//===--- SendNonSendable.cpp ----------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2024 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
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "send-non-sendable"

#include "swift/SIL/PrunedLiveness.h"

#include "swift/AST/ASTWalker.h"
#include "swift/AST/Concurrency.h"
#include "swift/AST/DiagnosticsSIL.h"
#include "swift/AST/Expr.h"
#include "swift/AST/ProtocolConformance.h"
#include "swift/AST/SourceFile.h"
#include "swift/AST/Type.h"
#include "swift/Basic/Assertions.h"
#include "swift/Basic/FrozenMultiMap.h"
#include "swift/Basic/ImmutablePointerSet.h"
#include "swift/SIL/BasicBlockData.h"
#include "swift/SIL/BasicBlockDatastructures.h"
#include "swift/SIL/DynamicCasts.h"
#include "swift/SIL/MemAccessUtils.h"
#include "swift/SIL/NodeDatastructures.h"
#include "swift/SIL/OperandDatastructures.h"
#include "swift/SIL/OwnershipUtils.h"
#include "swift/SIL/PatternMatch.h"
#include "swift/SIL/SILBasicBlock.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/SILInstruction.h"
#include "swift/SIL/Test.h"
#include "swift/SILOptimizer/Analysis/RegionAnalysis.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/PartitionUtils.h"
#include "swift/SILOptimizer/Utils/VariableNameUtils.h"
#include "swift/Sema/Concurrency.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/Debug.h"

using namespace swift;
using namespace swift::PartitionPrimitives;
using namespace swift::PatternMatch;
using namespace swift::regionanalysisimpl;

namespace {

using SendingOperandSetFactory = Partition::SendingOperandSetFactory;
using Element = PartitionPrimitives::Element;
using Region = PartitionPrimitives::Region;

} // namespace

// This option is used so we can test typed errors. Typed errors are a fallback
// case which are emitted when we are unable to infer the name of a value. We in
// most cases do succeed inferring, so it makes sense to add an asserts only
// option that can be used by the compiler to test that we emit these correctly.
static llvm::cl::opt<bool> ForceTypedErrors(
    "sil-regionbasedisolation-force-use-of-typed-errors",
    llvm::cl::desc("Force the usage of typed instead of named errors to make "
                   "it easier to test typed errors"),
    llvm::cl::Hidden);

//===----------------------------------------------------------------------===//
//                              MARK: Utilities
//===----------------------------------------------------------------------===//

static SILValue stripFunctionConversions(SILValue val) {
  while (true) {
    if (auto ti = dyn_cast<ThinToThickFunctionInst>(val)) {
      val = ti->getOperand();
      continue;
    }

    if (auto cfi = dyn_cast<ConvertFunctionInst>(val)) {
      val = cfi->getOperand();
      continue;
    }

    if (auto cvt = dyn_cast<ConvertEscapeToNoEscapeInst>(val)) {
      val = cvt->getOperand();
      continue;
    }

    // Look through thunks.
    if (auto pai = dyn_cast<PartialApplyInst>(val)) {
      if (pai->getCalleeFunction()->isThunk()) {
        val = pai->getArgument(0);
        continue;
      }
    }

    break;
  }

  return val;
}

/// Find the most conservative diagnostic behavior by taking the max over all
/// DiagnosticBehavior for the captured values.
static std::optional<DiagnosticBehavior>
getDiagnosticBehaviorLimitForOperands(SILFunction *fn,
                                      ArrayRef<Operand *> capturedValues) {
  std::optional<DiagnosticBehavior> diagnosticBehavior;
  for (auto value : capturedValues) {
    auto lhs = diagnosticBehavior.value_or(DiagnosticBehavior::Unspecified);
    auto limit = value->get()->getType().getConcurrencyDiagnosticBehavior(fn);
    auto rhs = limit.value_or(DiagnosticBehavior::Unspecified);
    auto result = lhs.merge(rhs);
    if (result != DiagnosticBehavior::Unspecified)
      diagnosticBehavior = result;
  }
  return diagnosticBehavior;
}

static std::optional<SILDeclRef> getDeclRefForCallee(SILInstruction *inst) {
  auto fas = FullApplySite::isa(inst);
  if (!fas)
    return {};

  SILValue calleeOrigin = fas.getCalleeOrigin();

  while (true) {
    // Intentionally don't lookup through dynamic_function_ref and
    // previous_dynamic_function_ref as the target of those functions is not
    // statically known.
    if (auto *fri = dyn_cast<FunctionRefInst>(calleeOrigin)) {
      if (auto *callee = fri->getReferencedFunctionOrNull()) {
        if (auto declRef = callee->getDeclRef())
          return declRef;
      }
    }

    if (auto *mi = dyn_cast<MethodInst>(calleeOrigin)) {
      return mi->getMember();
    }

    if (auto *pai = dyn_cast<PartialApplyInst>(calleeOrigin)) {
      calleeOrigin = pai->getCalleeOrigin();
      continue;
    }

    return {};
  }
}

static std::optional<ValueDecl *> getSendingApplyCallee(SILInstruction *inst) {
  auto declRef = getDeclRefForCallee(inst);
  if (!declRef)
    return {};

  auto *decl = declRef->getDecl();
  if (!decl)
    return {};

  return decl;
}

static Expr *inferArgumentExprFromApplyExpr(ApplyExpr *sourceApply,
                                            FullApplySite fai,
                                            const Operand *op) {

  Expr *foundExpr = nullptr;

  // If we have self, then infer it.
  if (fai.hasSelfArgument() && op == &fai.getSelfArgumentOperand()) {
    if (auto callExpr = dyn_cast<CallExpr>(sourceApply))
      if (auto calledExpr =
              dyn_cast<DotSyntaxCallExpr>(callExpr->getDirectCallee()))
        foundExpr = calledExpr->getBase();
  } else {
    // Otherwise, try to infer using the operand of the ApplyExpr.
    unsigned argNum = [&]() -> unsigned {
      if (fai.isCalleeOperand(*op))
        return op->getOperandNumber();
      return fai.getAppliedArgIndexWithoutIndirectResults(*op);
    }();

    // Something happened that we do not understand.
    if (argNum >= sourceApply->getArgs()->size()) {
      return nullptr;
    }

    foundExpr = sourceApply->getArgs()->getExpr(argNum);

    // If we have an erasure expression, lets use the original type. We do
    // this since we are not saying the specific parameter that is the
    // issue and we are using the type to explain it to the user.
    if (auto *erasureExpr = dyn_cast<ErasureExpr>(foundExpr))
      foundExpr = erasureExpr->getSubExpr();
  }

  return foundExpr;
}

/// Attempt to infer a name for \p value. Returns none if we fail or if we are
/// asked to force typed errors since we are testing.
static std::optional<Identifier> inferNameHelper(SILValue value) {
  if (ForceTypedErrors)
    return {};
  return VariableNameInferrer::inferName(value);
}

/// Attempt to infer a name and root for \p value. Returns none if we fail or if
/// we are asked to force typed errors since we are testing.
static std::optional<std::pair<Identifier, SILValue>>
inferNameAndRootHelper(SILValue value) {
  if (ForceTypedErrors)
    return {};
  return VariableNameInferrer::inferNameAndRoot(value);
}

/// Find a use corresponding to the potentially recursive capture of \p
/// initialOperand that would be appropriate for diagnostics.
///
/// \returns the use and the function argument that is used. We return the
/// function argument since it is a clever way to correctly grab the name of the
/// captured value since the ValueDecl will point at the actual ValueDecl in the
/// AST that is captured.
static std::optional<std::pair<Operand *, SILArgument *>>
findClosureUse(Operand *initialOperand) {
  // We have to use a small vector worklist here since we are iterating through
  // uses from different functions.
  llvm::SmallVector<std::pair<Operand *, SILArgument *>, 64> worklist;
  llvm::SmallPtrSet<Operand *, 8> visitedOperand;

  // Initialize our worklist with uses in the initial closure. We do not want to
  // analyze uses in the original function.
  {
    auto as = ApplySite::isa(initialOperand->getUser());
    if (!as)
      return {};

    auto *f = as.getCalleeFunction();
    if (!f || f->empty())
      return {};

    unsigned argumentIndex = as.getCalleeArgIndex(*initialOperand);
    auto *arg = f->getArgument(argumentIndex);
    for (auto *use : arg->getUses()) {
      worklist.emplace_back(use, arg);
      visitedOperand.insert(use);
    }
  }

  while (!worklist.empty()) {
    auto pair = worklist.pop_back_val();
    auto *op = pair.first;
    auto *fArg = pair.second;
    auto *user = op->getUser();

    // Ignore incidental uses that are not specifically ignored use. We want to
    // visit those since they represent `let _ = $VAR` and `_ = $VAR`
    if (isIncidentalUse(user) && !isa<IgnoredUseInst>(user))
      continue;

    // Look through some insts we do not care about.
    if (isa<CopyValueInst, BeginBorrowInst, ProjectBoxInst, BeginAccessInst>(
            user) ||
        isMoveOnlyWrapperUse(user) ||
        // We want to treat move_value [var_decl] as a real use since we are
        // assigning to a var.
        (isa<MoveValueInst>(user) &&
         !cast<MoveValueInst>(user)->isFromVarDecl())) {
      for (auto result : user->getResults()) {
        for (auto *use : result->getUses()) {
          if (visitedOperand.insert(use).second)
            worklist.emplace_back(use, fArg);
        }
      }
      continue;
    }

    // See if we have a callee function. In such a case, find our operand in the
    // callee and visit its uses.
    if (auto as = dyn_cast<PartialApplyInst>(op->getUser())) {
      if (auto *f = as->getCalleeFunction(); f && !f->empty()) {
        auto *fArg = f->getArgument(ApplySite(as).getCalleeArgIndex(*op));
        for (auto *use : fArg->getUses()) {
          if (visitedOperand.insert(use).second)
            worklist.emplace_back(use, fArg);
        }
        continue;
      }
    }

