls.size() > 1) {
    ArrayRef<ValueDecl *> collidingDecls = typeDecls;
    recordShadowedDeclsAfterTypeMatch(collidingDecls, dc, shadowed);
  }

  // Check whether we have shadowing for signature collisions.
  for (auto signature : collisionSignatures) {
    ArrayRef<ValueDecl *> collidingDecls = collisions[signature];
    recordShadowedDeclsAfterSignatureMatch(collidingDecls, dc, shadowed);
  }

  // Check whether we have shadowing for imported initializer collisions.
  for (auto nominal : importedInitializerCollisionTypes) {
    recordShadowedDeclsForImportedInits(importedInitializerCollisions[nominal],
                                        shadowed);
  }
}

static void
recordShadowedDecls(ArrayRef<OperatorDecl *> decls, const DeclContext *dc,
                    llvm::SmallPtrSetImpl<OperatorDecl *> &shadowed) {
  // Always considered to have the same signature.
  recordShadowedDeclsAfterTypeMatch(decls, dc, shadowed);
}

static void
recordShadowedDecls(ArrayRef<PrecedenceGroupDecl *> decls,
                    const DeclContext *dc,
                    llvm::SmallPtrSetImpl<PrecedenceGroupDecl *> &shadowed) {
  // Always considered to have the same type.
  recordShadowedDeclsAfterTypeMatch(decls, dc, shadowed);
}

template <typename T, typename Container>
static bool removeShadowedDeclsImpl(Container &decls, const DeclContext *dc) {
  // Collect declarations with the same (full) name.
  llvm::SmallDenseMap<DeclName, llvm::TinyPtrVector<T>> collidingDeclGroups;
  bool anyCollisions = false;
  for (auto decl : decls) {
    // Record this declaration based on its full name.
    auto &knownDecls = collidingDeclGroups[decl->getName()];
    if (!knownDecls.empty())
      anyCollisions = true;

    knownDecls.push_back(decl);
  }

  // If nothing collided, we're done.
  if (!anyCollisions)
    return false;

  // Walk through the declarations again, marking any declarations that shadow.
  llvm::SmallPtrSet<T, 4> shadowed;
  for (auto decl : decls) {
    auto known = collidingDeclGroups.find(decl->getName());
    if (known == collidingDeclGroups.end()) {
      // We already handled this group.
      continue;
    }

    recordShadowedDecls(known->second, dc, shadowed);
    collidingDeclGroups.erase(known);
  }

  // If no declarations were shadowed, we're done.
  if (shadowed.empty())
    return false;

  // Remove shadowed declarations from the list of declarations.
  bool anyRemoved = false;
  decls.erase(std::remove_if(decls.begin(), decls.end(),
                             [&](T decl) {
                               if (shadowed.count(decl) > 0) {
                                 anyRemoved = true;
                                 return true;
                               }

                               return false;
                             }),
              decls.end());

  return anyRemoved;
}

bool swift::removeShadowedDecls(SmallVectorImpl<ValueDecl *> &decls,
                                const DeclContext *dc) {
  return removeShadowedDeclsImpl<ValueDecl *>(decls, dc);
}

bool swift::removeShadowedDecls(TinyPtrVector<OperatorDecl *> &decls,
                                const DeclContext *dc) {
#ifndef NDEBUG
  // Make sure all the operators have the same fixity.
  if (decls.size() > 1) {
    for (auto *op : decls)
      assert(op->getFixity() == decls[0]->getFixity());
  }
#endif
  return removeShadowedDeclsImpl<OperatorDecl *>(decls, dc);
}

bool swift::removeShadowedDecls(TinyPtrVector<PrecedenceGroupDecl *> &decls,
                                const DeclContext *dc) {
  return removeShadowedDeclsImpl<PrecedenceGroupDecl *>(decls, dc);
}

namespace {
enum class DiscriminatorMatch {
  NoDiscriminator,
  Matches,
  Different
};
} // end anonymous namespace

static DiscriminatorMatch matchDiscriminator(Identifier discriminator,
                                             const ValueDecl *value) {
  if (value->getFormalAccess() > AccessLevel::FilePrivate)
    return DiscriminatorMatch::NoDiscriminator;

  auto containingFile =
    dyn_cast<FileUnit>(value->getDeclContext()->getModuleScopeContext());
  if (!containingFile)
    return DiscriminatorMatch::Different;

  if (discriminator == containingFile->getDiscriminatorForPrivateDecl(value))
    return DiscriminatorMatch::Matches;

  return DiscriminatorMatch::Different;
}

static DiscriminatorMatch
matchDiscriminator(Identifier discriminator,
                   LookupResultEntry lookupResult) {
  return matchDiscriminator(discriminator, lookupResult.getValueDecl());
}

template <typename Result>
void namelookup::filterForDiscriminator(SmallVectorImpl<Result> &results,
                                        DebuggerClient *debugClient) {
  if (debugClient == nullptr)
    return;
  Identifier discriminator = debugClient->getPreferredPrivateDiscriminator();
  if (discriminator.empty())
    return;

  auto lastMatchIter = std::find_if(results.rbegin(), results.rend(),
                                    [discriminator](Result next) -> bool {
    return
      matchDiscriminator(discriminator, next) == DiscriminatorMatch::Matches;
  });
  if (lastMatchIter == results.rend())
    return;

  Result lastMatch = *lastMatchIter;

  auto newEnd = std::remove_if(results.begin(), lastMatchIter.base()-1,
                               [discriminator](Result next) -> bool {
    return
      matchDiscriminator(discriminator, next) == DiscriminatorMatch::Different;
  });
  results.erase(newEnd, results.end());
  results.push_back(lastMatch);
}

template void namelookup::filterForDiscriminator<LookupResultEntry>(
    SmallVectorImpl<LookupResultEntry> &results, DebuggerClient *debugClient);

namespace {
  /// Whether we're looking up outer results or not.
  enum class LookupOuterResults {
    Excluded,
    Included
  };
}

enum class DirectlyReferencedTypeLookupFlags {
  /// Include results that are `@inlinable` or `@usableFromInline`.
  AllowUsableFromInline = 1 << 0,

  /// Discard 'Self' requirements in protocol extension `where` clauses.
  RHSOfSelfRequirement = 1 << 1,

  /// Include results that are members of protocols to which the contextual
  /// type conforms.
  AllowProtocolMembers = 1 << 2,

  /// Include members that would normally be excluded because they come from
  /// modules that have not been imported directly.
  IgnoreMissingImports = 1 << 3,

  /// Whenther we should exclude macro expansions.
  ExcludeMacroExpansions = 1 << 4,
};

using DirectlyReferencedTypeLookupOptions =
    OptionSet<DirectlyReferencedTypeLookupFlags>;

DirectlyReferencedTypeLookupOptions defaultDirectlyReferencedTypeLookupOptions =
    DirectlyReferencedTypeLookupFlags::AllowProtocolMembers;

inline DirectlyReferencedTypeLookupOptions
operator|(DirectlyReferencedTypeLookupFlags flag1,
          DirectlyReferencedTypeLookupFlags flag2) {
  return DirectlyReferencedTypeLookupOptions(flag1) | flag2;
}

/// Retrieve the set of type declarations that are directly referenced from
/// the given parsed type representation.
static DirectlyReferencedTypeDecls
directReferencesForTypeRepr(Evaluator &evaluator, ASTContext &ctx,
                            TypeRepr *typeRepr, DeclContext *dc,
                            DirectlyReferencedTypeLookupOptions options);

/// Retrieve the set of type declarations that are directly referenced from
/// the given type.
static DirectlyReferencedTypeDecls directReferencesForType(Type type);

enum class ResolveToNominalFlags : uint8_t {
  AllowTupleType = 0x1
};

using ResolveToNominalOptions = OptionSet<ResolveToNominalFlags>;

/// Given a set of type declarations, find all of the nominal type declarations
/// that they reference, looking through typealiases as appropriate.
static TinyPtrVector<NominalTypeDecl *>
resolveTypeDeclsToNominal(Evaluator &evaluator,
                          ASTContext &ctx,
                          ArrayRef<TypeDecl *> typeDecls,
                          ResolveToNominalOptions options,
                          SmallVectorImpl<ModuleDecl *> &modulesFound,
                          bool &anyObject);

SelfBounds SelfBoundsFromWhereClauseRequest::evaluate(
    Evaluator &evaluator,
    llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl) const {
  auto *typeDecl = decl.dyn_cast<const TypeDecl *>();
  auto *protoDecl = dyn_cast_or_null<const ProtocolDecl>(typeDecl);
  auto *extDecl = decl.dyn_cast<const ExtensionDecl *>();

  const DeclContext *dc =
      protoDecl ? (const DeclContext *)protoDecl : (const DeclContext *)extDecl;

  auto requirements = protoDecl ? protoDecl->getTrailingWhereClause()
                                : extDecl->getTrailingWhereClause();

  ASTContext &ctx = dc->getASTContext();

  SelfBounds result;

  if (requirements == nullptr)
    return result;

  for (const auto &req : requirements->getRequirements()) {
    // We only care about type constraints.
    if (req.getKind() != RequirementReprKind::TypeConstraint)
      continue;

    // The left-hand side of the type constraint must be 'Self'.
    bool isSelfLHS = false;
    if (auto typeRepr = req.getSubjectRepr()) {
      isSelfLHS = typeRepr->isSimpleUnqualifiedIdentifier(ctx.Id_Self);
    }
    if (!isSelfLHS)
      continue;

    // Resolve the right-hand side.
    DirectlyReferencedTypeDecls rhsDecls;
    if (auto typeRepr = req.getConstraintRepr()) {
      auto typeLookupOptions =
          defaultDirectlyReferencedTypeLookupOptions |
          DirectlyReferencedTypeLookupFlags::RHSOfSelfRequirement;
      rhsDecls = directReferencesForTypeRepr(evaluator, ctx, typeRepr,
                                             const_cast<DeclContext *>(dc),
                                             typeLookupOptions);
    }

    SmallVector<ModuleDecl *, 2> modulesFound;
    auto rhsNominals = resolveTypeDeclsToNominal(evaluator, ctx, rhsDecls.first,
                                                 ResolveToNominalOptions(),
                                                 modulesFound,
                                                 result.anyObject);
    result.decls.insert(result.decls.end(),
                        rhsNominals.begin(),
                        rhsNominals.end());

    // Collect inverse markings on 'Self'.
    result.inverses.insertAll(rhsDecls.second);
  }

  return result;
}

SelfBounds swift::getSelfBoundsFromWhereClause(
    llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl) {
  auto *typeDecl = decl.dyn_cast<const TypeDecl *>();
  auto *extDecl = decl.dyn_cast<const ExtensionDecl *>();
  auto &ctx = typeDecl ? typeDecl->getASTContext()
                       : extDecl->getASTContext();
  return evaluateOrDefault(ctx.evaluator,
                           SelfBoundsFromWhereClauseRequest{decl}, {});
}

SelfBounds SelfBoundsFromGenericSignatureRequest::evaluate(
    Evaluator &evaluator, const ExtensionDecl *extDecl) const {
  SelfBounds result;
  auto selfType = extDecl->getSelfInterfaceType();
  for (const auto &req : extDecl->getGenericRequirements()) {
    auto kind = req.getKind();
    if (kind != RequirementKind::Conformance &&
        kind != RequirementKind::Superclass)
      continue;
    // The left-hand side of the type constraint must be 'Self'.
    if (!selfType->isEqual(req.getFirstType()))
      continue;

    result.decls.push_back(req.getSecondType()->getAnyNominal());
  }

  return result;
}

SelfBounds
swift::getSelfBoundsFromGenericSignature(const ExtensionDecl *extDecl) {
  auto &ctx = extDecl->getASTContext();
  return evaluateOrDefault(ctx.evaluator,
                           SelfBoundsFromGenericSignatureRequest{extDecl}, {});
}

DirectlyReferencedTypeDecls
TypeDeclsFromWhereClauseRequest::evaluate(Evaluator &evaluator,
                                          ExtensionDecl *ext) const {
  ASTContext &ctx = ext->getASTContext();

  DirectlyReferencedTypeDecls result;
  auto resolve = [&](TypeRepr *typeRepr) {
    auto decls =
        directReferencesForTypeRepr(evaluator, ctx, typeRepr, ext,
                                    defaultDirectlyReferencedTypeLookupOptions);
    result.first.insert(result.first.end(),
                        decls.first.begin(),
                        decls.first.end());
    result.second.insertAll(decls.second);
  };

  if (auto *whereClause = ext->getTrailingWhereClause()) {
    for (const auto &req : whereClause->getRequirements()) {
      switch (req.getKind()) {
      case RequirementReprKind::TypeConstraint:
        resolve(req.getSubjectRepr());
        resolve(req.getConstraintRepr());
        break;

      case RequirementReprKind::SameType:
        resolve(req.getFirstTypeRepr());
        resolve(req.getSecondTypeRepr());
        break;

      case RequirementReprKind::LayoutConstraint:
        resolve(req.getSubjectRepr());
        break;
      }
    }
  }

  return result;
}




#pragma mark Member lookup table

void LazyMemberLoader::anchor() {}

void LazyConformanceLoader::anchor() {}

/// Lookup table used to store members of a nominal type (and its extensions)
/// for fast retrieval.
class swift::MemberLookupTable : public ASTAllocated<swift::MemberLookupTable> {
  /// The type of the internal lookup table.
  typedef llvm::DenseMap<DeclName, llvm::TinyPtrVector<ValueDecl *>>
    LookupTable;

  /// Lookup table mapping names to the set of declarations with that name.
  LookupTable Lookup;

  /// List of containers that have lazily-loaded members
  llvm::SmallVector<ExtensionDecl *, 2> ExtensionsWithLazyMembers;

  /// The set of names of lazily-loaded members that the lookup table has a
  /// complete accounting of with respect to all known extensions of its
  /// parent nominal type.
  llvm::DenseSet<DeclBaseName> LazilyCompleteNames;

  struct {
    /// Whether we have computed the `containersWithMacroExpansions`.
    bool ComputedContainersWithMacroExpansions = false;

    /// The nominal type and any extensions that have macro expansions, which
    /// is used to restrict the set of places one will lookup for a member
    /// produced by a macro expansion.
    llvm::SmallVector<TypeOrExtensionDecl, 2> ContainersWithMacroExpansions;

    /// The set of names for which we have expanded relevant macros for in the
    /// parent nominal type.
    llvm::DenseSet<DeclName> LazilyCompleteNames;
  } LazyMacroExpansionState;
public:
  /// Create a new member lookup table.
  explicit MemberLookupTable(ASTContext &ctx);

  /// Add the given member to the lookup table.
  void addMember(Decl *members);

  /// Add the given members to the lookup table.
  void addMembers(DeclRange members);

  /// Add the members of the extension to the lookup table, if necessary
  /// registering it for future lazy member loading.
  void addExtension(ExtensionDecl *ext);

  void addExtensionWithLazyMembers(ExtensionDecl *ext) {
    ExtensionsWithLazyMembers.push_back(ext);
  }

  ArrayRef<ExtensionDecl *> getExtensionsWithLazyMembers() const {
    return ExtensionsWithLazyMembers;
  }

  /// Returns \c true if the lookup table has a complete accounting of the
  /// given name.
  bool isLazilyComplete(DeclBaseName name) const {
    return LazilyCompleteNames.contains(name);
  }

  /// Mark a given lazily-loaded name as being complete.
  void markLazilyComplete(DeclBaseName name) {
    LazilyCompleteNames.insert(name);
  }

  /// Clears the cache of lazily-complete names.  This _must_ be called when
  /// new extensions with lazy members are added to the type, or direct lookup
  /// will return inconsistent or stale results.
  void clearLazilyCompleteCache() {
    LazilyCompleteNames.clear();
  }

  /// Retrieve an array containing the set of containers for this type (
  /// i.e., the nominal type and any extensions) that can produce members via
  /// macro expansion.
  ArrayRef<TypeOrExtensionDecl> getContainersWithMacroExpansions(
      NominalTypeDecl *nominal) {
    if (LazyMacroExpansionState.ComputedContainersWithMacroExpansions)
      return LazyMacroExpansionState.ContainersWithMacroExpansions;

