swift-mirror/lib/Sema/CSDiagnostics.cpp

//===--- CSDiagnostics.cpp - Constraint Diagnostics -----------------------===//
//
// 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 diagnostics for constraint system.
//
//===----------------------------------------------------------------------===//

#include "CSDiagnostics.h"
#include "ConstraintSystem.h"
#include "MiscDiagnostics.h"
#include "swift/AST/Expr.h"
#include "swift/AST/GenericSignature.h"
#include "swift/AST/Types.h"
#include "llvm/ADT/ArrayRef.h"

using namespace swift;
using namespace constraints;

FailureDiagnostic::~FailureDiagnostic() {}

std::pair<Expr *, bool> FailureDiagnostic::computeAnchor() const {
  auto &cs = getConstraintSystem();

  auto *locator = getLocator();
  // Resolve the locator to a specific expression.
  SourceRange range;
  bool isSubscriptMember =
      (!locator->getPath().empty() && locator->getPath().back().getKind() ==
                                          ConstraintLocator::SubscriptMember);

  ConstraintLocator *resolved = simplifyLocator(cs, locator, range);
  if (!resolved || !resolved->getAnchor())
    return {locator->getAnchor(), true};

  Expr *anchor = resolved->getAnchor();
  // FIXME: Work around an odd locator representation that doesn't separate the
  // base of a subscript member from the member access.
  if (isSubscriptMember) {
    if (auto subscript = dyn_cast<SubscriptExpr>(anchor))
      anchor = subscript->getBase();
  }

  return {anchor, !resolved->getPath().empty()};
}

Type FailureDiagnostic::getType(Expr *expr) const {
  auto &cs = getConstraintSystem();
  return solution.simplifyType(cs.getType(expr));
}

template <typename... ArgTypes>
InFlightDiagnostic
FailureDiagnostic::emitDiagnostic(ArgTypes &&... Args) const {
  auto &cs = getConstraintSystem();
  return cs.TC.diagnose(std::forward<ArgTypes>(Args)...);
}

Type RequirementFailure::getOwnerType() const {
  return getType(getAnchor())->getInOutObjectType()->getMetatypeInstanceType();
}

const Requirement &RequirementFailure::getRequirement() const {
  auto *genericCtx = AffectedDecl->getAsGenericContext();
  return genericCtx->getGenericRequirements()[getRequirementIndex()];
}

ValueDecl *RequirementFailure::getDeclRef() const {
  auto &cs = getConstraintSystem();

  auto *anchor = getAnchor();
  auto *locator = cs.getConstraintLocator(anchor);
  if (auto *AE = dyn_cast<CallExpr>(anchor)) {
    assert(isa<TypeExpr>(AE->getFn()));
    ConstraintLocatorBuilder ctor(locator);
    locator = cs.getConstraintLocator(
        ctor.withPathElement(PathEltKind::ApplyFunction)
            .withPathElement(PathEltKind::ConstructorMember));
  } else if (auto *UDE = dyn_cast<UnresolvedDotExpr>(anchor)) {
    ConstraintLocatorBuilder member(locator);
    locator =
        cs.getConstraintLocator(member.withPathElement(PathEltKind::Member));
  }

  auto overload = getOverloadChoiceIfAvailable(locator);
  if (overload)
    return overload->choice.getDecl();

  auto ownerType = getOwnerType();
  if (auto *NA = dyn_cast<NameAliasType>(ownerType.getPointer()))
    return NA->getDecl();

  return ownerType->getAnyGeneric();
}

const DeclContext *RequirementFailure::getRequirementDC() const {
  const auto &req = getRequirement();
  auto *DC = AffectedDecl->getDeclContext();

  do {
    auto *D = DC->getInnermostDeclarationDeclContext();
    if (!D)
      break;

    if (auto *GC = D->getAsGenericContext()) {
      auto *sig = GC->getGenericSignature();
      if (sig && sig->isRequirementSatisfied(req))
        return DC;
    }