    // See if we have a full apply site that was from a closure that was
    // immediately invoked. In such a case, we can emit a better diagnostic in
    // the called closure.
    if (auto fas = FullApplySite::isa(op->getUser())) {
      if (auto *f = fas.getCalleeFunction(); f && !f->empty()) {
        auto *fArg = cast<SILFunctionArgument>(
            f->getArgument(fas.getCalleeArgIndex(*op)));
        if (fArg->isClosureCapture()) {
          for (auto *use : fArg->getUses()) {
            if (visitedOperand.insert(use).second)
              worklist.emplace_back(use, fArg);
          }
          continue;
        }
      }
    }

    // Otherwise, we have a real use. Return it and the function argument that
    // it was derived from.
    return pair;
  }

  return {};
}

//===----------------------------------------------------------------------===//
//                             MARK: Diagnostics
//===----------------------------------------------------------------------===//

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseError(ASTContext &context, SourceLoc loc,
                                        Diag<T...> diag, U &&...args) {
  return std::move(context.Diags.diagnose(loc, diag, std::forward<U>(args)...)
                       .warnUntilSwiftVersion(6));
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseError(ASTContext &context, SILLocation loc,
                                        Diag<T...> diag, U &&...args) {
  return ::diagnoseError(context, loc.getSourceLoc(), diag,
                         std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseError(const PartitionOp &op, Diag<T...> diag,
                                        U &&...args) {
  return ::diagnoseError(op.getSourceInst()->getFunction()->getASTContext(),
                         op.getSourceLoc().getSourceLoc(), diag,
                         std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseError(const Operand *op, Diag<T...> diag,
                                        U &&...args) {
  return ::diagnoseError(op->getUser()->getFunction()->getASTContext(),
                         op->getUser()->getLoc().getSourceLoc(), diag,
                         std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseError(const SILInstruction *inst,
                                        Diag<T...> diag, U &&...args) {
  return ::diagnoseError(inst->getFunction()->getASTContext(),
                         inst->getLoc().getSourceLoc(), diag,
                         std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseNote(ASTContext &context, SourceLoc loc,
                                       Diag<T...> diag, U &&...args) {
  return context.Diags.diagnose(loc, diag, std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseNote(ASTContext &context, SILLocation loc,
                                       Diag<T...> diag, U &&...args) {
  return ::diagnoseNote(context, loc.getSourceLoc(), diag,
                        std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseNote(const PartitionOp &op, Diag<T...> diag,
                                       U &&...args) {
  return ::diagnoseNote(op.getSourceInst()->getFunction()->getASTContext(),
                        op.getSourceLoc().getSourceLoc(), diag,
                        std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseNote(const Operand *op, Diag<T...> diag,
                                       U &&...args) {
  return ::diagnoseNote(op->getUser()->getFunction()->getASTContext(),
                        op->getUser()->getLoc().getSourceLoc(), diag,
                        std::forward<U>(args)...);
}

template <typename... T, typename... U>
static InFlightDiagnostic diagnoseNote(const SILInstruction *inst,
                                       Diag<T...> diag, U &&...args) {
  return ::diagnoseNote(inst->getFunction()->getASTContext(),
                        inst->getLoc().getSourceLoc(), diag,
                        std::forward<U>(args)...);
}

//===----------------------------------------------------------------------===//
//                           MARK: Require Liveness
//===----------------------------------------------------------------------===//

namespace {

class BlockLivenessInfo {
  // Generation counter so we do not need to reallocate.
  unsigned generation = 0;
  SILInstruction *firstRequireInst = nullptr;

  void resetIfNew(unsigned newGeneration) {
    if (generation == newGeneration)
      return;
    generation = newGeneration;
    firstRequireInst = nullptr;
  }

public:
  SILInstruction *getInst(unsigned callerGeneration) {
    resetIfNew(callerGeneration);
    return firstRequireInst;
  }

  void setInst(unsigned callerGeneration, SILInstruction *newValue) {
    resetIfNew(callerGeneration);
    firstRequireInst = newValue;
  }
};

/// We only want to emit errors for the first requires along a path from a
/// sending instruction. We discover this by walking from user blocks to
struct RequireLiveness {
  unsigned generation;
  SILInstruction *sendingInst;
  BasicBlockData<BlockLivenessInfo> &blockLivenessInfo;
  InstructionSet allRequires;
  InstructionSetWithSize finalRequires;

  /// If we have requires in the def block before our send, this is the
  /// first require.
  SILInstruction *firstRequireBeforeSendInDefBlock = nullptr;

  RequireLiveness(unsigned generation, Operand *sendingOp,
                  BasicBlockData<BlockLivenessInfo> &blockLivenessInfo)
      : generation(generation), sendingInst(sendingOp->getUser()),
        blockLivenessInfo(blockLivenessInfo),
        allRequires(sendingOp->getParentFunction()),
        finalRequires(sendingOp->getParentFunction()) {}

  template <typename Collection>
  void process(Collection collection);

  /// Attempt to process requireInst for our def block. Returns false if
  /// requireInst was before our def and we need to do interprocedural
  /// processing. Returns true if requireInst was after our seningInst and we
  /// were able to appropriately determine if we should emit it or not.
  void processDefBlock();

  /// Process all requires in block, updating blockLivenessInfo.
  void processNonDefBlock(SILBasicBlock *block);
};

} // namespace

void RequireLiveness::processDefBlock() {
  REGIONBASEDISOLATION_LOG(llvm::dbgs() << "    Processing def block!\n");
  // First walk from the beginning of the block to the send instruction to
  // see if we have any requires before our def. Once we find one, we can skip
  // the traversal and jump straight to the send.
  for (auto ii = sendingInst->getParent()->begin(),
            ie = sendingInst->getIterator();
       ii != ie; ++ii) {
    if (allRequires.contains(&*ii) && !firstRequireBeforeSendInDefBlock) {
      firstRequireBeforeSendInDefBlock = &*ii;
      REGIONBASEDISOLATION_LOG(llvm::dbgs()
                               << "        Found send before def: "
                               << *firstRequireBeforeSendInDefBlock);
      break;
    }
  }

  // Then walk from our sendingInst to the end of the block looking for the
  // first require inst. Once we find it... return.
  //
  // NOTE: We start walking at the sendingInst since the sendingInst could use
  // the requireInst as well.
  for (auto ii = sendingInst->getIterator(),
            ie = sendingInst->getParent()->end();
       ii != ie; ++ii) {
    if (!allRequires.contains(&*ii))
      continue;

    finalRequires.insert(&*ii);
    REGIONBASEDISOLATION_LOG(llvm::dbgs()
                             << "        Found send after def: " << *ii);
    return;
  }
}

void RequireLiveness::processNonDefBlock(SILBasicBlock *block) {
  // Walk from the bottom to the top... assigning to our block state.
  auto blockState = blockLivenessInfo.get(block);
  for (auto &inst : llvm::make_range(block->rbegin(), block->rend())) {
    if (!finalRequires.contains(&inst))
      continue;
    blockState.get()->setInst(generation, &inst);
  }
}

template <typename Collection>
void RequireLiveness::process(Collection requireInstList) {
  REGIONBASEDISOLATION_LOG(
      llvm::dbgs() << "==> Performing Require Liveness for: " << *sendingInst);

  // Then put all of our requires into our allRequires set.
  BasicBlockWorklist initializingWorklist(sendingInst->getFunction());
  for (auto require : requireInstList) {
    REGIONBASEDISOLATION_LOG(llvm::dbgs()
                             << "        Require Inst: " << **require);
    allRequires.insert(*require);
    initializingWorklist.pushIfNotVisited(require->getParent());
  }

  // Then process our def block to see if we have any requires before and after
  // the sendingInst...
  processDefBlock();

  // If we found /any/ requries after the sendingInst, we can bail early since
  // that is guaranteed to dominate all further requires.
  if (!finalRequires.empty()) {
    REGIONBASEDISOLATION_LOG(
        llvm::dbgs()
        << "        Found send after def in def block! Exiting early!\n");
    return;
  }

  REGIONBASEDISOLATION_LOG(llvm::dbgs()
                           << "        Did not find send after def in def "
                              "block! Walking blocks!\n");

  // If we found a send in the def block before our def, add it to the block
  // state for the def.
  if (firstRequireBeforeSendInDefBlock) {
    REGIONBASEDISOLATION_LOG(
        llvm::dbgs()
        << "        Found a require before send! Adding to block state!\n");
    auto blockState = blockLivenessInfo.get(sendingInst->getParent());
    blockState.get()->setInst(generation, firstRequireBeforeSendInDefBlock);
  }

  // Then for each require block that isn't a def block send, find the
  // earliest send inst.
  while (auto *requireBlock = initializingWorklist.pop()) {
    auto blockState = blockLivenessInfo.get(requireBlock);
    for (auto &inst : *requireBlock) {
      if (!allRequires.contains(&inst))
        continue;
      REGIONBASEDISOLATION_LOG(llvm::dbgs() << "        Mapping Block bb"
                                            << requireBlock->getDebugID()
                                            << " to: " << inst);
      blockState.get()->setInst(generation, &inst);
      break;
    }
  }

  // Then walk from our def block looking for setInst blocks.
  auto *sendingBlock = sendingInst->getParent();
  BasicBlockWorklist worklist(sendingInst->getFunction());
  for (auto *succBlock : sendingBlock->getSuccessorBlocks())
    worklist.pushIfNotVisited(succBlock);

  while (auto *next = worklist.pop()) {
    // Check if we found an earliest requires... if so, add that to final
    // requires and continue. We don't want to visit successors.
    auto blockState = blockLivenessInfo.get(next);
    if (auto *inst = blockState.get()->getInst(generation)) {
      finalRequires.insert(inst);
      continue;
    }

    // Do not look at successors of the sending block.
    if (next == sendingBlock)
      continue;