    LazyMacroExpansionState.ComputedContainersWithMacroExpansions = true;

    // Does the type have macro expansions?
    addContainerWithMacroExpansions(nominal);

    // Check each extension for macro expansions.
    for (auto ext : nominal->getExtensions())
      addContainerWithMacroExpansions(ext);

    return LazyMacroExpansionState.ContainersWithMacroExpansions;
  }

  void addContainerWithMacroExpansions(TypeOrExtensionDecl container){
    if (LazyMacroExpansionState.ComputedContainersWithMacroExpansions &&
        evaluateOrDefault(
                container.getAsDecl()->getASTContext().evaluator,
                PotentialMacroExpansionsInContextRequest{container}, {}))
      LazyMacroExpansionState.ContainersWithMacroExpansions.push_back(
          container);
  }

  /// Determine whether the given container has any macro-introduced names that
  /// match the given declaration.
  bool hasAnyMacroNamesMatching(TypeOrExtensionDecl container, DeclName name);

  bool isLazilyCompleteForMacroExpansion(DeclName name) const {
    assert(!MacroDecl::isUniqueMacroName(name.getBaseName()));
    // If we've already expanded macros for a simple name, we must have expanded
    // all macros that produce names with the same base identifier.
    bool isBaseNameComplete = name.isCompoundName() &&
        isLazilyCompleteForMacroExpansion(DeclName(name.getBaseName()));
    return isBaseNameComplete ||
        LazyMacroExpansionState.LazilyCompleteNames.contains(name);
  }

  void markLazilyCompleteForMacroExpansion(DeclName name) {
    assert(!MacroDecl::isUniqueMacroName(name.getBaseName()));
    LazyMacroExpansionState.LazilyCompleteNames.insert(name);
  }

  void clearLazilyCompleteForMacroExpansionCache() {
    LazyMacroExpansionState.LazilyCompleteNames.clear();
  }

  /// Iterator into the lookup table.
  typedef LookupTable::iterator iterator;

  iterator begin() { return Lookup.begin(); }
  iterator end() { return Lookup.end(); }

  iterator find(DeclName name) {
    return Lookup.find(name);
  }

  void dump(llvm::raw_ostream &os) const {
    os << "Lookup:\n  ";
    for (auto &pair : Lookup) {
      pair.getFirst().print(os);
      if (isLazilyComplete(pair.getFirst().getBaseName())) {
        os << " (lazily complete)";
      }
      os << ":\n  ";
      for (auto &decl : pair.getSecond()) {
        os << "- ";
        decl->dumpRef(os);
        os << "\n  ";
      }
    }
    os << "\n";
  }

  SWIFT_DEBUG_DUMP {
    dump(llvm::errs());
  }
};

namespace {
  /// Stores the set of Objective-C methods with a given selector within the
  /// Objective-C method lookup table.
  struct StoredObjCMethods {
    /// The generation count at which this list was last updated.
    unsigned Generation = 0;

    /// The set of methods with the given selector.
    llvm::TinyPtrVector<AbstractFunctionDecl *> Methods;
  };
} // end anonymous namespace

/// Class member lookup table, which is a member lookup table with a second
/// table for lookup based on Objective-C selector.
class swift::ObjCMethodLookupTable
        : public llvm::DenseMap<std::pair<ObjCSelector, char>,
                                StoredObjCMethods>,
          public ASTAllocated<ObjCMethodLookupTable>
{
  SWIFT_DEBUG_DUMP {
    llvm::errs() << "ObjCMethodLookupTable:\n";
    for (auto pair : *this) {
      auto selector = pair.getFirst().first;
      auto isInstanceMethod = pair.getFirst().second;
      auto &methods = pair.getSecond();

      llvm::errs() << "  \"" << (isInstanceMethod ? "-" : "+") << selector
                   << "\":\n";
      for (auto method : methods.Methods) {
        llvm::errs() << "  - \"";
        method->dumpRef(llvm::errs());
        llvm::errs() << "\"\n";
      }
    }
  }
};

MemberLookupTable::MemberLookupTable(ASTContext &ctx) {
  // Register a cleanup with the ASTContext to call the lookup table
  // destructor.
  ctx.addCleanup([this]() {
    this->~MemberLookupTable();
  });
}

void MemberLookupTable::addMember(Decl *member) {
  // Only value declarations matter.
  auto vd = dyn_cast<ValueDecl>(member);
  if (!vd)
    return;

  // @_implements members get added under their declared name.
  auto A = vd->getAttrs().getAttribute<ImplementsAttr>();

  // Unnamed entities w/o @_implements synonyms cannot be found by name lookup.
  if (!A && !vd->hasName())
    return;

  // If this declaration is already in the lookup table, don't add it
  // again.
  if (vd->isAlreadyInLookupTable()) {
    return;
  }
  vd->setAlreadyInLookupTable();

  // Add this declaration to the lookup set under its compound name and simple
  // name.
  vd->getName().addToLookupTable(Lookup, vd);

  // And if given a synonym, under that name too.
  if (A)
    A->getMemberName().addToLookupTable(Lookup, vd);

  auto abiRole = ABIRoleInfo(vd);
  if (!abiRole.providesABI() && abiRole.getCounterpart())
    addMember(abiRole.getCounterpart());
}

void MemberLookupTable::addMembers(DeclRange members) {
  for (auto member : members) {
    addMember(member);
  }
}

static bool shouldLoadMembersImmediately(ExtensionDecl *ext) {
  assert(ext->hasLazyMembers());
  if (ext->wasDeserialized() || ext->hasClangNode())
    return false;

  // This extension is lazy but is not deserialized or backed by a clang node,
  // so it's a ClangImporter extension containing import-as-member globals.
  // Historically, Swift forced these extensions to load their members
  // immediately, bypassing the module's SwiftLookupTable. Using the
  // SwiftLookupTable *ought* to work the same, but in practice it sometimes
  // gives different results when a header is not properly modularized. Provide
  // a flag to temporarily re-enable the old behavior.
  return ext->getASTContext().LangOpts.DisableNamedLazyImportAsMemberLoading;
}

void MemberLookupTable::addExtension(ExtensionDecl *ext) {
  // If we can lazy-load this extension, only take the members we've loaded
  // so far.
  if (ext->hasLazyMembers() && !shouldLoadMembersImmediately(ext)) {
    addMembers(ext->getCurrentMembersWithoutLoading());
    clearLazilyCompleteCache();
    clearLazilyCompleteForMacroExpansionCache();
    addExtensionWithLazyMembers(ext);
  } else {
    // Else, load all the members into the table.
    addMembers(ext->getMembers());
  }
  addContainerWithMacroExpansions(ext);
}

void NominalTypeDecl::addedExtension(ExtensionDecl *ext) {
  if (!LookupTable.getInt())
    return;

  auto *table = LookupTable.getPointer();
  assert(table);

  table->addExtension(ext);
}

void NominalTypeDecl::addedMember(Decl *member) {
  // If we have a lookup table, add the new member to it. If not, we'll pick up
  // this member when we first create the table.
  auto *vd = dyn_cast<ValueDecl>(member);
  if (!vd || !LookupTable.getInt())
    return;

  auto *table = LookupTable.getPointer();
  assert(table);

  table->addMember(vd);
}

void ExtensionDecl::addedMember(Decl *member) {
  // If this extension has already been bound to a nominal, add the new member
  // to the nominal's lookup table.
  if (NextExtension.getInt()) {
    auto nominal = getExtendedNominal();
    if (nominal)
      nominal->addedMember(member);
  }
}

void NominalTypeDecl::addMemberToLookupTable(Decl *member) {
  getLookupTable()->addMember(member);
}

// For lack of anywhere more sensible to put it, here's a diagram of the pieces
// involved in finding members and extensions of a NominalTypeDecl.
//
// ┌────────────────────────────┬─┐
// │IterableDeclContext         │ │     ┌─────────────────────────────┐
// │-------------------         │ │     │┌───────────────┬┐           ▼
// │Decl *LastDecl   ───────────┼─┼─────┘│Decl           ││  ┌───────────────┬┐
// │Decl *FirstDecl  ───────────┼─┼─────▶│----           ││  │Decl           ││
// │                            │ │      │Decl  *NextDecl├┼─▶│----           ││
// │bool HasLazyMembers         │ │      ├───────────────┘│  │Decl *NextDecl ││
// │IterableDeclContextKind Kind│ │      │                │  ├───────────────┘│
// │                            │ │      │ValueDecl       │  │                │
// ├────────────────────────────┘ │      │---------       │  │ValueDecl       │
// │                              │      │DeclName Name   │  │---------       │
// │NominalTypeDecl               │      └────────────────┘  │DeclName Name   │
// │---------------               │               ▲          └────────────────┘
// │ExtensionDecl *FirstExtension─┼────────┐      │                   ▲
// │ExtensionDecl *LastExtension ─┼───────┐│      │                   └───┐
// │                              │       ││      └──────────────────────┐│
// │MemberLookupTable *LookupTable├─┐     ││                             ││
// └──────────────────────────────┘ │     ││     ┌─────────────────┐     ││
//                                  │     ││     │ExtensionDecl    │     ││
//                                  │     ││     │-------------    │     ││
//                    ┌─────────────┘     │└────▶│ExtensionDecl    │     ││
//                    │                   │      │  *NextExtension ├──┐  ││
//                    ▼                   │      └─────────────────┘  │  ││
// ┌─────────────────────────────────────┐│      ┌─────────────────┐  │  ││
// │MemberLookupTable                    ││      │ExtensionDecl    │  │  ││
// │-----------------                    ││      │-------------    │  │  ││
// │ExtensionDecl *LastExtensionIncluded ├┴─────▶│ExtensionDecl    │◀─┘  ││
// │                                     │       │  *NextExtension │     ││
// │┌───────────────────────────────────┐│       └─────────────────┘     ││
// ││DenseMap<Declname, ...> LookupTable││                               ││
// ││-----------------------------------││  ┌──────────────────────────┐ ││
// ││[NameA] TinyPtrVector<ValueDecl *> ││  │TinyPtrVector<ValueDecl *>│ ││
// ││[NameB] TinyPtrVector<ValueDecl *> ││  │--------------------------│ ││
// ││[NameC] TinyPtrVector<ValueDecl *>─┼┼─▶│[0] ValueDecl *      ─────┼─┘│
// │└───────────────────────────────────┘│  │[1] ValueDecl *      ─────┼──┘
// └─────────────────────────────────────┘  └──────────────────────────┘
//
// The HasLazyMembers, Kind, and LookupTableComplete fields are packed into
// PointerIntPairs so don't go grepping for them; but for purposes of
// illustration they are effectively their own fields.
//
// MemberLookupTable is populated en-masse when the IterableDeclContext's
// (IDC's) list of Decls is populated. But MemberLookupTable can also be
// populated incrementally by one-name-at-a-time lookups by lookupDirect, in
// which case those Decls are _not_ added to the IDC's list. They are cached in
// the loader they come from, lifecycle-wise, and are added to the
// MemberLookupTable to accelerate subsequent retrieval, but the IDC is not
// considered populated until someone calls getMembers().
//
// If the IDC list is later populated and/or an extension is added _after_
// MemberLookupTable is constructed (and possibly has entries in it),
// MemberLookupTable is incrementally reconstituted with new members.

static void
populateLookupTableEntryFromLazyIDCLoader(ASTContext &ctx,
                                          MemberLookupTable &LookupTable,
                                          DeclBaseName name,
                                          IterableDeclContext *IDC) {
  if (!IDC->hasLazyMembers())
    return;

  auto ci = ctx.getOrCreateLazyIterableContextData(IDC,
                                                   /*lazyLoader=*/nullptr);
  auto res = ci->loader->loadNamedMembers(IDC, name, ci->memberData);
  if (auto s = ctx.Stats) {
    ++s->getFrontendCounters().NamedLazyMemberLoadSuccessCount;
  }
  for (auto d : res) {
    LookupTable.addMember(d);
  }
}

static void
populateLookupTableEntryFromExtensions(ASTContext &ctx,
                                       MemberLookupTable &table,
                                       DeclBaseName name,
                                       NominalTypeDecl *nominal) {
  assert(!table.isLazilyComplete(name) &&
         "Should not be searching extensions for complete name!");

  for (auto e : table.getExtensionsWithLazyMembers()) {
    // If there's no lazy members to look at, all the members of this extension
    // are present in the lookup table.
    if (!e->hasLazyMembers()) {
      continue;
    }

    assert(!e->hasUnparsedMembers());

    populateLookupTableEntryFromLazyIDCLoader(ctx, table, name, e);
  }
}

/// Adjust the given name to make it a proper key for the lazy macro expansion
/// cache, which maps all uniquely-generated names down to a single placeholder
/// key.
static DeclName adjustLazyMacroExpansionNameKey(
    ASTContext &ctx, DeclName name) {
  if (MacroDecl::isUniqueMacroName(name.getBaseName()))
    return MacroDecl::getUniqueNamePlaceholder(ctx);

  return name;
}

SmallVector<MacroDecl *, 1> namelookup::lookupMacros(DeclContext *dc,
                                                     DeclNameRef moduleName,
                                                     DeclNameRef macroName,
                                                     MacroRoles roles) {
  SmallVector<MacroDecl *, 1> choices;
  auto moduleScopeDC = getModuleScopeLookupContext(dc);
  ASTContext &ctx = moduleScopeDC->getASTContext();

  auto addChoiceIfApplicable = [&](ValueDecl *decl) {
    if (auto macro = dyn_cast<MacroDecl>(decl)) {
      auto candidateRoles = macro->getMacroRoles();
      if ((candidateRoles && roles.contains(candidateRoles)) ||
          // FIXME: `externalMacro` should have all roles.
          macro->getBaseIdentifier().str() == "externalMacro") {
        choices.push_back(macro);
      }
    }
  };

  // When a module is specified, it's a module-qualified lookup.
  if (moduleName) {
    UnqualifiedLookupDescriptor moduleLookupDesc(
        moduleName, moduleScopeDC, SourceLoc(),
        UnqualifiedLookupFlags::ModuleLookup);
    auto moduleLookup = evaluateOrDefault(
        ctx.evaluator, UnqualifiedLookupRequest{moduleLookupDesc}, {});
    auto foundTypeDecl = moduleLookup.getSingleTypeResult();
    auto *moduleDecl = dyn_cast_or_null<ModuleDecl>(foundTypeDecl);

    // When resolving macro names for imported entities, we look for any
    // loaded module.
    if (!moduleDecl && isa<ClangModuleUnit>(moduleScopeDC) &&
        ctx.LangOpts.hasFeature(Feature::MacrosOnImports)) {
      moduleDecl = ctx.getLoadedModule(moduleName.getBaseIdentifier());
      moduleScopeDC = moduleDecl;
    }

    if (!moduleDecl)
      return {};

    ModuleQualifiedLookupRequest req{moduleScopeDC, moduleDecl, macroName,
                                     SourceLoc(),
                                     NL_ExcludeMacroExpansions | NL_OnlyMacros};
    auto lookup = evaluateOrDefault(ctx.evaluator, req, {});
    for (auto *found : lookup)
      addChoiceIfApplicable(found);
  }
  // Otherwise it's an unqualified lookup.
  else {
    // Macro lookup should always exclude macro expansions; macro
    // expansions cannot introduce new macro declarations. Note that
    // the source location here doesn't matter.
    UnqualifiedLookupDescriptor descriptor{
        macroName, moduleScopeDC, SourceLoc(),
        UnqualifiedLookupFlags::ExcludeMacroExpansions |
            UnqualifiedLookupFlags::MacroLookup};

    auto lookup = evaluateOrDefault(ctx.evaluator,
                                    UnqualifiedLookupRequest{descriptor}, {});

    for (const auto &found : lookup.allResults())
      addChoiceIfApplicable(found.getValueDecl());
  }

  return choices;
}

bool
namelookup::isInMacroArgument(SourceFile *sourceFile, SourceLoc loc) {
  bool inMacroArgument = false;