    DC = DC->getParent();
  } while (DC);

  return AffectedDecl->getAsGenericContext();
}

bool MissingConformanceFailure::diagnose() {
  auto *anchor = getAnchor();
  auto ownerType = getOwnerType();
  auto type = getNonConformingType();
  auto protocolType = getProtocolType();

  //  Find `ApplyExpr` based on a function expression attached to it.
  auto findApplyExpr = [](Expr *parent, Expr *fnExpr) -> ApplyExpr * {
    ApplyExpr *applyExpr = nullptr;
    parent->forEachChildExpr([&applyExpr, &fnExpr](Expr *subExpr) -> Expr * {
      auto *AE = dyn_cast<ApplyExpr>(subExpr);
      if (!AE || AE->getFn() != fnExpr)
        return subExpr;

      applyExpr = AE;
      return nullptr;
    });
    return applyExpr;
  };

  auto getArgumentAt = [](ApplyExpr *AE, unsigned index) -> Expr * {
    assert(AE);

    auto *arg = AE->getArg();
    if (auto *TE = dyn_cast<TupleExpr>(arg))
      return TE->getElement(index);

    assert(index == 0);
    if (auto *PE = dyn_cast<ParenExpr>(arg))
      return PE->getSubExpr();

    return arg;
  };

  auto *applyExpr = findApplyExpr(getParentExpr(), anchor);

  Optional<unsigned> atParameterPos;
  // Sometimes fix is recorded by type-checking sub-expression
  // during normal diagnostics, in such case call expression
  // is unavailable.
  if (applyExpr) {
    // If this is a static, initializer or operator call,
    // let's not try to diagnose it here, but refer to expression
    // diagnostics.
    if (isa<PrefixUnaryExpr>(applyExpr) || isa<PostfixUnaryExpr>(applyExpr) ||
        isa<BinaryExpr>(applyExpr) || isa<TypeExpr>(anchor))
      return false;

    if (auto *fnType = ownerType->getAs<AnyFunctionType>()) {
      auto parameters = fnType->getParams();
      for (auto index : indices(parameters)) {
        if (parameters[index].getType()->isEqual(type)) {
          atParameterPos = index;
          break;
        }
      }
    }
  }

  if (type->isExistentialType()) {
    auto diagnostic = diag::protocol_does_not_conform_objc;
    if (type->isObjCExistentialType())
      diagnostic = diag::protocol_does_not_conform_static;

    emitDiagnostic(anchor->getLoc(), diagnostic, type, protocolType);
  } else if (atParameterPos) {
    // Requirement comes from one of the parameter types,
    // let's try to point diagnostic to the argument expression.
    auto *argExpr = getArgumentAt(applyExpr, *atParameterPos);
    emitDiagnostic(argExpr->getLoc(),
                   diag::cannot_convert_argument_value_protocol, type,
                   protocolType);
  } else {
    const auto &req = getRequirement();
    auto *genericCtx = AffectedDecl->getAsGenericContext();
    const auto *reqDC = getRequirementDC();

    if (reqDC != genericCtx) {
      auto *NTD = reqDC->getAsNominalTypeOrNominalTypeExtensionContext();
      emitDiagnostic(anchor->getLoc(), diag::type_does_not_conform_in_decl_ref,
                     AffectedDecl->getDescriptiveKind(),
                     AffectedDecl->getFullName(), NTD->getDeclaredType(), type,
                     protocolType);
    } else {
      emitDiagnostic(anchor->getLoc(), diag::type_does_not_conform_decl_owner,
                     AffectedDecl->getDescriptiveKind(),
                     AffectedDecl->getFullName(), type, protocolType);
    }

    emitDiagnostic(reqDC->getAsDeclOrDeclExtensionContext(),
                   diag::where_type_does_not_conform_type, req.getFirstType(),
                   type);
  }
  return true;
}