    // Otherwise, we did not find a requires and need to search further
    // successors.
    for (auto *succBlock : next->getSuccessorBlocks())
      worklist.pushIfNotVisited(succBlock);
  }
}

//===----------------------------------------------------------------------===//
//            MARK: Forward Declaration Of SendNonSendableImpl
//===----------------------------------------------------------------------===//

namespace {

/// Wrapper around a SILInstruction that internally specifies whether we are
/// dealing with an inout reinitialization needed or if it is just a normal
/// use after send.
class RequireInst {
public:
  enum Kind {
    UseAfterSend,
    InOutReinitializationNeeded,
  };

private:
  llvm::PointerIntPair<SILInstruction *, 1> instAndKind;

  RequireInst(SILInstruction *inst, Kind kind) : instAndKind(inst, kind) {}

public:
  static RequireInst forUseAfterSend(SILInstruction *inst) {
    return {inst, Kind::UseAfterSend};
  }

  static RequireInst forInOutReinitializationNeeded(SILInstruction *inst) {
    return {inst, Kind::InOutReinitializationNeeded};
  }

  SILInstruction *getInst() const { return instAndKind.getPointer(); }
  Kind getKind() const { return Kind(instAndKind.getInt()); }

  SILInstruction *operator*() const { return getInst(); }
  SILInstruction *operator->() const { return getInst(); }
};

class SendNonSendableImpl {
  RegionAnalysisFunctionInfo *info;
  SmallFrozenMultiMap<Operand *, RequireInst, 8> sendingOpToRequireInstMultiMap;
  SmallVector<PartitionOpError, 8> foundVerbatimErrors;

public:
  SendNonSendableImpl(RegionAnalysisFunctionInfo *info) : info(info) {}

  void emitDiagnostics();

private:
  void runDiagnosticEvaluator();

  void emitUseAfterSendDiagnostics();
  void emitVerbatimErrors();
};

} // namespace

//===----------------------------------------------------------------------===//
//                         MARK: Diagnostic Evaluator
//===----------------------------------------------------------------------===//

namespace {

struct DiagnosticEvaluator final
    : PartitionOpEvaluatorBaseImpl<DiagnosticEvaluator> {
  RegionAnalysisFunctionInfo *info;
  SmallFrozenMultiMap<Operand *, RequireInst, 8>
      &sendingOpToRequireInstMultiMap;

  /// An error that we know how to emit verbatim without needing to preprocess.
  ///
  /// A contrasting case here is the use after send error where we need to pair
  /// sending operands to require insts.
  SmallVectorImpl<PartitionOpError> &foundVerbatimErrors;

  DiagnosticEvaluator(Partition &workingPartition,
                      RegionAnalysisFunctionInfo *info,
                      SmallFrozenMultiMap<Operand *, RequireInst, 8>
                          &sendingOpToRequireInstMultiMap,
                      SmallVectorImpl<PartitionOpError> &foundVerbatimErrors,
                      SendingOperandToStateMap &operandToStateMap)
      : PartitionOpEvaluatorBaseImpl(
            workingPartition, info->getOperandSetFactory(), operandToStateMap),
        info(info),
        sendingOpToRequireInstMultiMap(sendingOpToRequireInstMultiMap),
        foundVerbatimErrors(foundVerbatimErrors) {}

  void handleLocalUseAfterSend(LocalUseAfterSendError &&error) const {
    const auto &partitionOp = *error.op;
    REGIONBASEDISOLATION_LOG(error.print(llvm::dbgs(), info->getValueMap()));

    // Ignore this if we are erroring on a mutable base of a Sendable value and
    // if when we sent the value's region was not closure captured.
    if (error.op->getOptions().containsOnly(
            PartitionOp::Flag::RequireOfMutableBaseOfSendableValue) &&
        !operandToStateMap.get(error.sendingOp).isClosureCaptured)
      return;

    sendingOpToRequireInstMultiMap.insert(
        error.sendingOp, RequireInst::forUseAfterSend(partitionOp.getSourceInst()));
  }

  void handleInOutSendingNotInitializedAtExitError(
      InOutSendingNotInitializedAtExitError &&error) const {
    const PartitionOp &partitionOp = *error.op;
    Operand *sendingOp = error.sendingOp;

    REGIONBASEDISOLATION_LOG(error.print(llvm::dbgs(), info->getValueMap()));

    sendingOpToRequireInstMultiMap.insert(
        sendingOp, RequireInst::forInOutReinitializationNeeded(
                       partitionOp.getSourceInst()));
  }

  void handleUnknownCodePattern(UnknownCodePatternError &&error) const {
    const PartitionOp &op = *error.op;

    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(op.getSourceInst(),
                  diag::regionbasedisolation_unknown_pattern);
  }

  void handleError(PartitionOpError &&error) {
    switch (error.getKind()) {
    case PartitionOpError::LocalUseAfterSend: {
      return handleLocalUseAfterSend(
          std::move(error).getLocalUseAfterSendError());
    }
    case PartitionOpError::InOutSendingNotDisconnectedAtExit:
    case PartitionOpError::InOutSendingReturned:
    case PartitionOpError::SentNeverSendable:
    case PartitionOpError::AssignNeverSendableIntoSendingResult:
    case PartitionOpError::NonSendableIsolationCrossingResult:
      // We are going to process these later... but dump so we can see that we
      // handled an error here. The rest of the explicit handlers will dump as
      // appropriate if they want to emit an error here (some will squelch the
      // error).
      REGIONBASEDISOLATION_LOG(error.print(llvm::dbgs(), info->getValueMap()));
      foundVerbatimErrors.emplace_back(std::move(error));
      return;
    case PartitionOpError::InOutSendingNotInitializedAtExit: {
      return handleInOutSendingNotInitializedAtExitError(
          std::move(error).getInOutSendingNotInitializedAtExitError());
    }
    case PartitionOpError::UnknownCodePattern: {
      return handleUnknownCodePattern(
          std::move(error).getUnknownCodePatternError());
    }
    }
    llvm_unreachable("Covered switch isn't covered?!");
  }

  bool isActorDerived(Element element) const {
    return info->getValueMap().getIsolationRegion(element).isActorIsolated();
  }

  /// If \p element's representative is an indirect out parameter, return
  /// that parameter.
  SILValue getIndirectOutParameter(Element element) const {
    auto rep = info->getValueMap().getRepresentativeValue(element);
    if (!rep)
      return {};
    if (auto value = dyn_cast_or_null<SILFunctionArgument>(rep.maybeGetValue());
        value && value->getArgumentConvention().isIndirectOutParameter())
      return value;
    return {};
  }

  SILValue getInOutSendingParameter(Element elt) const {
    auto rep = info->getValueMap().getRepresentativeValue(elt);
    if (!rep)
      return {};
    if (auto value = dyn_cast_or_null<SILFunctionArgument>(rep.maybeGetValue());
        value && value->getArgumentConvention().isInoutConvention() &&
        value->isSending())
      return value;
    return {};
  }

  bool isTaskIsolatedDerived(Element element) const {
    return info->getValueMap().getIsolationRegion(element).isTaskIsolated();
  }

  SILIsolationInfo::Kind hasSpecialDerivation(Element element) const {
    return info->getValueMap().getIsolationRegion(element).getKind();
  }

  SILIsolationInfo getIsolationRegionInfo(Element element) const {
    return info->getValueMap().getIsolationRegion(element);
  }

  /// Only return an element if we are already tracking value and it is
  /// non-Sendable.
  ///
  /// TODO: Can we return only
  std::optional<Element> getElement(SILValue value) const {
    auto trackableValue = info->getValueMap().getTrackableValue(value);
    if (trackableValue.value.isSendable())
      return {};
    return trackableValue.value.getID();
  }

  SILValue getRepresentative(SILValue value) const {
    return info->getValueMap()
        .getTrackableValue(value)
        .value.getRepresentative()
        .maybeGetValue();
  }

  RepresentativeValue getRepresentativeValue(Element element) const {
    return info->getValueMap().getRepresentativeValue(element);
  }

  bool isClosureCaptured(Element element, Operand *op) const {
    auto value = info->getValueMap().maybeGetRepresentative(element);
    if (!value)
      return false;
    return info->isClosureCaptured(value, op);
  }
};

} // namespace

void SendNonSendableImpl::runDiagnosticEvaluator() {
  // Then for each block...
  REGIONBASEDISOLATION_LOG(llvm::dbgs() << "Walking blocks for diagnostics.\n");
  for (auto [block, blockState] : info->getRange()) {
    REGIONBASEDISOLATION_LOG(llvm::dbgs()
                             << "|--> Block bb" << block.getDebugID() << "\n");

    if (!blockState.getLiveness()) {
      REGIONBASEDISOLATION_LOG(llvm::dbgs() << "Dead block... skipping!\n");
      continue;
    }

    REGIONBASEDISOLATION_LOG(
        llvm::dbgs() << "Entry Partition: ";
        blockState.getEntryPartition().print(llvm::dbgs()));

    // Grab its entry partition and setup an evaluator for the partition that
    // has callbacks that emit diagnsotics...
    Partition workingPartition = blockState.getEntryPartition();
    DiagnosticEvaluator eval(
        workingPartition, info, sendingOpToRequireInstMultiMap,
        foundVerbatimErrors, info->getSendingOperandToStateMap());

    // And then evaluate all of our partition ops on the entry partition.
    for (auto &partitionOp : blockState.getPartitionOps()) {
      eval.apply(partitionOp);
    }

    REGIONBASEDISOLATION_LOG(llvm::dbgs() << "Exit Partition: ";
                             workingPartition.print(llvm::dbgs()));
  }

  REGIONBASEDISOLATION_LOG(llvm::dbgs()
                           << "Finished walking blocks for diagnostics.\n");

  // Now that we have found all of our sendingInsts/Requires emit errors.
  sendingOpToRequireInstMultiMap.setFrozen();
}