  // Make sure that the source location is actually within the given source
  // file.
  if (sourceFile && loc.isValid()) {
    sourceFile =
        sourceFile->getParentModule()->getSourceFileContainingLocation(loc);
    if (!sourceFile)
      return false;
  }

  ASTScope::lookupEnclosingMacroScope(
      sourceFile, loc,
      [&](auto potentialMacro) -> bool {
        UnresolvedMacroReference macro(potentialMacro);

        if (macro.getFreestanding()) {
          inMacroArgument = true;
        } else if (macro.getAttr()) {
          auto *moduleScope = sourceFile->getModuleScopeContext();
          auto results =
              lookupMacros(moduleScope, macro.getModuleName(),
                           macro.getMacroName(), getAttachedMacroRoles());
          inMacroArgument = !results.empty();
        }

        return inMacroArgument;
      });

  return inMacroArgument;
}

/// Call the given function body with each macro declaration and its associated
/// role attribute for the given role.
///
/// This routine intentionally avoids calling `forEachAttachedMacro`, which
/// triggers request cycles.
void namelookup::forEachPotentialResolvedMacro(
    DeclContext *moduleScopeCtx, DeclNameRef macroName, MacroRole role,
    llvm::function_ref<void(MacroDecl *, const MacroRoleAttr *)> body
) {
  ASTContext &ctx = moduleScopeCtx->getASTContext();
  UnqualifiedLookupDescriptor lookupDesc{
      macroName, moduleScopeCtx, SourceLoc(),
      UnqualifiedLookupFlags::ExcludeMacroExpansions |
          UnqualifiedLookupFlags::MacroLookup};

  auto lookup = evaluateOrDefault(
      ctx.evaluator, UnqualifiedLookupRequest{lookupDesc}, {});
  for (auto result : lookup.allResults()) {
    auto *vd = result.getValueDecl();
    auto *macro = dyn_cast<MacroDecl>(vd);
    if (!macro)
      continue;

    auto *macroRoleAttr = macro->getMacroRoleAttr(role);
    if (!macroRoleAttr)
      continue;

    body(macro, macroRoleAttr);
  }
}

/// For each macro with the given role that might be attached to the given
/// declaration, call the body.
void namelookup::forEachPotentialAttachedMacro(
    Decl *decl, MacroRole role,
    llvm::function_ref<void(MacroDecl *macro, const MacroRoleAttr *)> body
) {
  // We intentionally avoid calling `forEachAttachedMacro` in order to avoid
  // a request cycle.
  auto moduleScopeCtx = decl->getDeclContext()->getModuleScopeContext();
  for (auto attrConst : decl->getExpandedAttrs().getAttributes<CustomAttr>()) {
    auto *attr = const_cast<CustomAttr *>(attrConst);
    UnresolvedMacroReference macroRef(attr);
    auto macroName = macroRef.getMacroName();
    forEachPotentialResolvedMacro(moduleScopeCtx, macroName, role, body);
  }
}

namespace {
  /// Function object that tracks macro-introduced names.
  struct MacroIntroducedNameTracker {
    ValueDecl *attachedTo = nullptr;

    PotentialMacroExpansions potentialExpansions;

    /// Augment the set of names with those introduced by the given macro.
    void operator()(MacroDecl *macro, const MacroRoleAttr *attr) {
      potentialExpansions.noteExpandedMacro();

      // First check for arbitrary names.
      if (attr->hasNameKind(MacroIntroducedDeclNameKind::Arbitrary)) {
        potentialExpansions.noteIntroducesArbitraryNames();
      }

      // If this introduces arbitrary names, there's nothing more to do.
      if (potentialExpansions.introducesArbitraryNames())
        return;

      SmallVector<DeclName, 4> introducedNames;
      macro->getIntroducedNames(
          attr->getMacroRole(), attachedTo, introducedNames);
      for (auto name : introducedNames)
        potentialExpansions.addIntroducedMacroName(name);
    }

    bool shouldExpandForName(DeclName name) const {
      return potentialExpansions.shouldExpandForName(name);
    }
  };
}

/// Given an extension declaration, return the extended nominal type if the
/// extension was produced by expanding an extension or conformance macro from
/// the nominal declaration itself.
static NominalTypeDecl *nominalForExpandedExtensionDecl(ExtensionDecl *ext) {
  if (!ext->isInMacroExpansionInContext())
    return nullptr;


  return ext->getSelfNominalTypeDecl();
}

PotentialMacroExpansions PotentialMacroExpansionsInContextRequest::evaluate(
    Evaluator &evaluator, TypeOrExtensionDecl container) const {
  /// The implementation here needs to be kept in sync with
  /// populateLookupTableEntryFromMacroExpansions.
  MacroIntroducedNameTracker nameTracker;

  // Member macros on the type or extension.
  auto containerDecl = container.getAsDecl();
  forEachPotentialAttachedMacro(containerDecl, MacroRole::Member, nameTracker);

  // Extension macros on the type or extension.
  {
    NominalTypeDecl *nominal = nullptr;
    // If the container is an extension that was created from an extension
    // macro, look at the nominal declaration to find any extension macros.
    if (auto ext = dyn_cast<ExtensionDecl>(containerDecl))
      nominal = nominalForExpandedExtensionDecl(ext);
    else
      nominal = container.getBaseNominal();

    if (nominal)
      forEachPotentialAttachedMacro(nominal, MacroRole::Extension, nameTracker);
  }

  // Peer and freestanding declaration macros.
  auto dc = container.getAsDeclContext();
  auto idc = container.getAsIterableDeclContext();
  for (auto *member : idc->getCurrentMembersWithoutLoading()) {
    if (auto *med = dyn_cast<MacroExpansionDecl>(member)) {
      nameTracker.attachedTo = nullptr;
      forEachPotentialResolvedMacro(
          dc->getModuleScopeContext(), med->getMacroName(),
          MacroRole::Declaration, nameTracker);
    } else if (auto *vd = dyn_cast<ValueDecl>(member)) {
      nameTracker.attachedTo = vd;
      forEachPotentialAttachedMacro(member, MacroRole::Peer, nameTracker);
    }
  }

  nameTracker.attachedTo = nullptr;
  return nameTracker.potentialExpansions;
}

bool MemberLookupTable::hasAnyMacroNamesMatching(
    TypeOrExtensionDecl container, DeclName name) {
  ASTContext &ctx = container.getAsDecl()->getASTContext();
  auto potentialExpansions = evaluateOrDefault(
      ctx.evaluator, PotentialMacroExpansionsInContextRequest{container},
      PotentialMacroExpansions());

  return potentialExpansions.shouldExpandForName(name);
}

static void
populateLookupTableEntryFromMacroExpansions(ASTContext &ctx,
                                            MemberLookupTable &table,
                                            DeclName name,
                                            TypeOrExtensionDecl container) {
  // If there are no macro-introduced names in this container that match the
  // given name, do nothing. This avoids an expensive walk over the members
  // and attributes for the common case where there are no macros.
  if (!table.hasAnyMacroNamesMatching(container, name))
    return;

  // Trigger the expansion of member macros on the container, if any of the
  // names match.
  {
    MacroIntroducedNameTracker nameTracker;
    auto decl = container.getAsDecl();
    forEachPotentialAttachedMacro(decl, MacroRole::Member, nameTracker);
    if (nameTracker.shouldExpandForName(name)) {
      (void)evaluateOrDefault(
          ctx.evaluator,
          ExpandSynthesizedMemberMacroRequest{decl},
          false);
    }
  }

  // Trigger the expansion of extension macros on the container, if any of the
  // names match.
  {
    MacroIntroducedNameTracker nameTracker;
    NominalTypeDecl *nominal = nullptr;
    // If the container is an extension that was created from an extension
    // macro, look at the nominal declaration to find any extension macros.
    if (auto ext = dyn_cast<ExtensionDecl>(container.getAsDecl()))
      nominal = nominalForExpandedExtensionDecl(ext);
    else
      nominal = container.getBaseNominal();

    if (nominal) {
      forEachPotentialAttachedMacro(nominal,
                                  MacroRole::Extension, nameTracker);
      if (nameTracker.shouldExpandForName(name)) {
        (void)evaluateOrDefault(ctx.evaluator, ExpandExtensionMacros{nominal},
                                false);
      }
    }
  }

  auto dc = container.getAsDeclContext();
  auto *module = dc->getParentModule();
  auto idc = container.getAsIterableDeclContext();
  for (auto *member : idc->getCurrentMembersWithoutLoading()) {
    // Collect all macro introduced names, along with its corresponding macro
    // reference. We need the macro reference to prevent adding auxiliary decls
    // that weren't introduced by the macro.

    std::deque<Decl *> mightIntroduceNames;
    mightIntroduceNames.push_back(member);

    while (!mightIntroduceNames.empty()) {
      auto *member = mightIntroduceNames.front();

      MacroIntroducedNameTracker nameTracker;
      if (auto *med = dyn_cast<MacroExpansionDecl>(member)) {
        forEachPotentialResolvedMacro(
            dc->getModuleScopeContext(), med->getMacroName(),
            MacroRole::Declaration, nameTracker);
      } else if (auto *vd = dyn_cast<ValueDecl>(member)) {
        nameTracker.attachedTo = vd;
        forEachPotentialAttachedMacro(member, MacroRole::Peer, nameTracker);
      }

      // Expand macros on this member.
      if (nameTracker.shouldExpandForName(name)) {
        member->visitAuxiliaryDecls([&](Decl *decl) {
          auto *sf = module->getSourceFileContainingLocation(decl->getLoc());
          // Bail out if the auxiliary decl was not produced by a macro.
          if (!sf || sf->Kind != SourceFileKind::MacroExpansion)
            return;

          mightIntroduceNames.push_back(decl);
          table.addMember(decl);
        });
      }

      mightIntroduceNames.pop_front();
    }
  }
}

MemberLookupTable *NominalTypeDecl::getLookupTable() {
  if (!LookupTable.getPointer()) {
    auto &ctx = getASTContext();
    LookupTable.setPointer(new (ctx) MemberLookupTable(ctx));
  }

  return LookupTable.getPointer();
}

void NominalTypeDecl::prepareLookupTable() {
  // If we have already prepared the lookup table, then there's nothing further
  // to do.
  if (LookupTable.getInt())
    return;

  auto *table = getLookupTable();

  // Otherwise start the first fill.
  if (hasLazyMembers()) {
    assert(!hasUnparsedMembers());
    table->addMembers(getCurrentMembersWithoutLoading());
  } else {
    table->addMembers(getMembers());
  }

  // Note: this calls prepareExtensions()
  for (auto e : getExtensions()) {
    table->addExtension(e);
  }

  // Any extensions added after this point will add their members to the
  // lookup table.
  LookupTable.setInt(true);
}

static TinyPtrVector<ValueDecl *> maybeFilterOutUnwantedDecls(
      TinyPtrVector<ValueDecl *> decls,
      DeclName name,
      OptionSet<NominalTypeDecl::LookupDirectFlags> flags) {
  using Flags = NominalTypeDecl::LookupDirectFlags;

  TinyPtrVector<ValueDecl*> result;
  for (auto V : decls) {
    // If we're supposed to exclude anything that comes from a macro expansion,
    // check whether the source location of the declaration is in a macro
    // expansion, and skip this declaration if it does.
    if (flags.contains(Flags::ExcludeMacroExpansions)) {
      auto sourceFile =
          V->getModuleContext()->getSourceFileContainingLocation(V->getLoc());
      if (sourceFile && sourceFile->Kind == SourceFileKind::MacroExpansion)
        continue;
    }

    // If this decl is on either side of an @abi attribute, make sure it's on
    // the side we want.
    if (!ABIRoleInfo(V).matchesOptions(flags))
      continue;

    // Filter-out any decl that doesn't have the name we're looking for
    // (asserting as a consistency-check that such entries all have
    // @_implements attrs for the name!)
    if (flags.contains(Flags::IncludeAttrImplements)
            || V->getName().matchesRef(name)) {
      result.push_back(V);
    } else {
      auto A = V->getAttrs().getAttribute<ImplementsAttr>();
      (void)A;
      assert(A && A->getMemberName().matchesRef(name));
    }
  }
  return result;
}

TinyPtrVector<ValueDecl *>
NominalTypeDecl::lookupDirect(DeclName name, SourceLoc loc,
                              OptionSet<LookupDirectFlags> flags) {
  return evaluateOrDefault(getASTContext().evaluator,
                           DirectLookupRequest({this, name, flags}, loc), {});
}

TinyPtrVector<ValueDecl *>
DirectLookupRequest::evaluate(Evaluator &evaluator,
                              DirectLookupDescriptor desc) const {
  const auto &name = desc.Name;
  const auto flags = desc.Options;
  auto *decl = desc.DC;

  ASTContext &ctx = decl->getASTContext();
  const bool excludeMacroExpansions =
      flags.contains(NominalTypeDecl::LookupDirectFlags::ExcludeMacroExpansions);

  LLVM_DEBUG(llvm::dbgs() << decl->getNameStr() << ".lookupDirect("
                          << name << ")"
                          << ", excludeMacroExpansions="
                          << excludeMacroExpansions
                          << "\n");

  decl->prepareLookupTable();

  // Call prepareExtensions() to ensure we properly invalidate the
  // lazily-complete cache for any extensions brought in by modules
  // loaded after-the-fact. This can happen with the LLDB REPL.
  decl->prepareExtensions();

  auto &Table = *decl->getLookupTable();
  if (!Table.isLazilyComplete(name.getBaseName())) {
    DeclBaseName baseName(name.getBaseName());

    if (isa_and_nonnull<clang::NamespaceDecl>(decl->getClangDecl())) {
      auto allFound = evaluateOrDefault(
          ctx.evaluator, CXXNamespaceMemberLookup({cast<EnumDecl>(decl), name}),
          {});
      populateLookupTableEntryFromExtensions(ctx, Table, baseName, decl);

      // Bypass the regular member lookup table if we find something in
      // the original C++ namespace. We don't want to store the C++ decl in the
      // lookup table as the decl can be referenced  from multiple namespace
      // declarations due to inline namespaces. We still merge in the other
      // entries found in the lookup table, to support finding members in
      // namespace extensions.
      if (!allFound.empty()) {
        auto known = Table.find(name);
        if (known != Table.end()) {
          auto swiftLookupResult =
              maybeFilterOutUnwantedDecls(known->second, name, flags);
          for (auto foundSwiftDecl : swiftLookupResult) {
            allFound.push_back(foundSwiftDecl);
          }
        }
        return allFound;
      }
    } else if (isa_and_nonnull<clang::RecordDecl>(decl->getClangDecl())) {
      auto allFound = evaluateOrDefault(
          ctx.evaluator,
          ClangRecordMemberLookup({cast<NominalTypeDecl>(decl), name}), {});
      // Add all the members we found, later we'll combine these with the
      // existing members.
      for (auto found : allFound)
        Table.addMember(found);

      populateLookupTableEntryFromExtensions(ctx, Table, baseName, decl);
    } else {
      // The lookup table believes it doesn't have a complete accounting of this
      // name - either because we're never seen it before, or another extension
      // was registered since the last time we searched. Ask the loaders to give
      // us a hand.
      populateLookupTableEntryFromLazyIDCLoader(ctx, Table, baseName, decl);
      populateLookupTableEntryFromExtensions(ctx, Table, baseName, decl);
    }

    Table.markLazilyComplete(baseName);
  }

  DeclName macroExpansionKey = adjustLazyMacroExpansionNameKey(ctx, name);
  if (!excludeMacroExpansions &&
      !Table.isLazilyCompleteForMacroExpansion(macroExpansionKey)) {
    for (auto container : Table.getContainersWithMacroExpansions(decl)) {
      populateLookupTableEntryFromMacroExpansions(
          ctx, Table, macroExpansionKey, container);
    }
    Table.markLazilyCompleteForMacroExpansion(macroExpansionKey);
  }

  // Look for a declaration with this name.
  auto known = Table.find(name);
  if (known == Table.end()) {
    return TinyPtrVector<ValueDecl *>();
  }