bool LabelingFailure::diagnose() {
  auto &cs = getConstraintSystem();
  auto *call = cast<CallExpr>(getAnchor());
  return diagnoseArgumentLabelError(cs.getASTContext(), call->getArg(),
                                    CorrectLabels,
                                    isa<SubscriptExpr>(call->getFn()));
}

bool NoEscapeFuncToTypeConversionFailure::diagnose() {
  auto *anchor = getAnchor();

  if (ConvertTo) {
    emitDiagnostic(anchor->getLoc(), diag::converting_noescape_to_type,
                   ConvertTo);
    return true;
  }

  auto path = getLocator()->getPath();
  if (path.empty())
    return false;

  auto &last = path.back();
  if (last.getKind() != ConstraintLocator::Archetype)
    return false;

  auto *archetype = last.getArchetype();
  emitDiagnostic(anchor->getLoc(), diag::converting_noescape_to_type,
                 archetype);
  return true;
}

bool MissingForcedDowncastFailure::diagnose() {
  if (hasComplexLocator())
    return false;

  auto &TC = getTypeChecker();

  auto *coerceExpr = dyn_cast<CoerceExpr>(getAnchor());
  if (!coerceExpr)
    return false;

  auto *subExpr = coerceExpr->getSubExpr();
  auto fromType = getType(subExpr)->getRValueType();
  auto toType = resolveType(coerceExpr->getCastTypeLoc().getType());

  auto castKind =
      TC.typeCheckCheckedCast(fromType, toType, CheckedCastContextKind::None,
                              getDC(), coerceExpr->getLoc(), subExpr,
                              coerceExpr->getCastTypeLoc().getSourceRange());

  switch (castKind) {
  // Invalid cast.
  case CheckedCastKind::Unresolved:
    // Fix didn't work, let diagnoseFailureForExpr handle this.
    return false;
  case CheckedCastKind::Coercion:
  case CheckedCastKind::BridgingCoercion:
    llvm_unreachable("Coercions handled in other disjunction branch");

  // Valid casts.
  case CheckedCastKind::ArrayDowncast:
  case CheckedCastKind::DictionaryDowncast:
  case CheckedCastKind::SetDowncast:
  case CheckedCastKind::ValueCast:
    emitDiagnostic(coerceExpr->getLoc(), diag::missing_forced_downcast,
                   fromType, toType)
        .highlight(coerceExpr->getSourceRange())
        .fixItReplace(coerceExpr->getLoc(), "as!");
    return true;
  }
}

bool MissingAddressOfFailure::diagnose() {
  if (hasComplexLocator())
    return false;

  auto *anchor = getAnchor();
  auto type = getType(anchor)->getRValueType();
  emitDiagnostic(anchor->getLoc(), diag::missing_address_of, type)
      .fixItInsert(anchor->getStartLoc(), "&");
  return true;
}

bool MissingExplicitConversionFailure::diagnose() {
  if (hasComplexLocator())
    return false;

  auto *DC = getDC();
  auto &TC = getTypeChecker();

  auto *anchor = getAnchor();
  if (auto *paren = dyn_cast<ParenExpr>(anchor))
    anchor = paren->getSubExpr();

  auto fromType = getType(anchor)->getRValueType();
  Type toType = resolveType(ConvertingTo);
  bool useAs = TC.isExplicitlyConvertibleTo(fromType, toType, DC);
  bool useAsBang = !useAs && TC.checkedCastMaySucceed(fromType, toType, DC);
  if (!useAs && !useAsBang)
    return false;

  auto *expr = getParentExpr();
  // If we're performing pattern matching,
  // "as" means something completely different...
  if (auto binOpExpr = dyn_cast<BinaryExpr>(expr)) {
    auto overloadedFn = dyn_cast<OverloadedDeclRefExpr>(binOpExpr->getFn());
    if (overloadedFn && !overloadedFn->getDecls().empty()) {
      ValueDecl *decl0 = overloadedFn->getDecls()[0];
      if (decl0->getBaseName() == decl0->getASTContext().Id_MatchOperator)
        return false;
    }
  }