//===----------------------------------------------------------------------===//
//                MARK: UseAfterSend Diagnostic Inference
//===----------------------------------------------------------------------===//

namespace {

class UseAfterSendDiagnosticEmitter {
  Operand *sendingOp;
  SmallVectorImpl<RequireInst> &requireInsts;
  bool emittedErrorDiagnostic = false;

public:
  UseAfterSendDiagnosticEmitter(Operand *sendingOp,
                                SmallVectorImpl<RequireInst> &requireInsts)
      : sendingOp(sendingOp), requireInsts(requireInsts) {}

  ~UseAfterSendDiagnosticEmitter() {
    // If we were supposed to emit a diagnostic and didn't emit an unknown
    // pattern error.
    if (!emittedErrorDiagnostic)
      emitUnknownPatternError();
  }

  SILFunction *getFunction() const { return sendingOp->getFunction(); }

  std::optional<DiagnosticBehavior> getBehaviorLimit() const {
    return sendingOp->get()->getType().getConcurrencyDiagnosticBehavior(
        getFunction());
  }

  /// Attempts to retrieve and return the callee declaration.
  std::optional<const ValueDecl *> getSendingCallee() const {
    return getSendingApplyCallee(sendingOp->getUser());
  }

  void
  emitNamedIsolationCrossingError(SILLocation loc, Identifier name,
                                  SILIsolationInfo namedValuesIsolationInfo,
                                  ApplyIsolationCrossing isolationCrossing) {
    // Emit the short error.
    diagnoseError(loc, diag::regionbasedisolation_named_send_yields_race, name)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    // Then emit the note with greater context.
    auto descriptiveKindStr =
        namedValuesIsolationInfo.printForDiagnostics(getFunction());
    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCalleeIsolation());
    auto callerIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCallerIsolation());

    bool isDisconnected = namedValuesIsolationInfo.isDisconnected();
    if (auto callee = getSendingCallee()) {
      diagnoseNote(
          loc, diag::regionbasedisolation_named_info_send_yields_race_callee,
          isDisconnected, name, descriptiveKindStr, calleeIsolationStr,
          callee.value(), callerIsolationStr);
    } else {
      diagnoseNote(loc, diag::regionbasedisolation_named_info_send_yields_race,
                   isDisconnected, name, descriptiveKindStr, calleeIsolationStr,
                   callerIsolationStr);
    }
    emitRequireInstDiagnostics();
  }

  void
  emitNamedIsolationCrossingError(SILLocation loc, Identifier name,
                                  SILIsolationInfo namedValuesIsolationInfo,
                                  ApplyIsolationCrossing isolationCrossing,
                                  const ValueDecl *callee) {
    // Emit the short error.
    diagnoseError(loc, diag::regionbasedisolation_named_send_yields_race, name)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    // Then emit the note with greater context.
    auto descriptiveKindStr =
        namedValuesIsolationInfo.printForDiagnostics(getFunction());
    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCalleeIsolation());
    auto callerIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCallerIsolation());
    bool isDisconnected = namedValuesIsolationInfo.isDisconnected();

    diagnoseNote(loc,
                 diag::regionbasedisolation_named_info_send_yields_race_callee,
                 isDisconnected, name, descriptiveKindStr, calleeIsolationStr,
                 callee, callerIsolationStr);
    emitRequireInstDiagnostics();
  }

  void emitNamedAsyncLetNoIsolationCrossingError(SILLocation loc,
                                                 Identifier name) {
    // Emit the short error.
    diagnoseError(loc, diag::regionbasedisolation_named_send_yields_race, name)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    diagnoseNote(
        loc, diag::regionbasedisolation_named_nonisolated_asynclet_name, name);
    emitRequireInstDiagnostics();
  }

  void emitTypedIsolationCrossing(SILLocation loc, Type inferredType,
                                  ApplyIsolationCrossing isolationCrossing) {
    diagnoseError(loc, diag::regionbasedisolation_type_send_yields_race,
                  inferredType)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCalleeIsolation());
    auto callerIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCallerIsolation());

    if (auto callee = getSendingCallee()) {
      diagnoseNote(loc, diag::regionbasedisolation_type_use_after_send_callee,
                   inferredType, calleeIsolationStr, callee.value(),
                   callerIsolationStr);
    } else {
      diagnoseNote(loc, diag::regionbasedisolation_type_use_after_send,
                   inferredType, calleeIsolationStr, callerIsolationStr);
    }
    emitRequireInstDiagnostics();
  }

  void emitNamedUseofStronglySentValue(SILLocation loc, Identifier name) {
    // Emit the short error.
    diagnoseError(loc, diag::regionbasedisolation_named_send_yields_race, name)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    // Then emit the note with greater context.
    diagnoseNote(
        loc, diag::regionbasedisolation_named_value_used_after_explicit_sending,
        name)
        .highlight(loc.getSourceRange());

    // Finally the require points.
    emitRequireInstDiagnostics();
  }

  void emitTypedUseOfStronglySentValue(SILLocation loc, Type inferredType) {
    diagnoseError(loc, diag::regionbasedisolation_type_send_yields_race,
                  inferredType)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());
    if (auto callee = getSendingCallee()) {
      diagnoseNote(loc,
                   diag::regionbasedisolation_typed_use_after_sending_callee,
                   inferredType, callee.value());
    } else {
      diagnoseNote(loc, diag::regionbasedisolation_typed_use_after_sending,
                   inferredType);
    }
    emitRequireInstDiagnostics();
  }

  void emitNamedIsolationCrossingDueToCapture(
      SILLocation loc, Identifier name,
      SILIsolationInfo namedValuesIsolationInfo,
      ApplyIsolationCrossing isolationCrossing) {
    // Emit the short error.
    diagnoseError(loc, diag::regionbasedisolation_named_send_yields_race, name)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    auto descriptiveKindStr =
        namedValuesIsolationInfo.printForDiagnostics(getFunction());
    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCalleeIsolation());
    auto callerIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCallerIsolation());
    bool isDisconnected = namedValuesIsolationInfo.isDisconnected();
    diagnoseNote(loc,
                 diag::regionbasedisolation_named_isolated_closure_yields_race,
                 isDisconnected, descriptiveKindStr, name, calleeIsolationStr,
                 callerIsolationStr)
        .highlight(loc.getSourceRange());
    emitRequireInstDiagnostics();
  }

  void emitTypedIsolationCrossingDueToCapture(
      SILLocation loc, Type inferredType,
      ApplyIsolationCrossing isolationCrossing) {
    diagnoseError(loc, diag::regionbasedisolation_type_send_yields_race,
                  inferredType)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCalleeIsolation());
    auto callerIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCallerIsolation());

    diagnoseNote(loc,
                 diag::regionbasedisolation_type_isolated_capture_yields_race,
                 inferredType, calleeIsolationStr, callerIsolationStr);
    emitRequireInstDiagnostics();
  }

  void emitUnknownPatternError() {
    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(sendingOp->getUser(),
                  diag::regionbasedisolation_unknown_pattern)
        .limitBehaviorIf(getBehaviorLimit());
  }

private:
  ASTContext &getASTContext() const {
    return sendingOp->getFunction()->getASTContext();
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SourceLoc loc, Diag<T...> diag,
                                   U &&...args) {
    emittedErrorDiagnostic = true;
    return std::move(getASTContext()
                         .Diags.diagnose(loc, diag, std::forward<U>(args)...)
                         .warnUntilSwiftVersion(6));
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILLocation loc, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILInstruction *inst, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SourceLoc loc, Diag<T...> diag, U &&...args) {
    return getASTContext().Diags.diagnose(loc, diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILLocation loc, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILInstruction *inst, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  void emitRequireInstDiagnostics() {
    // Now actually emit the require notes.
    while (!requireInsts.empty()) {
      auto require = requireInsts.pop_back_val();
      switch (require.getKind()) {
      case RequireInst::UseAfterSend:
        diagnoseNote(*require, diag::regionbasedisolation_maybe_race)
            .highlight(require->getLoc().getSourceRange());
        continue;
      case RequireInst::InOutReinitializationNeeded:
        diagnoseNote(
            *require,
            diag::regionbasedisolation_inout_sending_must_be_reinitialized)
            .highlight(require->getLoc().getSourceRange());
        continue;
      }
      llvm_unreachable("Covered switch isn't covered?!");
    }
  }
};

class UseAfterSendDiagnosticInferrer {
  Operand *sendingOp;
  UseAfterSendDiagnosticEmitter diagnosticEmitter;
  RegionAnalysisValueMap &valueMap;
  SendingOperandToStateMap &sendingOpToStateMap;
  SILLocation baseLoc = SILLocation::invalid();
  Type baseInferredType;

  struct AutoClosureWalker;

public:
  UseAfterSendDiagnosticInferrer(Operand *sendOp,
                                 SmallVectorImpl<RequireInst> &requireInsts,
                                 RegionAnalysisValueMap &valueMap,
                                 SendingOperandToStateMap &sendingOpToStateMap)
      : sendingOp(sendOp), diagnosticEmitter(sendOp, requireInsts),
        valueMap(valueMap), sendingOpToStateMap(sendingOpToStateMap),
        baseLoc(sendOp->getUser()->getLoc()),
        baseInferredType(sendOp->get()->getType().getASTType()) {}
  void infer();

  Operand *getSendingOperand() const { return sendingOp; }

private:
  bool initForIsolatedPartialApply(Operand *op, AbstractClosureExpr *ace);

  void initForApply(Operand *op, ApplyExpr *expr);
  void initForAutoclosure(Operand *op, AutoClosureExpr *expr);
};

} // namespace

bool UseAfterSendDiagnosticInferrer::initForIsolatedPartialApply(
    Operand *op, AbstractClosureExpr *ace) {
  auto diagnosticPair = findClosureUse(op);
  if (!diagnosticPair) {
    return false;
  }

  auto *diagnosticOp = diagnosticPair->first;