  // We found something; return it.
  return maybeFilterOutUnwantedDecls(known->second, name, flags);
}

bool NominalTypeDecl::createObjCMethodLookup() {
  assert(!ObjCMethodLookup && "Already have an Objective-C member table");

  // Most types cannot have ObjC methods.
  if (!(isa<ClassDecl>(this) || isa<ProtocolDecl>(this)))
    return false;

  auto &ctx = getASTContext();
  ObjCMethodLookup = new (ctx) ObjCMethodLookupTable();

  // Register a cleanup with the ASTContext to call the lookup table
  // destructor.
  ctx.addDestructorCleanup(*ObjCMethodLookup);

  return true;
}

TinyPtrVector<AbstractFunctionDecl *>
NominalTypeDecl::lookupDirect(ObjCSelector selector, bool isInstance) {
  if (!ObjCMethodLookup && !createObjCMethodLookup())
    return {};

  // If any modules have been loaded since we did the search last (or if we
  // hadn't searched before), look in those modules, too.
  auto &stored = (*ObjCMethodLookup)[{selector, isInstance}];
  ASTContext &ctx = getASTContext();
  if (ctx.getCurrentGeneration() > stored.Generation) {
    ctx.loadObjCMethods(this, selector, isInstance, stored.Generation,
                        stored.Methods);
    stored.Generation = ctx.getCurrentGeneration();
  }

  return stored.Methods;
}

static bool inObjCImplExtension(AbstractFunctionDecl *newDecl) {
  if (auto ext = dyn_cast<ExtensionDecl>(newDecl->getDeclContext()))
    return ext->isObjCImplementation();
  return false;
}

/// If there is an apparent conflict between \p newDecl and one of the methods
/// in \p vec, should we diagnose it?
static bool
shouldDiagnoseConflict(NominalTypeDecl *ty, AbstractFunctionDecl *newDecl,
                       llvm::TinyPtrVector<AbstractFunctionDecl *> &vec) {
  // Conflicts between member implementations and their interfaces, or
  // inherited inits and their overrides in @_objcImpl extensions, are spurious.
  if (newDecl->isObjCMemberImplementation()
      || (isa<ConstructorDecl>(newDecl) && inObjCImplExtension(newDecl)
          && newDecl->getAttrs().hasAttribute<OverrideAttr>()))
    return false;

  // Are all conflicting methods imported from ObjC and in our ObjC half or a
  // bridging header? Some code bases implement ObjC methods in Swift even
  // though it's not exactly supported.
  auto newDeclModuleName = newDecl->getModuleContext()->getName();
  auto newDeclPrivateModuleName = newDecl->getASTContext().getIdentifier(
                     (llvm::Twine(newDeclModuleName.str()) + "_Private").str());
  auto bridgingHeaderModuleName = newDecl->getASTContext().getIdentifier(
                                                     CLANG_HEADER_MODULE_NAME);
  if (llvm::all_of(vec, [&](AbstractFunctionDecl *oldDecl) {
    if (!oldDecl->hasClangNode())
      return false;
    auto oldDeclModuleName = oldDecl->getModuleContext()->getName();
    return oldDeclModuleName == newDeclModuleName
               || oldDeclModuleName == newDeclPrivateModuleName
               || oldDeclModuleName == bridgingHeaderModuleName;
  }))
    return false;

  return true;
}

void NominalTypeDecl::recordObjCMethod(AbstractFunctionDecl *method,
                                       ObjCSelector selector) {
  if (!ObjCMethodLookup && !createObjCMethodLookup())
    return;

  // Only record API decls.
  Decl *abiRoleDecl = method;
  if (auto accessor = dyn_cast<AccessorDecl>(method))
    abiRoleDecl = accessor->getStorage();
  if (!ABIRoleInfo(abiRoleDecl).providesAPI())
    return;

  // Record the method.
  bool isInstanceMethod = method->isObjCInstanceMethod();
  auto &vec = (*ObjCMethodLookup)[{selector, isInstanceMethod}].Methods;

  // Check whether we have a duplicate. This only checks more than one
  // element in ill-formed code, so the linear search is acceptable.
  if (std::find(vec.begin(), vec.end(), method) != vec.end())
    return;

  if (auto *sf = method->getParentSourceFile()) {
    if (vec.empty()) {
      sf->ObjCMethodList.push_back(method);
    } else if (shouldDiagnoseConflict(this, method, vec)) {
      // We have a conflict.
      sf->ObjCMethodConflicts.insert({ this, selector, isInstanceMethod });
    }
  }

  vec.push_back(method);
}

ObjCCategoryNameMap
ObjCCategoryNameMapRequest::evaluate(Evaluator &evaluator,
                                     ClassDecl *classDecl,
                                     ExtensionDecl *lastExtension) const {
  // The purpose of the `lastExtension` parameter is to bake something into the
  // request that will change when another extension is added. This ensures that
  // if more extensions are added later, we don't return an outdated version of
  // the extension map by accident.

  ObjCCategoryNameMap results;

  for (auto ext : classDecl->getExtensions()) {
    auto catName = ext->getObjCCategoryName();
    if (!catName.empty())
      results[catName].push_back(ext);

    if (ext == lastExtension)
      break;
  }

  return results;
}

ObjCCategoryNameMap ClassDecl::getObjCCategoryNameMap() {
  return evaluateOrDefault(getASTContext().evaluator,
                           ObjCCategoryNameMapRequest{this},
                           ObjCCategoryNameMap());
}

/// Determines whether MemberImportVisiblity should be enforced for lookups in
/// the given context.
static bool shouldRequireImportsInContext(const DeclContext *lookupContext) {
  auto &ctx = lookupContext->getASTContext();

  if (!ctx.LangOpts.hasFeature(Feature::MemberImportVisibility,
                               /*allowMigration=*/true))
    return false;

  // Code outside of the main module (which is often synthesized) isn't subject
  // to MemberImportVisibility rules.
  if (lookupContext->getParentModule() != ctx.MainModule)
    return false;

  return true;
}

/// Determine whether the given declaration is an acceptable lookup
/// result when searching from the given DeclContext.
static bool isAcceptableLookupResult(const DeclContext *dc, NLOptions options,
                                     ValueDecl *decl,
                                     bool onlyCompleteObjectInits,
                                     bool requireImport) {
  auto &ctx = dc->getASTContext();

  // Filter out designated initializers, if requested.
  if (onlyCompleteObjectInits) {
    if (auto ctor = dyn_cast<ConstructorDecl>(decl)) {
      if (isa<ClassDecl>(ctor->getDeclContext()) && !ctor->isInheritable())
        return false;
    } else {
      return false;
    }
  }

  // Ignore stub implementations.
  if (auto ctor = dyn_cast<ConstructorDecl>(decl)) {
    if (ctor->hasStubImplementation())
      return false;
  }

  // Check access.
  if (!(options & NL_IgnoreAccessControl) && !ctx.isAccessControlDisabled()) {
    bool allowUsableFromInline = options & NL_IncludeUsableFromInline;
    if (!decl->isAccessibleFrom(dc, /*forConformance*/ false,
                                allowUsableFromInline))
      return false;
  }

  if (requireImport) {
    // Check that there is some import in the originating context that makes
    // this decl visible.
    if (!(options & NL_IgnoreMissingImports)) {
      if (!dc->isDeclImported(decl))
        return false;
    }

    // Unlike in Swift, Obj-C allows method overrides to be declared in
    // extensions (categories), even outside of the module that defines the
    // type that is being extended. When MemberImportVisibility is enabled,
    // if these overrides are not filtered out they can hijack name
    // lookup and cause the compiler to insist that the module that defines
    // the extension be imported, contrary to developer expectations.
    //
    // Filter results belonging to these extensions out, even when ignoring
    // missing imports, if we're in a context that requires imports to access
    // member declarations.
    if (decl->getOverriddenDecl()) {
      if (auto *extension = dyn_cast<ExtensionDecl>(decl->getDeclContext())) {
        if (auto *nominal = extension->getExtendedNominal()) {
          auto extensionMod = extension->getModuleContext();
          auto nominalMod = nominal->getModuleContext();
          if (!extensionMod->isSameModuleLookingThroughOverlays(nominalMod) &&
              !dc->isDeclImported(extension))
            return false;
        }
      }
    }
  }

  // Check that it has the appropriate ABI role.
  if (!ABIRoleInfo(decl).matchesOptions(options))
    return false;

  return true;
}

bool namelookup::isInABIAttr(SourceFile *sourceFile, SourceLoc loc) {
  // Make sure that the source location is actually within the given source
  // file.
  if (sourceFile && loc.isValid()) {
    sourceFile =
        sourceFile->getParentModule()->getSourceFileContainingLocation(loc);
    if (!sourceFile)
      return false;
  }

  return ASTScope::lookupEnclosingABIAttributeScope(sourceFile, loc) != nullptr;
}

void namelookup::pruneLookupResultSet(const DeclContext *dc, NLOptions options,
                                      Identifier moduleSelector,
                                      SmallVectorImpl<ValueDecl *> &decls) {
  // If we're supposed to remove overridden declarations, do so now.
  if (options & NL_RemoveOverridden)
    removeOverriddenDecls(decls);

  // If we're supposed to remove shadowed/hidden declarations, do so now.
  if (options & NL_RemoveNonVisible) {
    removeOutOfModuleDecls(decls, moduleSelector, dc);
    removeShadowedDecls(decls, dc);
  }

  ModuleDecl *M = dc->getParentModule();
  filterForDiscriminator(decls, M->getDebugClient());
}

// An unfortunate hack to kick the decl checker into adding semantic members to
// the current type before we attempt a semantic lookup. The places this method
// looks needs to be in sync with \c extractDirectlyReferencedNominalTypes.
// See the note in \c synthesizeSemanticMembersIfNeeded about a better, more
// just, and peaceful world.
void namelookup::installSemanticMembersIfNeeded(Type type, DeclNameRef name) {
  // Look-through class-bound archetypes to ensure we synthesize e.g.
  // inherited constructors.
  if (auto archetypeTy = type->getAs<ArchetypeType>()) {
    if (auto super = archetypeTy->getSuperclass()) {
      type = super;
    }
  }

  if (type->isExistentialType()) {
    auto layout = type->getExistentialLayout();
    if (auto super = layout.explicitSuperclass) {
      type = super;
    }
  }

  if (auto *current = type->getAnyNominal()) {
    current->synthesizeSemanticMembersIfNeeded(name.getFullName());
  }
}

/// Inspect the given type to determine which nominal type declarations it
/// directly references, to facilitate name lookup into those types.
void namelookup::extractDirectlyReferencedNominalTypes(
    Type type, SmallVectorImpl<NominalTypeDecl *> &decls) {
  if (auto nominal = type->getAnyNominal()) {
    decls.push_back(nominal);
    return;
  }

  if (auto unbound = type->getAs<UnboundGenericType>()) {
    if (auto nominal = dyn_cast<NominalTypeDecl>(unbound->getDecl()))
      decls.push_back(nominal);
    return;
  }

  if (auto archetypeTy = type->getAs<ArchetypeType>()) {
    // Look in the protocols to which the archetype conforms (always).
    for (auto proto : archetypeTy->getConformsTo())
      decls.push_back(proto);

    // Look into the superclasses of this archetype.
    if (auto superclass = archetypeTy->getSuperclass()) {
      if (auto superclassDecl = superclass->getClassOrBoundGenericClass())
        decls.push_back(superclassDecl);
    }

    return;
  }

  if (auto compositionTy = type->getAs<ProtocolCompositionType>()) {
    auto layout = compositionTy->getExistentialLayout();

    for (auto protoDecl : layout.getProtocols()) {
      decls.push_back(protoDecl);
    }

    if (auto superclass = layout.explicitSuperclass) {
      auto *superclassDecl = superclass->getClassOrBoundGenericClass();
      if (superclassDecl)
        decls.push_back(superclassDecl);
    }

    return;
  }

  if (auto existential = type->getAs<ExistentialType>()) {
    extractDirectlyReferencedNominalTypes(
        existential->getConstraintType(), decls);
    return;
  }

  if (type->is<TupleType>()) {
    decls.push_back(type->getASTContext().getBuiltinTupleDecl());
    return;
  }

  llvm_unreachable("Not a type containing nominal types?");
}

void namelookup::tryExtractDirectlyReferencedNominalTypes(
    Type type, SmallVectorImpl<NominalTypeDecl *> &decls) {
  if (!type->is<ModuleType>() && type->mayHaveMembers())
    namelookup::extractDirectlyReferencedNominalTypes(type, decls);
}

bool DeclContext::lookupQualified(Type type,
                                  DeclNameRef member,
                                  SourceLoc loc,
                                  NLOptions options,
                                  SmallVectorImpl<ValueDecl *> &decls) const {
  using namespace namelookup;
  assert(decls.empty() && "additive lookup not supported");

  // Handle AnyObject lookup.
  if (type->isAnyObject()) {
    AnyObjectLookupRequest req(this, member, options);
    decls = evaluateOrDefault(getASTContext().evaluator, req, {});
    return !decls.empty();
  }

  // Handle lookup in a module.
  if (auto moduleTy = type->getAs<ModuleType>())
    return lookupQualified(moduleTy->getModule(), member,
                           loc, options, decls);

  // Figure out which nominal types we will look into.
  SmallVector<NominalTypeDecl *, 4> nominalTypesToLookInto;
  namelookup::extractDirectlyReferencedNominalTypes(type,
                                                    nominalTypesToLookInto);

  return lookupQualified(nominalTypesToLookInto, member,
                         loc, options, decls);
}

bool DeclContext::isDeclImported(const Decl *decl) const {
  auto declModule = decl->getModuleContextForNameLookup();
  return getASTContext().getImportCache().isImportedBy(declModule, this);
}

static void installPropertyWrapperMembersIfNeeded(NominalTypeDecl *target,
                                                  DeclNameRef member) {
  auto &Context = target->getASTContext();
  auto baseName = member.getBaseName();
  if (!member.isSimpleName() || baseName.isSpecial())
    return;

  if ((!baseName.getIdentifier().str().starts_with("$") &&
       !baseName.getIdentifier().hasUnderscoredNaming()) ||
      baseName.getIdentifier().str().size() <= 1) {
    return;
  }

  // $- and _-prefixed variables can be generated by properties that have
  // attached property wrappers.
  auto originalPropertyName =
      Context.getIdentifier(baseName.getIdentifier().str().substr(1));
  for (auto member : target->lookupDirect(originalPropertyName)) {
    if (auto var = dyn_cast<VarDecl>(member)) {
      if (var->hasAttachedPropertyWrapper()) {
        auto sourceFile = var->getDeclContext()->getParentSourceFile();
        if (sourceFile && sourceFile->Kind != SourceFileKind::Interface) {
          (void)var->getPropertyWrapperAuxiliaryVariables();
          (void)var->getPropertyWrapperInitializerInfo();
        }
      }
    }
  }
}

bool DeclContext::lookupQualified(ArrayRef<NominalTypeDecl *> typeDecls,
                                  DeclNameRef member,
                                  SourceLoc loc, NLOptions options,
                                  SmallVectorImpl<ValueDecl *> &decls) const {
  assert(decls.empty() && "additive lookup not supported");
  QualifiedLookupRequest req{this, {typeDecls.begin(), typeDecls.end()},
                             member, loc, options};
  decls = evaluateOrDefault(getASTContext().evaluator, req, {});
  return !decls.empty();
}

QualifiedLookupResult
QualifiedLookupRequest::evaluate(Evaluator &eval, const DeclContext *DC,
                                 SmallVector<NominalTypeDecl *, 4> typeDecls,
                                 DeclNameRef member, NLOptions options) const {
  using namespace namelookup;
  QualifiedLookupResult decls;

  // Tracking for the nominal types we'll visit.
  SmallVector<NominalTypeDecl *, 4> stack;
  llvm::SmallPtrSet<NominalTypeDecl *, 4> visited;
  bool sawClassDecl = false;

  // Add the given nominal type to the stack.
  auto addNominalType = [&](NominalTypeDecl *nominal) {
    if (!visited.insert(nominal).second)
      return false;

    if (isa<ClassDecl>(nominal))
      sawClassDecl = true;

    stack.push_back(nominal);
    return true;
  };