  bool needsParensInside = exprNeedsParensBeforeAddingAs(anchor);
  bool needsParensOutside = exprNeedsParensAfterAddingAs(anchor, expr);

  llvm::SmallString<2> insertBefore;
  llvm::SmallString<32> insertAfter;
  if (needsParensOutside) {
    insertBefore += "(";
  }
  if (needsParensInside) {
    insertBefore += "(";
    insertAfter += ")";
  }
  insertAfter += useAs ? " as " : " as! ";
  insertAfter += toType->getWithoutParens()->getString();
  if (needsParensOutside)
    insertAfter += ")";

  auto diagID =
      useAs ? diag::missing_explicit_conversion : diag::missing_forced_downcast;
  auto diag = emitDiagnostic(anchor->getLoc(), diagID, fromType, toType);
  if (!insertBefore.empty()) {
    diag.fixItInsert(anchor->getStartLoc(), insertBefore);
  }
  diag.fixItInsertAfter(anchor->getEndLoc(), insertAfter);
  return true;
}

bool MemberAccessOnOptionalBaseFailure::diagnose() {
  if (hasComplexLocator())
    return false;

  auto *anchor = getAnchor();
  auto type = getType(anchor)->getRValueType();
  bool resultIsOptional = ResultTypeIsOptional;

  // If we've resolved the member overload to one that returns an optional
  // type, then the result of the expression is optional (and we want to offer
  // only a '?' fixit) even though the constraint system didn't need to add any
  // additional optionality.
  auto overload = getResolvedOverload(getLocator());
  if (overload && overload->ImpliedType->getOptionalObjectType())
    resultIsOptional = true;

  return diagnoseBaseUnwrapForMemberAccess(anchor, type, Member,
                                           resultIsOptional, SourceRange());
}

// Suggest a default value via ?? <default value>
static void offerDefaultValueUnwrapFixit(TypeChecker &TC, DeclContext *DC, Expr *expr) {
  auto diag =
  TC.diagnose(expr->getLoc(), diag::unwrap_with_default_value);

  // Figure out what we need to parenthesize.
  bool needsParensInside =
  exprNeedsParensBeforeAddingNilCoalescing(TC, DC, expr);
  bool needsParensOutside =
  exprNeedsParensAfterAddingNilCoalescing(TC, DC, expr, expr);

  llvm::SmallString<2> insertBefore;
  llvm::SmallString<32> insertAfter;
  if (needsParensOutside) {
    insertBefore += "(";
  }
  if (needsParensInside) {
    insertBefore += "(";
    insertAfter += ")";
  }
  insertAfter += " ?? <" "#default value#" ">";
  if (needsParensOutside)
    insertAfter += ")";

  if (!insertBefore.empty()) {
    diag.fixItInsert(expr->getStartLoc(), insertBefore);
  }
  diag.fixItInsertAfter(expr->getEndLoc(), insertAfter);
}

// Suggest a force-unwrap.
static void offerForceUnwrapFixit(ConstraintSystem &CS, Expr *expr) {
  auto diag = CS.TC.diagnose(expr->getLoc(), diag::unwrap_with_force_value);

  // If expr is optional as the result of an optional chain and this last
  // dot isn't a member returning optional, then offer to force the last
  // link in the chain, rather than an ugly parenthesized postfix force.
  if (auto optionalChain = dyn_cast<OptionalEvaluationExpr>(expr)) {
    if (auto dotExpr =
        dyn_cast<UnresolvedDotExpr>(optionalChain->getSubExpr())) {
      auto bind = dyn_cast<BindOptionalExpr>(dotExpr->getBase());
      if (bind && !CS.getType(dotExpr)->getOptionalObjectType()) {
        diag.fixItReplace(SourceRange(bind->getLoc()), "!");
        return;
      }
    }
  }

  if (expr->canAppendPostfixExpression(true)) {
    diag.fixItInsertAfter(expr->getEndLoc(), "!");
  } else {
    diag.fixItInsert(expr->getStartLoc(), "(")
    .fixItInsertAfter(expr->getEndLoc(), ")!");
  }
}