  ApplyIsolationCrossing crossing(
      *op->getFunction()->getActorIsolation(),
      *diagnosticOp->getFunction()->getActorIsolation());

  auto &state = sendingOpToStateMap.get(sendingOp);
  if (auto rootValueAndName = inferNameAndRootHelper(sendingOp->get())) {
    diagnosticEmitter.emitNamedIsolationCrossingDueToCapture(
        diagnosticOp->getUser()->getLoc(), rootValueAndName->first,
        state.isolationInfo.getIsolationInfo(), crossing);
    return true;
  }

  diagnosticEmitter.emitTypedIsolationCrossingDueToCapture(
      diagnosticOp->getUser()->getLoc(), baseInferredType, crossing);
  return true;
}

void UseAfterSendDiagnosticInferrer::initForApply(Operand *op,
                                                  ApplyExpr *sourceApply) {
  auto isolationCrossing = sourceApply->getIsolationCrossing().value();

  // Grab out full apply site and see if we can find a better expr.
  SILInstruction *i = const_cast<SILInstruction *>(op->getUser());
  auto fai = FullApplySite::isa(i);

  assert(!fai.getArgumentConvention(*op).isIndirectOutParameter() &&
         "An indirect out parameter is never sent");
  auto *foundExpr = inferArgumentExprFromApplyExpr(sourceApply, fai, op);

  auto inferredArgType =
      foundExpr ? foundExpr->findOriginalType() : baseInferredType;
  diagnosticEmitter.emitTypedIsolationCrossing(baseLoc, inferredArgType,
                                               isolationCrossing);
}

/// This walker visits an AutoClosureExpr and looks for uses of a specific
/// captured value. We want to error on the uses in the autoclosure.
struct UseAfterSendDiagnosticInferrer::AutoClosureWalker : ASTWalker {
  UseAfterSendDiagnosticInferrer &foundTypeInfo;
  ValueDecl *targetDecl;
  SILIsolationInfo targetDeclIsolationInfo;
  SmallPtrSet<Expr *, 8> visitedCallExprDeclRefExprs;

  AutoClosureWalker(UseAfterSendDiagnosticInferrer &foundTypeInfo,
                    ValueDecl *targetDecl,
                    SILIsolationInfo targetDeclIsolationInfo)
      : foundTypeInfo(foundTypeInfo), targetDecl(targetDecl),
        targetDeclIsolationInfo(targetDeclIsolationInfo) {}

  Expr *lookThroughArgExpr(Expr *expr) {
    while (true) {
      if (auto *memberRefExpr = dyn_cast<MemberRefExpr>(expr)) {
        expr = memberRefExpr->getBase();
        continue;
      }

      if (auto *cvt = dyn_cast<ImplicitConversionExpr>(expr)) {
        expr = cvt->getSubExpr();
        continue;
      }

      if (auto *e = dyn_cast<ForceValueExpr>(expr)) {
        expr = e->getSubExpr();
        continue;
      }

      if (auto *t = dyn_cast<TupleElementExpr>(expr)) {
        expr = t->getBase();
        continue;
      }

      return expr;
    }
  }

  PreWalkResult<Expr *> walkToExprPre(Expr *expr) override {
    if (auto *declRef = dyn_cast<DeclRefExpr>(expr)) {
      // If this decl ref expr was not visited as part of a callExpr and is our
      // target decl... emit a simple async let error.
      if (!visitedCallExprDeclRefExprs.count(declRef)) {
        if (declRef->getDecl() == targetDecl) {
          foundTypeInfo.diagnosticEmitter
              .emitNamedAsyncLetNoIsolationCrossingError(
                  foundTypeInfo.baseLoc, targetDecl->getBaseIdentifier());
          return Action::Continue(expr);
        }
      }
    }

    // If we have a call expr, see if any of its arguments will cause our sent
    // value to be sent into another isolation domain.
    if (auto *callExpr = dyn_cast<CallExpr>(expr)) {
      // Search callExpr's arguments to see if we have our targetDecl.
      auto *argList = callExpr->getArgs();
      for (auto pair : llvm::enumerate(argList->getArgExprs())) {
        auto *arg = lookThroughArgExpr(pair.value());
        auto *declRef = dyn_cast<DeclRefExpr>(arg);
        if (!declRef)
          continue;

        if (declRef->getDecl() != targetDecl)
          continue;

        // Found our target!
        visitedCallExprDeclRefExprs.insert(declRef);

        auto isolationCrossing = callExpr->getIsolationCrossing();

        // If we do not have an isolation crossing, then we must be just sending
        // a value in a nonisolated fashion into an async let. So emit the
        // simple async let error.
        if (!isolationCrossing) {
          foundTypeInfo.diagnosticEmitter
              .emitNamedAsyncLetNoIsolationCrossingError(
                  foundTypeInfo.baseLoc, targetDecl->getBaseIdentifier());
          continue;
        }

        // Otherwise, we are calling an actor-isolated function in the async
        // let. Emit a better error.

        // See if we can find a valueDecl/name for our callee so we can
        // emit a nicer error.
        ConcreteDeclRef concreteDecl =
            callExpr->getDirectCallee()->getReferencedDecl();

        // If we do not find a direct one, see if we are calling a method
        // on a nominal type.
        if (!concreteDecl) {
          if (auto *dot =
                  dyn_cast<DotSyntaxCallExpr>(callExpr->getDirectCallee())) {
            concreteDecl = dot->getSemanticFn()->getReferencedDecl();
          }
        }

        if (!concreteDecl)
          continue;

        auto *valueDecl = concreteDecl.getDecl();
        assert(valueDecl && "Should be non-null if concreteDecl is valid");

        if (auto isolationCrossing = callExpr->getIsolationCrossing()) {
          // If we have an isolation crossing, use that information.
          if (valueDecl->hasName()) {
            foundTypeInfo.diagnosticEmitter.emitNamedIsolationCrossingError(
                foundTypeInfo.baseLoc, targetDecl->getBaseIdentifier(),
                targetDeclIsolationInfo, *isolationCrossing, valueDecl);
            continue;
          }

          // Otherwise default back to the "callee" error.
          foundTypeInfo.diagnosticEmitter.emitNamedIsolationCrossingError(
              foundTypeInfo.baseLoc, targetDecl->getBaseIdentifier(),
              targetDeclIsolationInfo, *isolationCrossing);
          continue;
        }
      }
    }

    return Action::Continue(expr);
  }
};

void UseAfterSendDiagnosticInferrer::infer() {
  // Otherwise, see if our operand's instruction is a sending parameter.
  if (auto fas = FullApplySite::isa(sendingOp->getUser())) {
    assert(!fas.getArgumentConvention(*sendingOp).isIndirectOutParameter() &&
           "We should never send an indirect out parameter");
    if (fas.getArgumentParameterInfo(*sendingOp)
            .hasOption(SILParameterInfo::Sending)) {

      // First try to do the named diagnostic if we can find a name.
      if (auto rootValueAndName = inferNameAndRootHelper(sendingOp->get())) {
        return diagnosticEmitter.emitNamedUseofStronglySentValue(
            baseLoc, rootValueAndName->first);
      }

      // See if we have an ApplyExpr and if we can infer a better type.
      Type type = baseInferredType;
      if (auto *applyExpr =
              sendingOp->getUser()->getLoc().getAsASTNode<ApplyExpr>()) {
        if (auto *foundExpr =
                inferArgumentExprFromApplyExpr(applyExpr, fas, sendingOp))
          type = foundExpr->findOriginalType();
      }

      // Otherwise, emit the typed diagnostic.
      return diagnosticEmitter.emitTypedUseOfStronglySentValue(baseLoc, type);
    }
  }

  auto loc = sendingOp->getUser()->getLoc();

  // If we have a partial_apply that is actor isolated, see if we found a
  // send error due to us sending a value into the partial apply.
  if (auto *ace = loc.getAsASTNode<AbstractClosureExpr>()) {
    if (ace->getActorIsolation().isActorIsolated()) {
      if (initForIsolatedPartialApply(sendingOp, ace)) {
        return;
      }
    }
  }

  if (auto *sourceApply = loc.getAsASTNode<ApplyExpr>()) {
    // Before we do anything further, see if we can find a name and emit a name
    // error.
    if (auto rootValueAndName = inferNameAndRootHelper(sendingOp->get())) {
      auto &state = sendingOpToStateMap.get(sendingOp);
      return diagnosticEmitter.emitNamedIsolationCrossingError(
          baseLoc, rootValueAndName->first,
          state.isolationInfo.getIsolationInfo(),
          *sourceApply->getIsolationCrossing());
    }

    // Otherwise, try to infer from the ApplyExpr.
    return initForApply(sendingOp, sourceApply);
  }

  if (auto fas = FullApplySite::isa(sendingOp->getUser())) {
    if (auto isolationCrossing = fas.getIsolationCrossing()) {
      return diagnosticEmitter.emitTypedIsolationCrossing(
          baseLoc, baseInferredType, *isolationCrossing);
    }
  }

  auto *autoClosureExpr = loc.getAsASTNode<AutoClosureExpr>();
  if (!autoClosureExpr) {
    return diagnosticEmitter.emitUnknownPatternError();
  }

  auto *i = sendingOp->getUser();
  auto pai = ApplySite::isa(i);
  unsigned captureIndex = pai.getASTAppliedArgIndex(*sendingOp);

  auto &state = sendingOpToStateMap.get(sendingOp);
  auto captureInfo =
      autoClosureExpr->getCaptureInfo().getCaptures()[captureIndex];
  auto *captureDecl = captureInfo.getDecl();
  AutoClosureWalker walker(*this, captureDecl,
                           state.isolationInfo.getIsolationInfo());
  autoClosureExpr->walk(walker);
}