  // Add all of the nominal types to the stack.
  for (auto nominal : typeDecls) {
    addNominalType(nominal);
  }

  // Whether we only want to return complete object initializers.
  bool onlyCompleteObjectInits = false;

  // Whether to enforce MemberImportVisibility import restrictions.
  bool requireImport = shouldRequireImportsInContext(DC);

  // Visit all of the nominal types we know about, discovering any others
  // we need along the way.
  bool wantProtocolMembers = (options & NL_ProtocolMembers);
  while (!stack.empty()) {
    auto current = stack.back();
    stack.pop_back();

    // Make sure we've resolved property wrappers, if we need them.
    installPropertyWrapperMembersIfNeeded(current, member);

    // Look for results within the current nominal type and its extensions.
    bool currentIsProtocol = isa<ProtocolDecl>(current);
    auto flags = OptionSet<NominalTypeDecl::LookupDirectFlags>();
    if (options & NL_IncludeAttributeImplements)
      flags |= NominalTypeDecl::LookupDirectFlags::IncludeAttrImplements;
    if (options & NL_ExcludeMacroExpansions)
      flags |= NominalTypeDecl::LookupDirectFlags::ExcludeMacroExpansions;
    if (options & NL_ABIProviding)
      flags |= NominalTypeDecl::LookupDirectFlags::ABIProviding;

    // Note that the source loc argument doesn't matter, because excluding
    // macro expansions is already propagated through the lookup flags above.
    for (auto decl : current->lookupDirect(member.getFullName(),
                                           SourceLoc(), flags)) {
      // If we're performing a type lookup, don't even attempt to validate
      // the decl if its not a type.
      if ((options & NL_OnlyTypes) && !isa<TypeDecl>(decl))
        continue;

      // If we're performing a macro lookup, don't even attempt to validate
      // the decl if its not a macro.
      if ((options & NL_OnlyMacros) && !isa<MacroDecl>(decl))
        continue;

      if (isAcceptableLookupResult(DC, options, decl, onlyCompleteObjectInits,
                                   requireImport))
        decls.push_back(decl);
    }

    // Visit superclass.
    if (auto classDecl = dyn_cast<ClassDecl>(current)) {
      // If we're looking for initializers, only look at the superclass if the
      // current class permits inheritance. Even then, only find complete
      // object initializers.
      bool visitSuperclass = true;
      if (member.getBaseName().isConstructor()) {
        if (classDecl->inheritsSuperclassInitializers())
          onlyCompleteObjectInits = true;
        else
          visitSuperclass = false;
      }

      if (visitSuperclass) {
        if (auto superclassDecl = classDecl->getSuperclassDecl())
          if (visited.insert(superclassDecl).second)
            stack.push_back(superclassDecl);
      }
    }

    // Qualified name lookup can find generic value parameters.
    auto gpList = current->getGenericParams();

    // .. But not in type contexts (yet)
    if (!(options & NL_OnlyTypes) && gpList && !member.isSpecial()) {
      auto gp = gpList->lookUpGenericParam(member.getBaseIdentifier());

      if (gp && gp->isValue()) {
        decls.push_back(gp);
      }
    }

    // If we're not looking at a protocol and we're not supposed to
    // visit the protocols that this type conforms to, skip the next
    // step.
    if (!wantProtocolMembers && !currentIsProtocol)
      continue;

    if (auto *protoDecl = dyn_cast<ProtocolDecl>(current)) {
      // If we haven't seen a class declaration yet, look into the protocol.
      if (!sawClassDecl) {
        if (auto superclassDecl = protoDecl->getSuperclassDecl()) {
          visited.insert(superclassDecl);
          stack.push_back(superclassDecl);
        }
      }

      // Collect inherited protocols.
      for (auto inheritedProto : protoDecl->getInheritedProtocols()) {
        addNominalType(inheritedProto);
      }
    } else {
      // Collect the protocols to which the nominal type conforms.
      for (auto proto : current->getAllProtocols()) {
        if (visited.insert(proto).second) {
          stack.push_back(proto);
        }
      }

      // For a class, we don't need to visit the protocol members of the
      // superclass: that's already handled.
      if (isa<ClassDecl>(current))
        wantProtocolMembers = false;
    }
  }

  pruneLookupResultSet(DC, options, member.getModuleSelector(), decls);
  if (auto *debugClient = DC->getParentModule()->getDebugClient()) {
    debugClient->finishLookupInNominals(DC, typeDecls, member.getFullName(),
                                        options, decls);
  }

  return decls;
}

bool DeclContext::lookupQualified(ModuleDecl *module, DeclNameRef member,
                                  SourceLoc loc, NLOptions options,
                                  SmallVectorImpl<ValueDecl *> &decls) const {
  assert(decls.empty() && "additive lookup not supported");
  ModuleQualifiedLookupRequest req{this, module, member, loc, options};
  decls = evaluateOrDefault(getASTContext().evaluator, req, {});
  return !decls.empty();
}

QualifiedLookupResult
ModuleQualifiedLookupRequest::evaluate(Evaluator &eval, const DeclContext *DC,
                                       ModuleDecl *module, DeclNameRef member,
                                       NLOptions options) const {
  using namespace namelookup;
  QualifiedLookupResult decls;

  auto kind = (options & NL_OnlyTypes ? ResolutionKind::TypesOnly
               : options & NL_OnlyMacros ? ResolutionKind::MacrosOnly
               : ResolutionKind::Overloadable);
  auto topLevelScope = DC->getModuleScopeContext();
  if (module == topLevelScope->getParentModule()) {
    lookupInModule(module, member.getFullName(), member.hasModuleSelector(),
                   decls, NLKind::QualifiedLookup, kind, topLevelScope,
                   SourceLoc(), options);
  } else {
    // Note: This is a lookup into another module. Unless we're compiling
    // multiple modules at once, or if the other module re-exports this one,
    // it shouldn't be possible to have a dependency from that module on
    // anything in this one.

    // Perform the lookup in all imports of this module.
    auto &ctx = DC->getASTContext();
    auto accessPaths = ctx.getImportCache().getAllVisibleAccessPaths(
        module, topLevelScope);
    if (llvm::any_of(accessPaths,
                     [&](ImportPath::Access accessPath) {
                       return accessPath.matches(member.getFullName());
                     })) {
      lookupInModule(module, member.getFullName(), member.hasModuleSelector(),
                     decls, NLKind::QualifiedLookup, kind, topLevelScope,
                     SourceLoc(), options);
    }
  }

  pruneLookupResultSet(DC, options, member.getModuleSelector(), decls);

  if (auto *debugClient = DC->getParentModule()->getDebugClient()) {
    debugClient->finishLookupInModule(DC, module, member.getFullName(),
                                      options, decls);
  }

  return decls;
}

QualifiedLookupResult
AnyObjectLookupRequest::evaluate(Evaluator &evaluator, const DeclContext *dc,
                                 DeclNameRef member, NLOptions options) const {
  using namespace namelookup;
  QualifiedLookupResult decls;

  // Type-only and macro lookup won't find anything on AnyObject.
  // AnyObject doesn't provide ABI.
  if (options & (NL_OnlyTypes | NL_OnlyMacros | NL_ABIProviding))
    return decls;

  // Collect all of the visible declarations.
  SmallVector<ValueDecl *, 4> allDecls;
  for (auto import : namelookup::getAllImports(dc)) {
    import.importedModule->lookupClassMember(import.accessPath,
                                             member.getFullName(), allDecls);
  }

  /// Whether to enforce MemberImportVisibility import restrictions.
  bool requireImport = shouldRequireImportsInContext(dc);

  // For each declaration whose context is not something we've
  // already visited above, add it to the list of declarations.
  llvm::SmallPtrSet<ValueDecl *, 4> knownDecls;
  for (auto decl : allDecls) {
    // If the declaration is not @objc, it cannot be called dynamically.
    if (!decl->isObjC())
      continue;

    // If the declaration is objc_direct, it cannot be called dynamically.
    if (auto clangDecl = decl->getClangDecl()) {
      if (auto objCMethod = dyn_cast<clang::ObjCMethodDecl>(clangDecl)) {
        if (objCMethod->isDirectMethod())
          continue;
      } else if (auto objCProperty = dyn_cast<clang::ObjCPropertyDecl>(clangDecl)) {
        if (objCProperty->isDirectProperty())
          continue;
      }
    }

    // If the declaration has an override, name lookup will also have
    // found the overridden method. Skip this declaration, because we
    // prefer the overridden method.
    if (decl->getOverriddenDecl())
      continue;

    assert(decl->getDeclContext()->isTypeContext() &&
           "Couldn't find nominal type?");

    // If we didn't see this declaration before, and it's an acceptable
    // result, add it to the list.
    if (knownDecls.insert(decl).second &&
        isAcceptableLookupResult(dc, options, decl,
                                 /*onlyCompleteObjectInits=*/false,
                                 requireImport))
      decls.push_back(decl);
  }

  pruneLookupResultSet(dc, options, member.getModuleSelector(), decls);
  if (auto *debugClient = dc->getParentModule()->getDebugClient()) {
    debugClient->finishLookupInAnyObject(dc, member.getFullName(), options,
                                         decls);
  }
  return decls;
}

void DeclContext::lookupAllObjCMethods(
       ObjCSelector selector,
       SmallVectorImpl<AbstractFunctionDecl *> &results) const {
  // Collect all of the methods with this selector.
  for (auto import : namelookup::getAllImports(this)) {
    import.importedModule->lookupObjCMethods(selector, results);
  }

  // Filter out duplicates.
  llvm::SmallPtrSet<AbstractFunctionDecl *, 8> visited;
  results.erase(
    std::remove_if(results.begin(), results.end(),
                   [&](AbstractFunctionDecl *func) -> bool {
                     return !visited.insert(func).second;
                   }),
    results.end());
}

void DeclContext::lookupAvailabilityDomains(
    Identifier identifier, SmallVectorImpl<AvailabilityDomain> &results) const {
  if (auto builtinDomain =
          AvailabilityDomain::builtinDomainForString(identifier.str(), this)) {
    results.push_back(*builtinDomain);
    return;
  }

  // FIXME: [availability] Find the file/module scope decl context and look up
  // the domain in that context using a request to cache the results.
  for (auto import : namelookup::getAllImports(this)) {
    import.importedModule->lookupAvailabilityDomains(identifier, results);
  }
}

/// Given a set of type declarations, find all of the nominal type declarations
/// that they reference, looking through typealiases as appropriate.
static TinyPtrVector<NominalTypeDecl *>
resolveTypeDeclsToNominal(Evaluator &evaluator,
                          ASTContext &ctx,
                          ArrayRef<TypeDecl *> typeDecls,
                          ResolveToNominalOptions options,
                          SmallVectorImpl<ModuleDecl *> &modulesFound,
                          bool &anyObject,
                          llvm::SmallPtrSetImpl<TypeAliasDecl *> &typealiases) {
  SmallPtrSet<NominalTypeDecl *, 4> knownNominalDecls;
  TinyPtrVector<NominalTypeDecl *> nominalDecls;
  auto addNominalDecl = [&](NominalTypeDecl *nominal) {
    if (knownNominalDecls.insert(nominal).second)
      nominalDecls.push_back(nominal);
  };

  for (auto typeDecl : typeDecls) {
    // Nominal type declarations get copied directly.
    if (auto nominalDecl = dyn_cast<NominalTypeDecl>(typeDecl)) {
      // ... unless it's the special Builtin.TheTupleType that we return
      // when resolving a TupleTypeRepr, and the caller isn't asking for
      // that.
      if (!options.contains(ResolveToNominalFlags::AllowTupleType) &&
          isa<BuiltinTupleDecl>(nominalDecl)) {
        continue;
      }

      addNominalDecl(nominalDecl);
      continue;
    }

    // Recursively resolve typealiases.
    if (auto typealias = dyn_cast<TypeAliasDecl>(typeDecl)) {
      // FIXME: Ad hoc recursion breaking, so we don't look through the
      // same typealias multiple times.
      if (!typealiases.insert(typealias).second)
        continue;

      auto underlyingTypeReferences = evaluateOrDefault(evaluator,
        UnderlyingTypeDeclsReferencedRequest{typealias}, {});

      auto underlyingNominalReferences
        = resolveTypeDeclsToNominal(evaluator, ctx, underlyingTypeReferences.first,
                                    options, modulesFound, anyObject, typealiases);
      std::for_each(underlyingNominalReferences.begin(),
                    underlyingNominalReferences.end(),
                    addNominalDecl);

      // Recognize Swift.AnyObject directly.
      if (typealias->getName().is("AnyObject")) {
        // Type version: an empty class-bound existential.
        if (auto type = typealias->getUnderlyingType()) {
          if (type->isAnyObject())
            anyObject = true;
        }
        // TypeRepr version: Builtin.AnyObject
        else if (auto *qualIdentTR = dyn_cast_or_null<QualifiedIdentTypeRepr>(
                     typealias->getUnderlyingTypeRepr())) {
          if (!qualIdentTR->hasGenericArgList() &&
              qualIdentTR->getNameRef().isSimpleName("AnyObject") &&
              qualIdentTR->getBase()->isSimpleUnqualifiedIdentifier(
                  "Builtin")) {
            anyObject = true;
          }
        }
      }

      continue;
    }

    // Keep track of modules we see.
    if (auto module = dyn_cast<ModuleDecl>(typeDecl)) {
      modulesFound.push_back(module);
      continue;
    }

    // Make sure we didn't miss some interesting kind of type declaration.
    assert(isa<GenericTypeParamDecl>(typeDecl) ||
           isa<AssociatedTypeDecl>(typeDecl));
  }

  return nominalDecls;
}

static TinyPtrVector<NominalTypeDecl *>
resolveTypeDeclsToNominal(Evaluator &evaluator,
                          ASTContext &ctx,
                          ArrayRef<TypeDecl *> typeDecls,
                          ResolveToNominalOptions options,
                          SmallVectorImpl<ModuleDecl *> &modulesFound,
                          bool &anyObject) {
  llvm::SmallPtrSet<TypeAliasDecl *, 4> typealiases;
  return resolveTypeDeclsToNominal(evaluator, ctx, typeDecls, options,
                                   modulesFound, anyObject, typealiases);
}

/// Perform unqualified name lookup for types at the given location.
static DirectlyReferencedTypeDecls directReferencesForUnqualifiedTypeLookup(
    DeclNameRef name, SourceLoc loc, DeclContext *dc,
    LookupOuterResults lookupOuter,
    DirectlyReferencedTypeLookupOptions typeLookupOptions) {
  UnqualifiedLookupOptions options = UnqualifiedLookupFlags::TypeLookup;
  if (typeLookupOptions.contains(
          DirectlyReferencedTypeLookupFlags::AllowProtocolMembers))
    options |= UnqualifiedLookupFlags::AllowProtocolMembers;
  if (lookupOuter == LookupOuterResults::Included)
    options |= UnqualifiedLookupFlags::IncludeOuterResults;

  if (typeLookupOptions.contains(
          DirectlyReferencedTypeLookupFlags::AllowUsableFromInline))
    options |= UnqualifiedLookupFlags::IncludeUsableFromInline;

  if (typeLookupOptions.contains(
          DirectlyReferencedTypeLookupFlags::IgnoreMissingImports))
    options |= UnqualifiedLookupFlags::IgnoreMissingImports;

  if (typeLookupOptions.contains(
          DirectlyReferencedTypeLookupFlags::ExcludeMacroExpansions))
    options |= UnqualifiedLookupFlags::ExcludeMacroExpansions;

  // Manually exclude macro expansions here since the source location
  // is overridden below.
  if (namelookup::isInMacroArgument(dc->getParentSourceFile(), loc))
    options |= UnqualifiedLookupFlags::ExcludeMacroExpansions;

  // If the source location is located anywhere within an `@abi` attribute, look
  // up using ABI names.
  if (namelookup::isInABIAttr(dc->getParentSourceFile(), loc))
    options |= UnqualifiedLookupFlags::ABIProviding;