class VarDeclMultipleReferencesChecker : public ASTWalker {
  VarDecl *varDecl;
  int count;

  std::pair<bool, Expr *> walkToExprPre(Expr *E) {
    if (auto *DRE = dyn_cast<DeclRefExpr>(E)) {
      if (DRE->getDecl() == varDecl)
        count++;
    }
    return { true, E };
  }

public:
  VarDeclMultipleReferencesChecker(VarDecl *varDecl) : varDecl(varDecl),count(0) {}
  int referencesCount() { return count; }
};

static bool diagnoseUnwrap(ConstraintSystem &CS, Expr *expr, Type type) {
  Type unwrappedType = type->getOptionalObjectType();
  if (!unwrappedType)
    return false;

  CS.TC.diagnose(expr->getLoc(), diag::optional_not_unwrapped, type,
                 unwrappedType);

  // If the expression we're unwrapping is the only reference to a
  // local variable whose type isn't explicit in the source, then
  // offer unwrapping fixits on the initializer as well.
  if (auto declRef = dyn_cast<DeclRefExpr>(expr)) {
    if (auto varDecl = dyn_cast<VarDecl>(declRef->getDecl())) {

      bool singleUse = false;
      AbstractFunctionDecl *AFD = nullptr;
      if (auto contextDecl = varDecl->getDeclContext()->getAsDeclOrDeclExtensionContext()) {
        if ((AFD = dyn_cast<AbstractFunctionDecl>(contextDecl))) {
          auto checker = VarDeclMultipleReferencesChecker(varDecl);
          AFD->getBody()->walk(checker);
          singleUse = checker.referencesCount() == 1;
        }
      }

      PatternBindingDecl *binding = varDecl->getParentPatternBinding();
      if (singleUse && binding && binding->getNumPatternEntries() == 1 &&
          varDecl->getTypeSourceRangeForDiagnostics().isInvalid()) {

        Expr *initializer = varDecl->getParentInitializer();
        if (auto declRefExpr = dyn_cast<DeclRefExpr>(initializer)) {
          if (declRefExpr->getDecl()->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>()) {
            CS.TC.diagnose(declRefExpr->getLoc(), diag::unwrap_iuo_initializer, type);
          }
        }

        auto fnTy = AFD->getInterfaceType()->castTo<AnyFunctionType>();
        bool voidReturn = fnTy->getResult()->isEqual(TupleType::getEmpty(CS.DC->getASTContext()));

        auto diag = CS.TC.diagnose(varDecl->getLoc(), diag::unwrap_with_guard);
        diag.fixItInsert(binding->getStartLoc(), "guard ");
        if (voidReturn) {
          diag.fixItInsertAfter(binding->getEndLoc(), " else { return }");
        } else {
          diag.fixItInsertAfter(binding->getEndLoc(), " else { return <"
                                "#default value#" "> }");
        }
        diag.flush();

        offerDefaultValueUnwrapFixit(CS.TC, varDecl->getDeclContext(),
                                     initializer);
        offerForceUnwrapFixit(CS, initializer);
      }
    }
  }

  offerDefaultValueUnwrapFixit(CS.TC, CS.DC, expr);
  offerForceUnwrapFixit(CS, expr);
  return true;
}

bool MissingOptionalUnwrapFailure::diagnose() {
  if (hasComplexLocator())
    return false;

  auto *anchor = getAnchor();
  auto *unwrapped = anchor->getValueProvidingExpr();
  auto type = getType(anchor)->getRValueType();

  auto *tryExpr = dyn_cast<OptionalTryExpr>(unwrapped);
  if (!tryExpr)
    return diagnoseUnwrap(getConstraintSystem(), unwrapped, type);

  emitDiagnostic(tryExpr->getTryLoc(), diag::missing_unwrap_optional_try, type)
      .fixItReplace({tryExpr->getTryLoc(), tryExpr->getQuestionLoc()}, "try!");
  return true;
}