// Top level entrypoint for use after send diagnostics.
void SendNonSendableImpl::emitUseAfterSendDiagnostics() {
  auto *function = info->getFunction();
  BasicBlockData<BlockLivenessInfo> blockLivenessInfo(function);
  // We use a generation counter so we can lazily reset blockLivenessInfo
  // since we cannot clear it without iterating over it.
  unsigned blockLivenessInfoGeneration = 0;

  if (sendingOpToRequireInstMultiMap.empty())
    return;

  REGIONBASEDISOLATION_LOG(
      llvm::dbgs() << "Emitting Error. Kind: Use After Send diagnostics.\n");

  for (auto [sendingOp, requireInsts] :
       sendingOpToRequireInstMultiMap.getRange()) {
    REGIONBASEDISOLATION_LOG(
        llvm::dbgs() << "Sending Op. Number: " << sendingOp->getOperandNumber()
                     << ". User: " << *sendingOp->getUser());

    // Then look for our requires before we emit any error. We want to emit a
    // single we don't understand error if we do not find the require.
    bool didEmitRequireNote = false;
    InstructionSet requireInstsUnique(function);
    RequireLiveness liveness(blockLivenessInfoGeneration, sendingOp,
                             blockLivenessInfo);
    ++blockLivenessInfoGeneration;
    liveness.process(requireInsts);

    SmallVector<RequireInst, 8> requireInstsForError;
    for (auto require : requireInsts) {
      // We can have multiple of the same require insts if we had a require
      // and an assign from the same instruction. Our liveness checking
      // above doesn't care about that, but we still need to make sure we do
      // not emit twice.
      if (!requireInstsUnique.insert(*require))
        continue;

      // If this was not a last require, do not emit an error.
      if (!liveness.finalRequires.contains(*require))
        continue;

      requireInstsForError.push_back(require);
      didEmitRequireNote = true;
    }

    // If we did not emit a require, emit an "unknown pattern" error that
    // tells the user to file a bug. This importantly ensures that we can
    // guarantee that we always find the require if we successfully compile.
    if (!didEmitRequireNote) {
      if (shouldAbortOnUnknownPatternMatchError()) {
        llvm::report_fatal_error(
            "RegionIsolation: Aborting on unknown pattern match error");
      }

      diagnoseError(sendingOp, diag::regionbasedisolation_unknown_pattern);
      continue;
    }

    UseAfterSendDiagnosticInferrer diagnosticInferrer(
        sendingOp, requireInstsForError, info->getValueMap(),
        info->getSendingOperandToStateMap());
    diagnosticInferrer.infer();
  }
}

//===----------------------------------------------------------------------===//
//            MARK: Send Never-Sent Diagnostic Inference
//===----------------------------------------------------------------------===//

namespace {

class SendNeverSentDiagnosticEmitter {
  /// The use that actually caused the send.
  Operand *sendingOperand;

  /// The never-sent value that is in the same region as \p
  /// sendingOperand.get().
  llvm::PointerUnion<SILValue, SILInstruction *> neverSent;

  /// The region info that describes the dynamic dataflow derived isolation
  /// region info for the never-sent value.
  ///
  /// This is equal to the merge of the IsolationRegionInfo from all elements in
  /// the never-sent value's region when the error was diagnosed.
  SILDynamicMergedIsolationInfo isolationRegionInfo;

  bool emittedErrorDiagnostic = false;

public:
  SendNeverSentDiagnosticEmitter(
      Operand *sendingOperand,
      llvm::PointerUnion<SILValue, SILInstruction *> neverSent,
      SILDynamicMergedIsolationInfo isolationRegionInfo)
      : sendingOperand(sendingOperand), neverSent(neverSent),
        isolationRegionInfo(isolationRegionInfo) {}

  ~SendNeverSentDiagnosticEmitter() {
    if (!emittedErrorDiagnostic) {
      emitUnknownPatternError();
    } else if (auto proto = isolationRegionInfo.getIsolationInfo()
                   .getIsolatedConformance()) {
       // If the diagnostic comes from a (potentially) isolated conformance,
       // add a note saying so and indicating where the isolated conformance
       // can come in.
       if (auto value = isolationRegionInfo.getIsolationInfo().getIsolatedValue()) {
         if (auto loc = value.getLoc()) {
           diagnoseNote(
               loc, diag::regionbasedisolation_isolated_conformance_introduced,
               proto);
         }
       }
    }
  }

  Operand *getOperand() const { return sendingOperand; }

  SILFunction *getFunction() const { return getOperand()->getFunction(); }

  SILValue getNeverSentValue() const { return neverSent.dyn_cast<SILValue>(); }

  SILInstruction *getNeverSentActorIntroducingInst() const {
    return neverSent.dyn_cast<SILInstruction *>();
  }

  std::optional<DiagnosticBehavior> getBehaviorLimit() const {
    // If the failure is due to an isolated conformance, downgrade the error
    // to a warning prior to Swift 7.
    if (isolationRegionInfo.getIsolationInfo().getIsolatedConformance() &&
        !sendingOperand->get()->getType().getASTType()->getASTContext().LangOpts
          .isSwiftVersionAtLeast(7))
      return DiagnosticBehavior::Warning;

    return sendingOperand->get()->getType().getConcurrencyDiagnosticBehavior(
        getOperand()->getFunction());
  }

  /// Attempts to retrieve and return the callee declaration.
  std::optional<const ValueDecl *> getSendingCallee() const {
    return getSendingApplyCallee(sendingOperand->getUser());
  }

  SILLocation getLoc() const { return sendingOperand->getUser()->getLoc(); }

  /// Return the isolation region info for \p getNeverSentValue().
  SILDynamicMergedIsolationInfo getIsolationRegionInfo() const {
    return isolationRegionInfo;
  }

  void emitUnknownPatternError() {
    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(getOperand()->getUser(),
                  diag::regionbasedisolation_unknown_pattern)
        .limitBehaviorIf(getBehaviorLimit());
  }

  void emitUnknownUse(SILLocation loc) {
    // TODO: This will eventually be an unknown pattern error.
    diagnoseError(loc, diag::regionbasedisolation_task_or_actor_isolated_sent)
        .limitBehaviorIf(getBehaviorLimit());
  }

  void emitPassToApply(SILLocation loc, Type inferredType,
                       ApplyIsolationCrossing crossing) {
    diagnoseError(loc, diag::regionbasedisolation_type_send_yields_race,
                  inferredType)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());
    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), crossing.getCalleeIsolation());

    if (auto callee = getSendingCallee()) {
      diagnoseNote(
          loc,
          diag::regionbasedisolation_typed_sendneversendable_via_arg_callee,
          descriptiveKindStr, inferredType, calleeIsolationStr, callee.value());
    } else {
      diagnoseNote(loc,
                   diag::regionbasedisolation_typed_sendneversendable_via_arg,
                   descriptiveKindStr, inferredType, calleeIsolationStr);
    }
  }

  void emitNamedFunctionArgumentClosure(SILLocation loc, Identifier name,
                                        ApplyIsolationCrossing crossing) {
    emitNamedOnlyError(loc, name);

    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());
    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), crossing.getCalleeIsolation());
    auto callerIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), crossing.getCallerIsolation());
    bool isDisconnected = getIsolationRegionInfo().isDisconnected();
    diagnoseNote(loc,
                 diag::regionbasedisolation_named_isolated_closure_yields_race,
                 isDisconnected, descriptiveKindStr, name, calleeIsolationStr,
                 callerIsolationStr)
        .highlight(loc.getSourceRange());
  }

  void emitTypedSendingNeverSendableToSendingParam(SILLocation loc,
                                                   Type inferredType) {
    diagnoseError(loc, diag::regionbasedisolation_type_send_yields_race,
                  inferredType)
        .highlight(loc.getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());

    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());

    if (auto callee = getSendingCallee()) {
      diagnoseNote(
          loc, diag::regionbasedisolation_typed_tns_passed_to_sending_callee,
          descriptiveKindStr, inferredType, callee.value());
    } else {
      diagnoseNote(loc, diag::regionbasedisolation_typed_tns_passed_to_sending,
                   descriptiveKindStr, inferredType);
    }
  }

  /// Emit an error for a case where we have captured a value like an actor and
  /// thus a sending closure has become actor isolated (and thus unable to be
  /// sent).
  void emitClosureErrorWithCapturedActor(Operand *partialApplyOp,
                                         Operand *actualUse,
                                         SILArgument *fArg) {
    auto descriptiveKindStr =
        getIsolationRegionInfo().printForCodeDiagnostic(getFunction());

    diagnoseError(partialApplyOp,
                  diag::regionbasedisolation_typed_tns_passed_sending_closure,
                  descriptiveKindStr)
        .limitBehaviorIf(getDiagnosticBehaviorLimitForOperands(
            actualUse->getFunction(), {actualUse}));

    descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());
    diagnoseNote(actualUse, diag::regionbasedisolation_closure_captures_actor,
                 fArg->getDecl()->getName(), descriptiveKindStr);
  }

  /// Emit a typed error for an isolated closure being passed as a sending
  /// parameter.
  ///
  /// \arg partialApplyOp the operand of the outermost partial apply.
  /// \arg actualUse the operand inside the closure that actually caused the
  /// capture to occur. This maybe inside a different function from the partial
  /// apply since we want to support a use inside a recursive closure.
  void emitSendingClosureParamDirectlyIsolated(Operand *partialApplyOp,
                                               Operand *actualUse,
                                               SILArgument *fArg) {
    auto descriptiveKindStr =
        getIsolationRegionInfo().printForCodeDiagnostic(getFunction());

    diagnoseError(partialApplyOp,
                  diag::regionbasedisolation_typed_tns_passed_sending_closure,
                  descriptiveKindStr)
        .limitBehaviorIf(getDiagnosticBehaviorLimitForOperands(
            actualUse->getFunction(), {actualUse}));