  // In a protocol or protocol extension, the 'where' clause can refer to
  // associated types without 'Self' qualification:
  //
  // protocol MyProto where AssocType : Q { ... }
  //
  // extension MyProto where AssocType == Int { ... }
  //
  // To avoid cycles when resolving the right-hand side, we perform the
  // lookup in the parent context (for a protocol), or a special mode where
  // we disregard 'Self' requirements (for a protocol extension).
  if (typeLookupOptions.contains(
          DirectlyReferencedTypeLookupFlags::RHSOfSelfRequirement)) {
    if (dc->getExtendedProtocolDecl())
      options |= UnqualifiedLookupFlags::DisregardSelfBounds;
    else {
      dc = dc->getModuleScopeContext();
      loc = SourceLoc();
    }
  }

  DirectlyReferencedTypeDecls results;

  auto &ctx = dc->getASTContext();
  auto descriptor = UnqualifiedLookupDescriptor(name, dc, loc, options);
  auto lookup = evaluateOrDefault(ctx.evaluator,
                                  UnqualifiedLookupRequest{descriptor}, {});

  unsigned nominalTypeDeclCount = 0;
  for (const auto &result : lookup.allResults()) {
    auto typeDecl = cast<TypeDecl>(result.getValueDecl());

    if (isa<NominalTypeDecl>(typeDecl))
      nominalTypeDeclCount++;

    results.first.push_back(typeDecl);
  }

  // If we saw multiple nominal type declarations with the same name,
  // the result of the lookup is definitely ambiguous.
  if (nominalTypeDeclCount > 1)
    results.first.clear();

  return results;
}

/// Perform qualified name lookup for types.
static llvm::TinyPtrVector<TypeDecl *> directReferencesForQualifiedTypeLookup(
    Evaluator &evaluator, ASTContext &ctx, ArrayRef<TypeDecl *> baseTypes,
    DeclNameRef name, DeclContext *dc, SourceLoc loc,
    DirectlyReferencedTypeLookupOptions typeLookupOptions) {
  llvm::TinyPtrVector<TypeDecl *> result;
  auto addResults = [&result](ArrayRef<ValueDecl *> found){
    for (auto decl : found){
      assert(isa<TypeDecl>(decl) &&
             "Lookup should only have found type declarations");
      result.push_back(cast<TypeDecl>(decl));
    }
  };

  {
    // Look into the base types.
    SmallVector<ValueDecl *, 4> members;
    auto options = NL_RemoveNonVisible | NL_OnlyTypes;

    if (typeLookupOptions.contains(
            DirectlyReferencedTypeLookupFlags::AllowUsableFromInline))
      options |= NL_IncludeUsableFromInline;

    if (typeLookupOptions.contains(
            DirectlyReferencedTypeLookupFlags::IgnoreMissingImports))
      options |= NL_IgnoreMissingImports;

    if (typeLookupOptions.contains(
            DirectlyReferencedTypeLookupFlags::ExcludeMacroExpansions))
      options |= NL_ExcludeMacroExpansions;

    // Look through the type declarations we were given, resolving them down
    // to nominal type declarations, module declarations, and
    SmallVector<ModuleDecl *, 2> moduleDecls;
    bool anyObject = false;
    auto nominalTypeDecls =
      resolveTypeDeclsToNominal(ctx.evaluator, ctx, baseTypes,
                                ResolveToNominalOptions(),
                                moduleDecls, anyObject);

    dc->lookupQualified(nominalTypeDecls, name, loc, options, members);

    // Search all of the modules.
    for (auto module : moduleDecls) {
      auto innerOptions = options;
      innerOptions &= ~NL_RemoveOverridden;
      innerOptions &= ~NL_RemoveNonVisible;
      SmallVector<ValueDecl *, 4> moduleMembers;
      dc->lookupQualified(module, name, loc, innerOptions, moduleMembers);
      members.append(moduleMembers.begin(), moduleMembers.end());
    }

    addResults(members);
  }

  return result;
}

/// Determine the types directly referenced by the given identifier type.
static DirectlyReferencedTypeDecls directReferencesForDeclRefTypeRepr(
    Evaluator &evaluator, ASTContext &ctx, DeclRefTypeRepr *repr,
    DeclContext *dc, DirectlyReferencedTypeLookupOptions options) {
  if (auto *qualIdentTR = dyn_cast<QualifiedIdentTypeRepr>(repr)) {
    auto result = directReferencesForTypeRepr(
        evaluator, ctx, qualIdentTR->getBase(), dc, options);

    // For a qualified identifier, perform qualified name lookup.
    result.first = directReferencesForQualifiedTypeLookup(
        evaluator, ctx, result.first, repr->getNameRef(), dc, repr->getLoc(),
        options);

    return result;
  }

  // For an unqualified identifier, perform unqualified name lookup.
  return directReferencesForUnqualifiedTypeLookup(
      repr->getNameRef(), repr->getLoc(), dc, LookupOuterResults::Excluded,
      options);
}

static DirectlyReferencedTypeDecls
directReferencesForTypeRepr(Evaluator &evaluator, ASTContext &ctx,
                            TypeRepr *typeRepr, DeclContext *dc,
                            DirectlyReferencedTypeLookupOptions options) {
  DirectlyReferencedTypeDecls result;

  switch (typeRepr->getKind()) {
  case TypeReprKind::Array:
    result.first.push_back(ctx.getArrayDecl());
    return result;

  case TypeReprKind::InlineArray:
    result.first.push_back(ctx.getInlineArrayDecl());
    return result;

  case TypeReprKind::Attributed: {
    auto attributed = cast<AttributedTypeRepr>(typeRepr);
    return directReferencesForTypeRepr(evaluator, ctx,
                                       attributed->getTypeRepr(), dc, options);
  }

  case TypeReprKind::Isolated: {
    auto isolated = cast<IsolatedTypeRepr>(typeRepr);
    return directReferencesForTypeRepr(evaluator, ctx,
                                       isolated->getBase(), dc, options);
  }

  case TypeReprKind::CallerIsolated: {
    auto callerIsolated = cast<CallerIsolatedTypeRepr>(typeRepr);
    return directReferencesForTypeRepr(evaluator, ctx,
                                       callerIsolated->getBase(), dc, options);
  }

  case TypeReprKind::Composition: {
    auto composition = cast<CompositionTypeRepr>(typeRepr);
    for (auto component : composition->getTypes()) {
      auto componentResult =
          directReferencesForTypeRepr(evaluator, ctx, component, dc, options);
      result.first.insert(result.first.end(),
                          componentResult.first.begin(),
                          componentResult.first.end());

      // Merge inverses.
      result.second.insertAll(componentResult.second);
    }
    return result;
  }

  case TypeReprKind::QualifiedIdent:
  case TypeReprKind::UnqualifiedIdent:
    return directReferencesForDeclRefTypeRepr(
        evaluator, ctx, cast<DeclRefTypeRepr>(typeRepr), dc, options);

  case TypeReprKind::Dictionary:
    result.first.push_back(ctx.getDictionaryDecl());
    return result;

  case TypeReprKind::Tuple: {
    auto tupleRepr = cast<TupleTypeRepr>(typeRepr);
    if (tupleRepr->isParenType()) {
      result = directReferencesForTypeRepr(
          evaluator, ctx, tupleRepr->getElementType(0), dc, options);
    } else {
      result.first.push_back(ctx.getBuiltinTupleDecl());
    }
    return result;
  }

  case TypeReprKind::Vararg: {
    auto packExpansionRepr = cast<VarargTypeRepr>(typeRepr);
    return directReferencesForTypeRepr(
        evaluator, ctx, packExpansionRepr->getElementType(), dc, options);
  }

  case TypeReprKind::PackExpansion: {
    auto packExpansionRepr = cast<PackExpansionTypeRepr>(typeRepr);
    return directReferencesForTypeRepr(
        evaluator, ctx, packExpansionRepr->getPatternType(), dc, options);
  }

  case TypeReprKind::PackElement: {
    auto packReferenceRepr = cast<PackElementTypeRepr>(typeRepr);
    return directReferencesForTypeRepr(
        evaluator, ctx, packReferenceRepr->getPackType(), dc, options);
  }

  case TypeReprKind::Inverse: {
    // If ~P references a protocol P with a known inverse kind, record it in
    // our set of inverses, otherwise just ignore it. We'll diagnose it later.
    auto *inverseRepr = cast<InverseTypeRepr>(typeRepr);
    auto innerResult = directReferencesForTypeRepr(
        evaluator, ctx, inverseRepr->getConstraint(), dc, options);
    if (innerResult.first.size() == 1) {
      if (auto *proto = dyn_cast<ProtocolDecl>(innerResult.first[0])) {
        if (auto ip = proto->getInvertibleProtocolKind()) {
          result.second.insert(*ip);
        }
      }
    }

    return result;
  }

  case TypeReprKind::Error:
  case TypeReprKind::Function:
  case TypeReprKind::Ownership:
  case TypeReprKind::CompileTimeLiteral:
  case TypeReprKind::ConstValue:
  case TypeReprKind::Metatype:
  case TypeReprKind::Protocol:
  case TypeReprKind::SILBox:
  case TypeReprKind::Placeholder:
  case TypeReprKind::Pack:
  case TypeReprKind::OpaqueReturn:
  case TypeReprKind::NamedOpaqueReturn:
  case TypeReprKind::Existential:
  case TypeReprKind::LifetimeDependent:
  case TypeReprKind::Sending:
  case TypeReprKind::Integer:
    return result;

  case TypeReprKind::Fixed:
    llvm_unreachable("Cannot get fixed TypeReprs in name lookup");
  case TypeReprKind::Self:
    llvm_unreachable("Cannot get fixed SelfTypeRepr in name lookup");

  case TypeReprKind::Optional:
  case TypeReprKind::ImplicitlyUnwrappedOptional:
    result.first.push_back(ctx.getOptionalDecl());
    return result;
  }
  llvm_unreachable("unhandled kind");
}

static DirectlyReferencedTypeDecls directReferencesForType(Type type) {
  DirectlyReferencedTypeDecls result;

  // If it's a typealias, return that.
  if (auto aliasType = dyn_cast<TypeAliasType>(type.getPointer())) {
    result.first.push_back(aliasType->getDecl());
    return result;
  }

  // If there is a generic declaration, return it.
  if (auto genericDecl = type->getAnyGeneric()) {
    result.first.push_back(genericDecl);
    return result;
  }

  if (type->is<TupleType>()) {
    result.first.push_back(type->getASTContext().getBuiltinTupleDecl());
    return result;
  }

  if (auto *protoType = type->getAs<ProtocolType>()) {
    result.first.push_back(protoType->getDecl());
    return result;
  }

  if (auto *compositionType = type->getAs<ProtocolCompositionType>()) {
    for (auto member : compositionType->getMembers()) {
      auto componentResult = directReferencesForType(member);
      result.first.insert(result.first.end(),
                          componentResult.first.begin(),
                          componentResult.first.end());

      // Merge inverses from each member recursively.
      result.second.insertAll(componentResult.second);
    }

    // Merge inverses attached to the composition itself.
    result.second.insertAll(compositionType->getInverses());
    return result;
  }

  if (auto *paramType = type->getAs<ParameterizedProtocolType>()) {
    return directReferencesForType(paramType->getBaseType());
  }

  if (auto *existentialType = type->getAs<ExistentialType>()) {
    return directReferencesForType(existentialType->getConstraintType());
  }

  return result;
}

DirectlyReferencedTypeDecls InheritedDeclsReferencedRequest::evaluate(
    Evaluator &evaluator,
    llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
    unsigned index) const {

  // Prefer syntactic information when we have it.
  const InheritedEntry &typeLoc = InheritedTypes(decl).getEntry(index);
  if (auto typeRepr = typeLoc.getTypeRepr()) {
    // Figure out the context in which name lookup will occur.
    DeclContext *dc;
    if (auto typeDecl = decl.dyn_cast<const TypeDecl *>())
      dc = typeDecl->getInnermostDeclContext();
    else
      dc = (DeclContext *)cast<const ExtensionDecl *>(decl);

    // If looking at a protocol's inheritance list,
    // do not look at protocol members to avoid circularity.
    // Protocols cannot inherit from any protocol members anyway.
    DirectlyReferencedTypeLookupOptions options;
    if (dc->getSelfProtocolDecl() == nullptr) {
      options |= DirectlyReferencedTypeLookupFlags::AllowProtocolMembers;
    }

    return directReferencesForTypeRepr(evaluator, dc->getASTContext(), typeRepr,
                                       const_cast<DeclContext *>(dc), options);
  }

  // Fall back to semantic types.
  // FIXME: In the long run, we shouldn't need this. Non-syntactic results
  // should be cached.
  if (auto type = typeLoc.getType()) {
    return directReferencesForType(type);
  }

  return { };
}

DirectlyReferencedTypeDecls UnderlyingTypeDeclsReferencedRequest::evaluate(
    Evaluator &evaluator,
    TypeAliasDecl *typealias) const {
  // Prefer syntactic information when we have it.
  if (auto typeRepr = typealias->getUnderlyingTypeRepr()) {
    return directReferencesForTypeRepr(
        evaluator, typealias->getASTContext(), typeRepr, typealias,
        defaultDirectlyReferencedTypeLookupOptions);
  }

  // Fall back to semantic types.
  // FIXME: In the long run, we shouldn't need this. Non-syntactic results
  // should be cached.
  if (auto type = typealias->getUnderlyingType()) {
    return directReferencesForType(type);
  }

  return { };
}

/// Evaluate a superclass declaration request.
ClassDecl *
SuperclassDeclRequest::evaluate(Evaluator &evaluator,
                                NominalTypeDecl *subject) const {
  auto &Ctx = subject->getASTContext();

  // Protocols may get their superclass bound from a `where Self : Superclass`
  // clause.
  if (auto *proto = dyn_cast<ProtocolDecl>(subject)) {
    assert(!proto->wasDeserialized());

    auto selfBounds = getSelfBoundsFromWhereClause(proto);
    for (auto inheritedNominal : selfBounds.decls)
      if (auto classDecl = dyn_cast<ClassDecl>(inheritedNominal))
        return classDecl;
  }

  for (unsigned i : subject->getInherited().getIndices()) {
    // Find the inherited declarations referenced at this position.
    auto inheritedTypes = evaluateOrDefault(evaluator,
      InheritedDeclsReferencedRequest{subject, i}, {});

    // Resolve those type declarations to nominal type declarations.
    SmallVector<ModuleDecl *, 2> modulesFound;
    bool anyObject = false;
    auto inheritedNominalTypes
      = resolveTypeDeclsToNominal(evaluator, Ctx,
                                  inheritedTypes.first,
                                  ResolveToNominalOptions(),
                                  modulesFound, anyObject);

    // Look for a class declaration.
    ClassDecl *superclass = nullptr;
    for (auto inheritedNominal : inheritedNominalTypes) {
      if (auto classDecl = dyn_cast<ClassDecl>(inheritedNominal)) {
        superclass = classDecl;
        break;
      }
    }

    // If we found a superclass, ensure that we don't have a circular
    // inheritance hierarchy by evaluating its superclass. This forces the
    // diagnostic at this point and then suppresses the superclass failure.
    if (superclass) {
      if (evaluateOrDefault(Ctx.evaluator,
                            SuperclassDeclRequest{superclass},
                            superclass) == superclass) {
        return nullptr;
      }

      return superclass;
    }
  }

  return nullptr;
}

ArrayRef<ProtocolDecl *>
InheritedProtocolsRequest::evaluate(Evaluator &evaluator,
                                    ProtocolDecl *PD) const {
  auto &ctx = PD->getASTContext();

  llvm::SmallSetVector<ProtocolDecl *, 2> inherited;

  assert(!PD->wasDeserialized());

  InvertibleProtocolSet inverses;
  bool anyObject = false;
  for (const auto &found :
       getDirectlyInheritedNominalTypeDecls(PD, inverses, anyObject)) {
    auto proto = dyn_cast<ProtocolDecl>(found.Item);
    if (proto && proto != PD)
      inherited.insert(proto);
  }

  // Apply inverses.
  bool skipInverses = false;