    // If we have a closure capture box, emit a special diagnostic.
    if (getIsolationRegionInfo().getIsolationInfo().isTaskIsolated()) {
      if (cast<SILFunctionArgument>(fArg)->isClosureCapture() &&
          fArg->getType().is<SILBoxType>()) {
        auto diag = diag::
            regionbasedisolation_typed_tns_passed_to_sending_closure_helper_have_boxed_value_task_isolated;
        diagnoseNote(actualUse, diag, fArg->getDecl());
        return;
      }

      auto diag = diag::
          regionbasedisolation_typed_tns_passed_to_sending_closure_helper_have_value_task_isolated;
      diagnoseNote(actualUse, diag, fArg->getDecl()->getName());
      return;
    }

    descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());

    auto diag = diag::
        regionbasedisolation_typed_tns_passed_to_sending_closure_helper_have_value;
    diagnoseNote(actualUse, diag, descriptiveKindStr,
                 fArg->getDecl()->getName());
  }

  void emitSendingClosureMultipleCapturedOperandError(
      SILLocation loc, ArrayRef<Operand *> capturedOperands) {
    // Our caller should have passed at least one operand. Emit an unknown error
    // to signal we need a bug report.
    if (capturedOperands.empty()) {
      emitUnknownPatternError();
      return;
    }

    auto descriptiveKindStr =
        getIsolationRegionInfo()->printForCodeDiagnostic(getFunction());

    auto emitMainError = [&] {
      auto behaviorLimit = getDiagnosticBehaviorLimitForOperands(
          getFunction(), capturedOperands);
      diagnoseError(loc,
                    diag::regionbasedisolation_typed_tns_passed_sending_closure,
                    descriptiveKindStr)
          .highlight(loc.getSourceRange())
          .limitBehaviorIf(behaviorLimit);
    };

    if (capturedOperands.size() == 1) {
      auto captured = capturedOperands.front();
      auto actualUseInfo = findClosureUse(captured);

      // If we fail to find actual use info, emit an unknown error.
      if (!actualUseInfo) {
        emitUnknownPatternError();
        return;
      }

      if (getIsolationRegionInfo()->isTaskIsolated()) {
        emitMainError();
        auto diag = diag::
            regionbasedisolation_typed_tns_passed_to_sending_closure_helper_have_value_task_isolated;
        diagnoseNote(actualUseInfo->first, diag,
                     actualUseInfo->second->getDecl()->getName());
        return;
      }

      emitMainError();
      descriptiveKindStr =
          getIsolationRegionInfo().printForDiagnostics(getFunction());
      auto diag = diag::
          regionbasedisolation_typed_tns_passed_to_sending_closure_helper_have_value_region;
      diagnoseNote(actualUseInfo->first, diag, descriptiveKindStr,
                   actualUseInfo->second->getDecl()->getName());
      return;
    }

    emitMainError();

    bool emittedDiagnostic = false;
    for (auto captured : capturedOperands) {
      auto actualUseInfo = findClosureUse(captured);
      if (!actualUseInfo)
        continue;
      emittedDiagnostic = true;
      auto diag = diag::
          regionbasedisolation_typed_tns_passed_to_sending_closure_helper_multiple_value;
      diagnoseNote(actualUseInfo->first, diag,
                   actualUseInfo->second->getDecl()->getName());
    }

    // Check if we did not emit a diagnostic. In such a case, we need to emit an
    // unknown patten error so that we get a bug report from the user.
    if (!emittedDiagnostic) {
      emitUnknownPatternError();
    }
  }

  void emitNamedOnlyError(SILLocation loc, Identifier name) {
    diagnoseError(loc, diag::regionbasedisolation_named_send_yields_race, name)
        .highlight(getOperand()->getUser()->getLoc().getSourceRange())
        .limitBehaviorIf(getBehaviorLimit());
  }

  void emitNamedAsyncLetCapture(SILLocation loc, Identifier name,
                                SILIsolationInfo sentValueIsolation) {
    assert(!getIsolationRegionInfo().isDisconnected() &&
           "Should never be disconnected?!");
    emitNamedOnlyError(loc, name);

    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());

    diagnoseNote(loc, diag::regionbasedisolation_named_send_nt_asynclet_capture,
                 name, descriptiveKindStr);
  }

  void emitNamedIsolation(SILLocation loc, Identifier name,
                          ApplyIsolationCrossing isolationCrossing) {
    emitNamedOnlyError(loc, name);

    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());
    auto calleeIsolationStr =
        SILIsolationInfo::printActorIsolationForDiagnostics(
            getFunction(), isolationCrossing.getCalleeIsolation());
    bool isDisconnected = getIsolationRegionInfo().isDisconnected();

    if (auto callee = getSendingCallee()) {
      diagnoseNote(loc,
                   diag::regionbasedisolation_named_send_never_sendable_callee,
                   isDisconnected, name, descriptiveKindStr, calleeIsolationStr,
                   callee.value(), descriptiveKindStr);
    } else {
      diagnoseNote(loc, diag::regionbasedisolation_named_send_never_sendable,
                   isDisconnected, name, descriptiveKindStr, calleeIsolationStr,
                   descriptiveKindStr);
    }
  }

  void emitNamedSendingNeverSendableToSendingParam(SILLocation loc,
                                                   Identifier varName) {
    emitNamedOnlyError(loc, varName);

    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());
    bool isDisconnected = getIsolationRegionInfo().isDisconnected();
    auto diag = diag::regionbasedisolation_named_send_into_sending_param;
    diagnoseNote(loc, diag, isDisconnected, descriptiveKindStr, varName);
  }

  void emitNamedSendingReturn(SILLocation loc, Identifier varName) {
    emitNamedOnlyError(loc, varName);
    auto descriptiveKindStr =
        getIsolationRegionInfo().printForDiagnostics(getFunction());
    bool isDisconnected = getIsolationRegionInfo().isDisconnected();
    auto diag = diag::regionbasedisolation_named_nosend_send_into_result;
    diagnoseNote(loc, diag, isDisconnected, descriptiveKindStr, varName,
                 descriptiveKindStr);
  }

private:
  ASTContext &getASTContext() const {
    return getOperand()->getFunction()->getASTContext();
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SourceLoc loc, Diag<T...> diag,
                                   U &&...args) {
    emittedErrorDiagnostic = true;
    return std::move(getASTContext()
                         .Diags.diagnose(loc, diag, std::forward<U>(args)...)
                         .warnUntilSwiftVersion(6));
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILLocation loc, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILInstruction *inst, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(Operand *op, Diag<T...> diag, U &&...args) {
    return diagnoseError(op->getUser()->getLoc(), diag,
                         std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SourceLoc loc, Diag<T...> diag, U &&...args) {
    return getASTContext().Diags.diagnose(loc, diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILLocation loc, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILInstruction *inst, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(Operand *op, Diag<T...> diag, U &&...args) {
    return diagnoseNote(op->getUser()->getLoc(), diag,
                        std::forward<U>(args)...);
  }
};

class SentNeverSendableDiagnosticInferrer {
  struct AutoClosureWalker;

  RegionAnalysisValueMap &valueMap;
  SendNeverSentDiagnosticEmitter diagnosticEmitter;

  using SentNeverSendableError = PartitionOpError::SentNeverSendableError;

public:
  SentNeverSendableDiagnosticInferrer(RegionAnalysisValueMap &valueMap,
                                      SentNeverSendableError error)
      : valueMap(valueMap),
        diagnosticEmitter(error.op->getSourceOp(),
                          valueMap.getRepresentative(error.sentElement),
                          error.isolationRegionInfo) {}

  /// Gathers diagnostics. Returns false if we emitted a "I don't understand
  /// error". If we emit such an error, we should bail without emitting any
  /// further diagnostics, since we may not have any diagnostics or be in an
  /// inconcistent state.
  bool run();

private:
  /// \p actualCallerIsolation is used to override the caller isolation we use
  /// when emitting the error if the closure would have the incorrect one.
  bool initForIsolatedPartialApply(
      Operand *op, AbstractClosureExpr *ace,
      std::optional<ActorIsolation> actualCallerIsolation = {});

  bool initForSendingPartialApply(FullApplySite fas, Operand *pai);

  std::optional<unsigned>
  getIsolatedValuePartialApplyIndex(PartialApplyInst *pai,
                                    SILValue isolatedValue) {
    for (auto &paiOp : ApplySite(pai).getArgumentOperands()) {
      if (valueMap.getTrackableValue(paiOp.get()).value.getRepresentative() ==
          isolatedValue) {
        return ApplySite(pai).getASTAppliedArgIndex(paiOp);
      }
    }

    return {};
  }
};

} // namespace

bool SentNeverSendableDiagnosticInferrer::initForSendingPartialApply(
    FullApplySite fas, Operand *callsiteOp) {
  // This is the partial apply that is being passed as a sending parameter.
  auto *sendingPAI =
      dyn_cast<PartialApplyInst>(stripFunctionConversions(callsiteOp->get()));
  if (!sendingPAI)
    return false;

  // Make sure that we only handle closure literals.
  //
  // TODO: This should be marked on closures at the SIL level... I shouldn't
  // have to refer to the AST.
  if (!sendingPAI->getLoc().getAsASTNode<ClosureExpr>())
    return false;

  // Ok, we have a closure literal. First we handle a potential capture of
  // 'self' before we do anything by looping over our captured parameters.
  //
  // DISCUSSION: The reason why we do this early is that as a later heuristic,
  // we check if any of the values are directly task isolated (i.e. they are
  // actually the task isolated value, not a value that is in the same region as
  // something that is task isolated). This could potentially result in us
  // emitting a task isolated error instead of an actor isolated error here if
  // for some reason SILGen makes the self capture come later in the capture
  // list. From a compile time perspective, going over a list of captures twice
  // is not going to hurt especially since we are going to emit a diagnostic
  // here anyways.
  for (auto &sendingPAIOp : sendingPAI->getArgumentOperands()) {
    // NOTE: If we access a field on self in the closure, we will still just
    // capture self... so we do not have to handle that case due to the way
    // SILGen codegens today. This is also true if we use a capture list [x =
    // self.field] (i.e. a closure that captures a field from self is still
    // nonisolated).
    if (!sendingPAIOp.get()->getType().isAnyActor())
      continue;

    auto *fArg = dyn_cast<SILFunctionArgument>(
        lookThroughOwnershipInsts(sendingPAIOp.get()));
    if (!fArg || !fArg->isSelf())
      continue;

    auto capturedValue = findClosureUse(&sendingPAIOp);
    if (!capturedValue) {
      // If we failed to find the direct capture of self, emit an unknown code
      // pattern error so the user knows to send a bug report. This should never
      // fail.
      diagnosticEmitter.emitUnknownPatternError();
      return true;
    }