  // ... except for these protocols, so that Copyable does not have to
  // inherit ~Copyable, etc.
  if (auto kp = PD->getKnownProtocolKind()) {
    switch (*kp) {
    case KnownProtocolKind::Sendable:
    case KnownProtocolKind::Copyable:
    case KnownProtocolKind::Escapable:
      skipInverses = true;
      break;

    default:
      break;
    }
  }

  if (!skipInverses) {
    for (auto ip : InvertibleProtocolSet::allKnown()) {
      // Unless the user wrote ~P in the syntactic inheritance clause, the
      // semantic inherited list includes P.
      if (!inverses.contains(ip))
        inherited.insert(ctx.getProtocol(getKnownProtocolKind(ip)));
    }
  }

  return ctx.AllocateCopy(inherited.getArrayRef());
}

ArrayRef<ProtocolDecl *>
AllInheritedProtocolsRequest::evaluate(Evaluator &evaluator,
                                       ProtocolDecl *PD) const {
  llvm::SmallSetVector<ProtocolDecl *, 2> result;

  PD->walkInheritedProtocols([&](ProtocolDecl *inherited) {
    if (inherited != PD)
      result.insert(inherited);
    return TypeWalker::Action::Continue;
  });

  return PD->getASTContext().AllocateCopy(result.getArrayRef());
}

ArrayRef<ValueDecl *>
ProtocolRequirementsRequest::evaluate(Evaluator &evaluator,
                                      ProtocolDecl *PD) const {
  SmallVector<ValueDecl *, 4> requirements;

  for (auto *member : PD->getABIMembers()) {
    auto *VD = dyn_cast<ValueDecl>(member);
    if (VD && VD->isProtocolRequirement())
      requirements.push_back(VD);
  }

  return PD->getASTContext().AllocateCopy(requirements);
}

NominalTypeDecl *ExtensionDecl::computeExtendedNominal(
    bool excludeMacroExpansions) const {
  auto typeRepr = getExtendedTypeRepr();
  if (!typeRepr) {
    // We must've seen 'extension { ... }' during parsing.
    return nullptr;
  }

  ASTContext &ctx = getASTContext();
  auto &evaluator = ctx.evaluator;
  auto options = defaultDirectlyReferencedTypeLookupOptions;

  if (isInSpecializeExtensionContext()) {
    options |= DirectlyReferencedTypeLookupFlags::AllowUsableFromInline;
  }

  if (excludeMacroExpansions) {
    options |= DirectlyReferencedTypeLookupFlags::ExcludeMacroExpansions;
  }

  DirectlyReferencedTypeDecls referenced = directReferencesForTypeRepr(
      evaluator, ctx, typeRepr, getParent(), options);

  // If there were no results, expand the lookup to include members that are
  // inaccessible due to missing imports. The missing imports will be diagnosed
  // elsewhere.
  if (referenced.first.empty() &&
      ctx.LangOpts.hasFeature(Feature::MemberImportVisibility,
                              /*allowMigration=*/true)) {
    options |= DirectlyReferencedTypeLookupFlags::IgnoreMissingImports;
    referenced = directReferencesForTypeRepr(evaluator, ctx, typeRepr,
                                             getParent(), options);
  }

  // Resolve those type declarations to nominal type declarations.
  SmallVector<ModuleDecl *, 2> modulesFound;
  bool anyObject = false;
  auto nominalTypes
    = resolveTypeDeclsToNominal(evaluator, ctx, referenced.first,
                                ResolveToNominalFlags::AllowTupleType,
                                modulesFound, anyObject);

  // If there is more than 1 element, we will emit a warning or an error
  // elsewhere, so don't handle that case here.
  if (nominalTypes.empty())
    return nullptr;

  auto *result = nominalTypes[0];

  // Tuple extensions are experimental, if the feature isn't enabled let's not
  // bind this extension at all. This fixes a bunch of crashers that we don't
  // yet properly handle with the feature enabled.
  if (isa<BuiltinTupleDecl>(result) &&
      !ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
    return nullptr;
  }

  return result;
}

NominalTypeDecl *
ExtendedNominalRequest::evaluate(Evaluator &evaluator,
                                 const ExtensionDecl *ext) const {
  ASSERT(ext->canNeverBeBound() && "Should have been bound by bindExtensions");
  return ext->computeExtendedNominal();
}

/// Whether there are only associated types in the set of declarations.
static bool declsAreAssociatedTypes(ArrayRef<TypeDecl *> decls) {
  if (decls.empty())
    return false;

  for (auto decl : decls) {
    if (!isa<AssociatedTypeDecl>(decl))
      return false;
  }

  return true;
}

/// Verify there is at least one protocols in the set of declarations.
static bool declsAreProtocols(ArrayRef<TypeDecl *> decls) {
  if (decls.empty())
    return false;  // Below, check outer type repr is a protocol, if not bail early
  return llvm::any_of(decls, [&](const TypeDecl *decl) {
    if (auto *alias = dyn_cast<TypeAliasDecl>(decl)) {
      auto ty = alias->getUnderlyingType();
      decl = ty->getNominalOrBoundGenericNominal();
      if (decl == nullptr || ty->is<ExistentialType>())
        return false;
    }
    return isa<ProtocolDecl>(decl);
  });
}

bool TypeRepr::isProtocolOrProtocolComposition(DeclContext *dc) {
  auto &ctx = dc->getASTContext();
  auto references = directReferencesForTypeRepr(
      ctx.evaluator, ctx, this, dc, defaultDirectlyReferencedTypeLookupOptions);
  return declsAreProtocols(references.first);
}

static GenericParamList *
createExtensionGenericParams(ASTContext &ctx,
                             ExtensionDecl *ext,
                             DeclContext *source) {
  // Collect generic parameters from all outer contexts.
  SmallVector<GenericParamList *, 2> allGenericParams;
  source->forEachGenericContext([&](GenericParamList *gpList) {
    allGenericParams.push_back(gpList->clone(ext));
  });

  GenericParamList *toParams = nullptr;
  for (auto *gpList : llvm::reverse(allGenericParams)) {
    gpList->setOuterParameters(toParams);
    toParams = gpList;
  }

  return toParams;
}

/// If the extended type is a generic typealias whose underlying type is
/// a tuple, the extension inherits the generic parameter list from the
/// typealias.
static GenericParamList *
createTupleExtensionGenericParams(ASTContext &ctx,
                                  ExtensionDecl *ext,
                                  TypeRepr *extendedTypeRepr) {
  DirectlyReferencedTypeDecls referenced = directReferencesForTypeRepr(
      ctx.evaluator, ctx, extendedTypeRepr, ext->getParent(),
      defaultDirectlyReferencedTypeLookupOptions);
  assert(referenced.second.empty() && "Implement me");
  if (referenced.first.size() != 1 || !isa<TypeAliasDecl>(referenced.first[0]))
    return nullptr;

  auto *typeAlias = cast<TypeAliasDecl>(referenced.first[0]);
  if (!typeAlias->hasGenericParamList())
    return nullptr;

  return createExtensionGenericParams(ctx, ext, typeAlias);
}

CollectedOpaqueReprs swift::collectOpaqueTypeReprs(TypeRepr *r, ASTContext &ctx,
                                                   DeclContext *d) {
  class Walker : public ASTWalker {
    CollectedOpaqueReprs &Reprs;
    ASTContext &Ctx;
    DeclContext *dc;

  public:
    explicit Walker(CollectedOpaqueReprs &reprs, ASTContext &ctx, DeclContext *d) : Reprs(reprs), Ctx(ctx), dc(d) {}

    /// Walk everything that's available.
    MacroWalking getMacroWalkingBehavior() const override {
      return MacroWalking::ArgumentsAndExpansion;
    }

    PreWalkAction walkToTypeReprPre(TypeRepr *repr) override {

      // Don't allow variadic opaque parameter or return types.
      if (isa<PackExpansionTypeRepr>(repr) || isa<VarargTypeRepr>(repr))
        return Action::SkipNode();

      if (auto opaqueRepr = dyn_cast<OpaqueReturnTypeRepr>(repr)) {
        Reprs.push_back(opaqueRepr);
        if (Ctx.LangOpts.hasFeature(Feature::ImplicitSome))
          return Action::SkipNode();
      }

      if (!Ctx.LangOpts.hasFeature(Feature::ImplicitSome))
        return Action::Continue();
      
      if (isa<ExistentialTypeRepr>(repr)) {
        return Action::SkipNode();
      } else if (auto composition = dyn_cast<CompositionTypeRepr>(repr)) {
        if (!composition->isTypeReprAny())
          Reprs.push_back(composition);
        return Action::SkipNode();
      } else if (isa<DeclRefTypeRepr>(repr)) {
        // We only care about the type of an outermost member type
        // representation. For example, in `A<T>.B.C<U>`, check `C` and generic
        // arguments `U` and `T`, but not `A` or `B`.
        if (auto *parentQualIdentTR = dyn_cast_or_null<QualifiedIdentTypeRepr>(
                Parent.getAsTypeRepr())) {
          if (repr == parentQualIdentTR->getBase()) {
            return Action::Continue();
          }
        }

        if (repr->isProtocolOrProtocolComposition(dc))
          Reprs.push_back(repr);
      }
      return Action::Continue();
    }

  };

  CollectedOpaqueReprs reprs;
  r->walk(Walker(reprs, ctx, d));
  return reprs;
}

/// If there are opaque parameters in the given declaration, create the
/// generic parameters associated with them.
static SmallVector<GenericTypeParamDecl *, 2>
createOpaqueParameterGenericParams(GenericContext *genericContext, GenericParamList *parsedGenericParams) {
  ASTContext &ctx = genericContext->getASTContext();
    
  auto value = dyn_cast_or_null<ValueDecl>(genericContext->getAsDecl());
  if (!value)
    return { };

  // Functions, initializers, and subscripts can contain opaque parameters.
  // FIXME: What's wrong with allowing them in macro decls?
  if (isa<MacroDecl>(value)) {
    return { };
  }
  auto *params = value->getParameterList();
  if (!params) {
    return {};
  }

  // Look for parameters that have "some" types in them.
  unsigned index = parsedGenericParams ? parsedGenericParams->size() : 0;
  SmallVector<GenericTypeParamDecl *, 2> implicitGenericParams;
  auto dc = value->getInnermostDeclContext();
  for (auto param : *params) {
    auto typeRepr = param->getTypeRepr();
    if (!typeRepr)
      continue;

    // Plain protocols should imply 'some' with experimetal feature
    CollectedOpaqueReprs typeReprs;
    typeReprs = collectOpaqueTypeReprs(typeRepr, ctx, dc);

    for (auto repr : typeReprs) {
   
      // Allocate a new generic parameter to represent this opaque type.
      //
      // Note: Opaque parameters are always treated as
      // GenericTypeParamKind::Type right now. The opaque type representation
      // indicates it's an opaque parameter.
      auto *gp = GenericTypeParamDecl::createImplicit(
          dc, Identifier(), GenericTypeParamDecl::InvalidDepth, index++,
          GenericTypeParamKind::Type, repr, /*nameLoc*/ repr->getStartLoc());

      // Use the underlying constraint as the constraint on the generic parameter.
      //  The underlying constraint is only present for OpaqueReturnTypeReprs
      if (auto opaque = dyn_cast<OpaqueReturnTypeRepr>(repr)) {
              InheritedEntry inherited[1] = {
                  { TypeLoc(opaque->getConstraint()) }
              };
              gp->setInherited(ctx.AllocateCopy(inherited));
      } else {
            InheritedEntry inherited[1] = {
                { TypeLoc(repr) }
            };
            gp->setInherited(ctx.AllocateCopy(inherited));
      }
      implicitGenericParams.push_back(gp);
    }
  }

  return implicitGenericParams;
}

GenericParamList *
GenericParamListRequest::evaluate(Evaluator &evaluator, GenericContext *value) const {
  if (auto *tupleDecl = dyn_cast<BuiltinTupleDecl>(value)) {
    auto &ctx = value->getASTContext();

    // Builtin.TheTupleType has a single pack generic parameter: <each Element>
    auto *genericParam = GenericTypeParamDecl::createImplicit(
        tupleDecl->getDeclContext(), ctx.Id_Element, /*depth*/ 0, /*index*/ 0,
        GenericTypeParamKind::Pack);

    return GenericParamList::create(ctx, SourceLoc(), genericParam,
                                    SourceLoc());
  }

  if (auto *ext = dyn_cast<ExtensionDecl>(value)) {
    // Create the generic parameter list for the extension by cloning the
    // generic parameter lists of the nominal and any of its parent types.
    auto &ctx = value->getASTContext();
    auto *nominal = ext->getExtendedNominal();
    if (!nominal) {
      return nullptr;
    }

    // For a tuple extension, the generic parameter list comes from the
    // extended type alias.
    if (isa<BuiltinTupleDecl>(nominal)) {
      if (auto *extendedTypeRepr = ext->getExtendedTypeRepr()) {
        auto *genericParams = createTupleExtensionGenericParams(
            ctx, ext, extendedTypeRepr);
        if (genericParams)
          return genericParams;

        // Otherwise, just clone the generic parameter list of the
        // Builtin.TheTupleType. We'll diagnose later.
      }
    }

    auto *genericParams = createExtensionGenericParams(ctx, ext, nominal);

    // Protocol extensions need an inheritance clause due to how name lookup
    // is implemented.
    if (auto *proto = ext->getExtendedProtocolDecl()) {
      auto protoType = proto->getDeclaredInterfaceType();
      InheritedEntry selfInherited[1] = {
        InheritedEntry(TypeLoc::withoutLoc(protoType)) };
      genericParams->getParams().front()->setInherited(
        ctx.AllocateCopy(selfInherited));
    }

    // Set the depth of every generic parameter.
    unsigned depth = nominal->getGenericContextDepth();
    for (auto *outerParams = genericParams;
         outerParams != nullptr;
         outerParams = outerParams->getOuterParameters())
      outerParams->setDepth(depth--);

    return genericParams;
  }

  if (auto *proto = dyn_cast<ProtocolDecl>(value)) {
    // The generic parameter 'Self'.
    auto &ctx = value->getASTContext();
    auto selfId = ctx.Id_Self;
    auto selfDecl = GenericTypeParamDecl::createImplicit(
        proto, selfId, /*depth*/ 0, /*index*/ 0, GenericTypeParamKind::Type);
    auto protoType = proto->getDeclaredInterfaceType();
    InheritedEntry selfInherited[1] = {
      InheritedEntry(TypeLoc::withoutLoc(protoType)) };
    selfDecl->setInherited(ctx.AllocateCopy(selfInherited));
    selfDecl->setImplicit();

    // The generic parameter list itself.
    auto result = GenericParamList::create(ctx, SourceLoc(), selfDecl,
                                           SourceLoc());
    return result;
  }

  // AccessorDecl generic parameter list is the same of its storage
  // context.
  if (auto *AD = dyn_cast<AccessorDecl>(value)) {
    auto *GC = AD->getStorage()->getAsGenericContext();
    if (!GC)
      return nullptr;

    auto *GP = GC->getGenericParams();
    if (!GP)
      return nullptr;

    return GP->clone(AD->getDeclContext());
  }

  auto parsedGenericParams = value->getParsedGenericParams();

  // Create implicit generic parameters due to opaque parameters, if we need
  // them.
  auto implicitGenericParams =
      createOpaqueParameterGenericParams(value, parsedGenericParams);
  if (implicitGenericParams.empty())
    return parsedGenericParams;

  // If there were no parsed generic parameters, create a fully-implicit
  // generic parameter list.
  ASTContext &ctx = value->getASTContext();
  if (!parsedGenericParams) {
    return GenericParamList::create(
        ctx, SourceLoc(), implicitGenericParams, SourceLoc());
  }

  // Combine the existing generic parameters with the implicit ones.
  SmallVector<GenericTypeParamDecl *, 4> allGenericParams;
  allGenericParams.reserve(
      parsedGenericParams->size() + implicitGenericParams.size());
  allGenericParams.append(parsedGenericParams->begin(),
                          parsedGenericParams->end());
  allGenericParams.append(implicitGenericParams);
  return GenericParamList::create(
      ctx, parsedGenericParams->getLAngleLoc(), allGenericParams,
      parsedGenericParams->getWhereLoc(),
      parsedGenericParams->getRequirements(),
      parsedGenericParams->getRAngleLoc());
}

NominalTypeDecl *CustomAttrNominalRequest::evaluate(Evaluator &evaluator,
                                                    CustomAttr *attr) const {
  auto owner = attr->getOwner();
  auto *dc = owner.getDeclContext();

  // Look for names at module scope, so we don't trigger name lookup for
  // nested scopes. At this point, we're looking to see whether there are
  // any suitable macros. If we're preferring property wrappers we wait to see
  // if any property wrappers are in scope before returning.
  auto [module, macro] = attr->destructureMacroRef();
  auto moduleName = (module) ? module->getNameRef() : DeclNameRef();
  auto macroName = (macro) ? macro->getNameRef() : DeclNameRef();
  auto macros = namelookup::lookupMacros(dc, moduleName, macroName,
                                         getAttachedMacroRoles());
  auto shouldPreferPropWrapper = attr->shouldPreferPropertyWrapperOverMacro();
  if (!macros.empty() && !shouldPreferPropWrapper)
    return nullptr;

  // Find the types referenced by the custom attribute.
  auto &ctx = dc->getASTContext();
  DirectlyReferencedTypeDecls decls;
  if (auto *typeRepr = attr->getTypeRepr()) {
    decls =
        directReferencesForTypeRepr(evaluator, ctx, typeRepr, dc,
                                    defaultDirectlyReferencedTypeLookupOptions);
  } else if (Type type = attr->getType()) {
    return type->getAnyNominal();
  }

  // Dig out the nominal type declarations.
  SmallVector<ModuleDecl *, 2> modulesFound;
  bool anyObject = false;
  auto nominals = resolveTypeDeclsToNominal(evaluator, ctx, decls.first,
                                            ResolveToNominalOptions(),
                                            modulesFound, anyObject);
  // If we're preferring property wrappers and found a suitable match, continue.
  // Otherwise we can bail and resolve as a macro.
  if (shouldPreferPropWrapper) {
    auto hasPropWrapper = llvm::any_of(nominals, [](NominalTypeDecl *NTD) {
      return NTD->getAttrs().hasAttribute<PropertyWrapperAttr>();
    });
    if (!macros.empty() && !hasPropWrapper)
      return nullptr;
  }
  if (nominals.size() == 1 && !isa<ProtocolDecl>(nominals.front()))
    return nominals.front();

  // If we found declarations that are associated types, look outside of
  // the current context to see if we can recover.
  if (declsAreAssociatedTypes(decls.first)) {
    if (auto *unqualIdentRepr =
            dyn_cast_or_null<UnqualifiedIdentTypeRepr>(attr->getTypeRepr())) {
      if (!unqualIdentRepr->hasGenericArgList()) {
        auto assocType = cast<AssociatedTypeDecl>(decls.first.front());

        const auto name = unqualIdentRepr->getNameRef();
        const auto nameLoc = unqualIdentRepr->getNameLoc();
        const auto loc = unqualIdentRepr->getLoc();

        modulesFound.clear();
        anyObject = false;
        decls = directReferencesForUnqualifiedTypeLookup(
            name, loc, dc, LookupOuterResults::Included,
            defaultDirectlyReferencedTypeLookupOptions);
        nominals = resolveTypeDeclsToNominal(evaluator, ctx, decls.first,
                                             ResolveToNominalOptions(),
                                             modulesFound, anyObject);
        if (nominals.size() == 1 && !isa<ProtocolDecl>(nominals.front())) {
          auto nominal = nominals.front();
          if (nominal->getDeclContext()->isModuleScopeContext()) {
            // Complain, producing module qualification in a Fix-It.
            auto moduleName = nominal->getParentModule()->getName();
            ctx.Diags
                .diagnose(loc, diag::warn_property_wrapper_module_scope, name,
                          moduleName)
                .fixItInsert(loc, moduleName.str().str() + ".");
            ctx.Diags.diagnose(assocType, diag::decl_declared_here_with_kind,
                               assocType);

            auto *baseTR = UnqualifiedIdentTypeRepr::create(
                ctx, nameLoc, DeclNameRef(moduleName));

            auto *newTE = new (ctx) TypeExpr(
                QualifiedIdentTypeRepr::create(ctx, baseTR, nameLoc, name));
            attr->resetTypeInformation(newTE);
            return nominal;
          }
        }
      }
    }
  }

  return nullptr;
}

/// Decompose the ith inheritance clause entry to a list of type declarations,
/// inverses, and optional AnyObject member.
void swift::getDirectlyInheritedNominalTypeDecls(
    llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
    unsigned i, llvm::SmallVectorImpl<InheritedNominalEntry> &result,
    InvertibleProtocolSet &inverses, bool &anyObject) {
  auto typeDecl = decl.dyn_cast<const TypeDecl *>();
  auto extDecl = decl.dyn_cast<const ExtensionDecl *>();

  ASTContext &ctx = typeDecl ? typeDecl->getASTContext()
                             : extDecl->getASTContext();

  // Find inherited declarations.
  auto referenced = evaluateOrDefault(ctx.evaluator,
    InheritedDeclsReferencedRequest{decl, i}, {});

  // Apply inverses written on this inheritance clause entry.
  inverses.insertAll(referenced.second);

  // Resolve those type declarations to nominal type declarations.
  SmallVector<ModuleDecl *, 2> modulesFound;
  auto nominalTypes
    = resolveTypeDeclsToNominal(ctx.evaluator, ctx, referenced.first,
                                ResolveToNominalOptions(),
                                modulesFound, anyObject);

  // Dig out the source location
  // FIXME: This is a hack. We need cooperation from
  // InheritedDeclsReferencedRequest to make this work.
  SourceLoc loc;
  ConformanceAttributes attributes;
  auto inheritedTypes = InheritedTypes(decl);
  bool isSuppressed = inheritedTypes.getEntry(i).isSuppressed();
  if (TypeRepr *typeRepr = inheritedTypes.getTypeRepr(i)) {
    loc = typeRepr->getLoc();
    attributes.uncheckedLoc = typeRepr->findAttrLoc(TypeAttrKind::Unchecked);
    attributes.preconcurrencyLoc = typeRepr->findAttrLoc(TypeAttrKind::Preconcurrency);
    attributes.unsafeLoc = typeRepr->findAttrLoc(TypeAttrKind::Unsafe);
    attributes.nonisolatedLoc = typeRepr->findAttrLoc(TypeAttrKind::Nonisolated);

    // Dig out the custom attribute that should be the global actor isolation.
    if (auto customAttr = typeRepr->findCustomAttr()) {
      if (!customAttr->hasArgs()) {
        if (auto customAttrTypeExpr = customAttr->getTypeExpr()) {
          attributes.globalActorAtLoc = customAttr->AtLoc;
          attributes.globalActorType = customAttrTypeExpr;
        }
      }
    }
  }

  // Form the result.
  for (auto nominal : nominalTypes) {
    result.push_back({nominal, loc, inheritedTypes.getTypeRepr(i), attributes,
                      isSuppressed});
  }
}

/// Decompose all inheritance clause entries and return the union of their
/// type declarations, inverses, and optional AnyObject member.
SmallVector<InheritedNominalEntry, 4>
swift::getDirectlyInheritedNominalTypeDecls(
    llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
    InvertibleProtocolSet &inverses, bool &anyObject) {
  SmallVector<InheritedNominalEntry, 4> result;

  auto inheritedTypes = InheritedTypes(decl);
  for (unsigned i : inheritedTypes.getIndices()) {
    getDirectlyInheritedNominalTypeDecls(decl, i, result, inverses, anyObject);
  }

  auto *typeDecl = decl.dyn_cast<const TypeDecl *>();
  auto *protoDecl = dyn_cast_or_null<ProtocolDecl>(typeDecl);
  if (!protoDecl)
    return result;

  assert(!protoDecl->wasDeserialized() && "Use getInheritedProtocols()");

  // Check for SynthesizedProtocolAttrs on the protocol. ClangImporter uses
  // these to add `Sendable` conformances to protocols without modifying the
  // inherited type list.
  for (auto attr :
       protoDecl->getAttrs().getAttributes<SynthesizedProtocolAttr>()) {
    auto loc = attr->getLocation();
    ConformanceAttributes attributes;
    if (attr->isUnchecked())
      attributes.uncheckedLoc = loc;
    result.push_back({attr->getProtocol(), loc, /*inheritedTypeRepr=*/nullptr,
                      attributes, attr->isSuppressed()});
  }

  // Else we have access to this information on the where clause.
  auto selfBounds = getSelfBoundsFromWhereClause(decl);
  inverses.insertAll(selfBounds.inverses);
  anyObject |= selfBounds.anyObject;

  // FIXME: Refactor SelfBoundsFromWhereClauseRequest to dig out
  // the source location.
  for (auto inheritedNominal : selfBounds.decls)
    result.emplace_back(inheritedNominal, SourceLoc(),
                        /*inheritedTypeRepr=*/nullptr, ConformanceAttributes(),
                        /*isSuppressed=*/false);

  return result;
}

bool IsCallAsFunctionNominalRequest::evaluate(Evaluator &evaluator,
                                              NominalTypeDecl *decl,
                                              DeclContext *dc) const {
  auto &ctx = dc->getASTContext();

  // Do a qualified lookup for `callAsFunction`. We want to ignore access, as
  // that will be checked when we actually try to solve with a `callAsFunction`
  // member access.
  SmallVector<ValueDecl *, 4> results;
  auto opts = NL_QualifiedDefault | NL_ProtocolMembers |
              NL_IgnoreAccessControl | NL_IgnoreMissingImports;
  dc->lookupQualified(decl, DeclNameRef(ctx.Id_callAsFunction),
                      decl->getLoc(), opts, results);

  return llvm::any_of(results, [](ValueDecl *decl) -> bool {
    if (auto *fd = dyn_cast<FuncDecl>(decl))
      return fd->isCallAsFunctionMethod();
    return false;
  });
}

bool TypeBase::isCallAsFunctionType(DeclContext *dc) {
  // We can perform the lookup at module scope to allow us to better cache the
  // result across different contexts. Given we'll be doing a qualified lookup,
  // this shouldn't make a difference.
  dc = dc->getModuleScopeContext();

  // Note this excludes AnyObject.
  SmallVector<NominalTypeDecl *, 4> decls;
  tryExtractDirectlyReferencedNominalTypes(this, decls);

  auto &ctx = dc->getASTContext();
  return llvm::any_of(decls, [&](auto *decl) {
    IsCallAsFunctionNominalRequest req(decl, dc);
    return evaluateOrDefault(ctx.evaluator, req, false);
  });
}

template <class DynamicAttribute, class Req>
static bool checkForDynamicAttribute(Evaluator &eval, NominalTypeDecl *decl) {
  // If this type has the attribute on it, then yes!
  if (decl->getAttrs().hasAttribute<DynamicAttribute>())
    return true;

  auto hasAttribute = [&](NominalTypeDecl *decl) -> bool {
    return evaluateOrDefault(eval, Req{decl}, false);
  };

  if (auto *proto = dyn_cast<ProtocolDecl>(decl)) {
    // Check inherited protocols of a protocol.
    for (auto *otherProto : proto->getInheritedProtocols())
      if (hasAttribute(otherProto))
        return true;
  } else {
    // Check the protocols the type conforms to.
    for (auto *otherProto : decl->getAllProtocols()) {
      if (hasAttribute(otherProto))
        return true;
    }
  }

  // Check the superclass if present.
  if (auto *classDecl = dyn_cast<ClassDecl>(decl)) {
    if (auto *superclass = classDecl->getSuperclassDecl()) {
      if (hasAttribute(superclass))
        return true;
    }
  }
  return false;
}

bool HasDynamicMemberLookupAttributeRequest::evaluate(
    Evaluator &eval, NominalTypeDecl *decl) const {
  using Req = HasDynamicMemberLookupAttributeRequest;
  return checkForDynamicAttribute<DynamicMemberLookupAttr, Req>(eval, decl);
}

bool TypeBase::hasDynamicMemberLookupAttribute() {
  SmallVector<NominalTypeDecl *, 4> decls;
  tryExtractDirectlyReferencedNominalTypes(this, decls);

  auto &ctx = getASTContext();
  return llvm::any_of(decls, [&](auto *decl) {
    HasDynamicMemberLookupAttributeRequest req(decl);
    return evaluateOrDefault(ctx.evaluator, req, false);
  });
}

bool HasDynamicCallableAttributeRequest::evaluate(Evaluator &eval,
                                                  NominalTypeDecl *decl) const {
  using Req = HasDynamicCallableAttributeRequest;
  return checkForDynamicAttribute<DynamicCallableAttr, Req>(eval, decl);
}

bool TypeBase::hasDynamicCallableAttribute() {
  SmallVector<NominalTypeDecl *, 4> decls;
  tryExtractDirectlyReferencedNominalTypes(this, decls);

  auto &ctx = getASTContext();
  return llvm::any_of(decls, [&](auto *decl) {
    HasDynamicCallableAttributeRequest req(decl);
    return evaluateOrDefault(ctx.evaluator, req, false);
  });
}

ProtocolDecl *ImplementsAttrProtocolRequest::evaluate(
    Evaluator &evaluator, const ImplementsAttr *attr, DeclContext *dc) const {

  auto typeRepr = attr->getProtocolTypeRepr();

  ASTContext &ctx = dc->getASTContext();
  DirectlyReferencedTypeDecls referenced = directReferencesForTypeRepr(
      evaluator, ctx, typeRepr, dc, defaultDirectlyReferencedTypeLookupOptions);

  // Resolve those type declarations to nominal type declarations.
  SmallVector<ModuleDecl *, 2> modulesFound;
  bool anyObject = false;
  auto nominalTypes
    = resolveTypeDeclsToNominal(evaluator, ctx, referenced.first,
                                ResolveToNominalOptions(),
                                modulesFound, anyObject);

  if (nominalTypes.empty())
    return nullptr;

  return dyn_cast<ProtocolDecl>(nominalTypes.front());
}

FuncDecl *LookupIntrinsicRequest::evaluate(Evaluator &evaluator,
                                           ModuleDecl *module,
                                           Identifier funcName) const {
  llvm::SmallVector<ValueDecl *, 1> decls;
  module->lookupQualified(module, DeclNameRef(funcName), SourceLoc(),
                          NL_QualifiedDefault | NL_IncludeUsableFromInline,
                          decls);
  if (decls.size() != 1)
    return nullptr;

  return dyn_cast<FuncDecl>(decls[0]);
}

void swift::simple_display(llvm::raw_ostream &out, NLKind kind) {
  switch (kind) {
  case NLKind::QualifiedLookup:
    out << "QualifiedLookup";
    return;
  case NLKind::UnqualifiedLookup:
    out << "UnqualifiedLookup";
    return;
  }
  llvm_unreachable("Unhandled case in switch");
}

void swift::simple_display(llvm::raw_ostream &out, NLOptions options) {
  using Flag = std::pair<NLOptions, StringRef>;
  Flag possibleFlags[] = {
#define FLAG(Name) {Name, #Name},
    FLAG(NL_ProtocolMembers)
    FLAG(NL_RemoveNonVisible)
    FLAG(NL_RemoveOverridden)
    FLAG(NL_IgnoreAccessControl)
    FLAG(NL_OnlyTypes)
    FLAG(NL_IncludeAttributeImplements)
    FLAG(NL_IncludeUsableFromInline)
    FLAG(NL_ExcludeMacroExpansions)
    FLAG(NL_OnlyMacros)
    FLAG(NL_IgnoreMissingImports)
    FLAG(NL_ABIProviding)
#undef FLAG
  };

  auto flagsToPrint = llvm::make_filter_range(
      possibleFlags, [&](Flag flag) { return options & flag.first; });

  out << "{ ";
  interleave(
      flagsToPrint, [&](Flag flag) { out << flag.second; },
      [&] { out << ", "; });
  out << " }";
}