    // Otherwise, emit our captured actor error.
    diagnosticEmitter.emitClosureErrorWithCapturedActor(
        &sendingPAIOp, capturedValue->first, capturedValue->second);
    return true;
  }

  // Ok, we know that we have a closure expr. We now need to find the specific
  // closure captured value that is actor or task isolated. Then we search for
  // the potentially recursive closure use so we can show a nice loc to the
  // user.
  auto maybeIsolatedValue =
      diagnosticEmitter.getIsolationRegionInfo()->maybeGetIsolatedValue();

  // If we do not find an actual task isolated value while looping below, this
  // contains the non sendable captures of the partial apply that we want to
  // emit a more heuristic based error for. See documentation below.
  SmallVector<Operand *, 8> nonSendableOps;

  for (auto &sendingPAIOp : sendingPAI->getArgumentOperands()) {
    // If our value's rep is task isolated or is the dynamic isolated
    // value... then we are done. This is a 'correct' error value to emit.
    auto trackableValue = valueMap.getTrackableValue(sendingPAIOp.get());
    if (trackableValue.value.isSendable())
      continue;

    auto rep = trackableValue.value.getRepresentative().maybeGetValue();
    nonSendableOps.push_back(&sendingPAIOp);

    if (trackableValue.value.getIsolationRegionInfo().isTaskIsolated() ||
        rep == maybeIsolatedValue) {
      if (auto capturedValue = findClosureUse(&sendingPAIOp)) {
        diagnosticEmitter.emitSendingClosureParamDirectlyIsolated(
            callsiteOp, capturedValue->first, capturedValue->second);
        return true;
      }
    }
  }

  // If we did not find a clear answer in terms of an isolated value, we emit a
  // more general error based on:
  //
  // 1. If we have one non-Sendable value then we know that must be the value.
  // 2. Otherwise, we emit a generic captured non-Sendable value error to give
  //    people something to work off of.
  diagnosticEmitter.emitSendingClosureMultipleCapturedOperandError(
      callsiteOp->getUser()->getLoc(), nonSendableOps);
  return true;
}

bool SentNeverSendableDiagnosticInferrer::initForIsolatedPartialApply(
    Operand *op, AbstractClosureExpr *ace,
    std::optional<ActorIsolation> actualCallerIsolation) {
  auto diagnosticPair = findClosureUse(op);
  if (!diagnosticPair)
    return false;

  auto *diagnosticOp = diagnosticPair->first;

  ApplyIsolationCrossing crossing(
      *op->getFunction()->getActorIsolation(),
      *diagnosticOp->getFunction()->getActorIsolation());

  // We do not need to worry about failing to infer a name here since we are
  // going to be returning some form of a SILFunctionArgument which is always
  // easy to find a name for.
  if (auto rootValueAndName = inferNameAndRootHelper(op->get())) {
    diagnosticEmitter.emitNamedFunctionArgumentClosure(
        diagnosticOp->getUser()->getLoc(), rootValueAndName->first, crossing);
    return true;
  }

  return false;
}

/// This walker visits an AutoClosureExpr and looks for uses of a specific
/// captured value. We want to error on the uses in the autoclosure.
struct SentNeverSendableDiagnosticInferrer::AutoClosureWalker : ASTWalker {
  SendNeverSentDiagnosticEmitter &foundTypeInfo;
  ValueDecl *targetDecl;
  SILIsolationInfo targetDeclIsolationInfo;
  SmallPtrSet<Expr *, 8> visitedCallExprDeclRefExprs;
  SILLocation captureLoc;
  bool isAsyncLet;

  AutoClosureWalker(SendNeverSentDiagnosticEmitter &foundTypeInfo,
                    ValueDecl *targetDecl,
                    SILIsolationInfo targetDeclIsolationInfo,
                    SILLocation captureLoc, bool isAsyncLet)
      : foundTypeInfo(foundTypeInfo), targetDecl(targetDecl),
        targetDeclIsolationInfo(targetDeclIsolationInfo),
        captureLoc(captureLoc), isAsyncLet(isAsyncLet) {}

  Expr *lookThroughArgExpr(Expr *expr) {
    while (true) {
      if (auto *memberRefExpr = dyn_cast<MemberRefExpr>(expr)) {
        expr = memberRefExpr->getBase();
        continue;
      }

      if (auto *cvt = dyn_cast<ImplicitConversionExpr>(expr)) {
        expr = cvt->getSubExpr();
        continue;
      }

      if (auto *e = dyn_cast<ForceValueExpr>(expr)) {
        expr = e->getSubExpr();
        continue;
      }

      if (auto *t = dyn_cast<TupleElementExpr>(expr)) {
        expr = t->getBase();
        continue;
      }

      return expr;
    }
  }

  PreWalkResult<Expr *> walkToExprPre(Expr *expr) override {
    if (auto *declRef = dyn_cast<DeclRefExpr>(expr)) {
      // If this decl ref expr was not visited as part of a callExpr and is our
      // target decl... emit a simple async let error.
      //
      // This occurs if we do:
      //
      // ```
      // let x = ...
      // async let y = x
      // ```
      if (declRef->getDecl() == targetDecl) {
        foundTypeInfo.emitNamedAsyncLetCapture(captureLoc,
                                               targetDecl->getBaseIdentifier(),
                                               targetDeclIsolationInfo);
        return Action::Continue(expr);
      }
    }

    return Action::Continue(expr);
  }
};

bool SentNeverSendableDiagnosticInferrer::run() {
  // We need to find the isolation info.
  auto *op = diagnosticEmitter.getOperand();
  auto loc = op->getUser()->getLoc();

  if (auto *sourceApply = loc.getAsASTNode<ApplyExpr>()) {
    // First see if we have a 'sending' argument.
    if (auto fas = FullApplySite::isa(op->getUser())) {
      if (fas.getArgumentParameterInfo(*op).hasOption(
              SILParameterInfo::Sending)) {
        // Before we do anything, lets see if we are passing a sendable closure
        // literal. If we do, we want to emit a special error that states which
        // captured value caused the actual error.
        if (initForSendingPartialApply(fas, op))
          return true;

        // See if we can infer a name from the value.
        if (auto varName = inferNameHelper(op->get())) {
          diagnosticEmitter.emitNamedSendingNeverSendableToSendingParam(
              loc, *varName);
          return true;
        }

        Type type = op->get()->getType().getASTType();
        if (auto *inferredArgExpr =
                inferArgumentExprFromApplyExpr(sourceApply, fas, op)) {
          type = inferredArgExpr->findOriginalType();
        }

        diagnosticEmitter.emitTypedSendingNeverSendableToSendingParam(loc,
                                                                      type);
        return true;
      }
    }

    // First try to get the apply from the isolation crossing.
    auto isolation = sourceApply->getIsolationCrossing();

    // If we could not infer an isolation...
    if (!isolation) {
      // Otherwise, emit a "we don't know error" that tells the user to file a
      // bug.
      diagnosticEmitter.emitUnknownPatternError();
      return false;
    }
    assert(isolation && "Expected non-null");

    // Then if we are calling a closure expr. If so, we should use the loc of
    // the closure.
    if (auto *closureExpr =
            dyn_cast<AbstractClosureExpr>(sourceApply->getFn())) {
      initForIsolatedPartialApply(op, closureExpr,
                                  isolation->getCallerIsolation());
      return true;
    }

    // See if we can infer a name from the value.
    if (auto name = inferNameHelper(op->get())) {
      diagnosticEmitter.emitNamedIsolation(loc, *name, *isolation);
      return true;
    }

    // Attempt to find the specific sugared ASTType if we can to emit a better
    // diagnostic.
    Type type = op->get()->getType().getASTType();
    if (auto fas = FullApplySite::isa(op->getUser())) {
      if (auto *inferredArgExpr =
              inferArgumentExprFromApplyExpr(sourceApply, fas, op)) {
        type = inferredArgExpr->findOriginalType();
      }
    }

    diagnosticEmitter.emitPassToApply(loc, type, *isolation);
    return true;
  }

  if (auto *ace = loc.getAsASTNode<AbstractClosureExpr>()) {
    if (ace->getActorIsolation().isActorIsolated()) {
      if (initForIsolatedPartialApply(op, ace)) {
        return true;
      }
    }
  }

  // See if we are in SIL and have an apply site specified isolation.
  if (auto fas = FullApplySite::isa(op->getUser())) {
    if (auto isolation = fas.getIsolationCrossing()) {
      diagnosticEmitter.emitPassToApply(loc, op->get()->getType().getASTType(),
                                        *isolation);
      return true;
    }
  }

  if (auto *ri = dyn_cast<ReturnInst>(op->getUser())) {
    auto fType = ri->getFunction()->getLoweredFunctionType();
    if (fType->getNumResults() &&
        fType->getResults()[0].hasOption(SILResultInfo::IsSending)) {
      assert(llvm::all_of(fType->getResults(),
                          [](SILResultInfo resultInfo) {
                            return resultInfo.hasOption(
                                SILResultInfo::IsSending);
                          }) &&
             "All result info must be the same... if that changes... update "
             "this code!");
      if (auto name = inferNameHelper(op->get())) {
        diagnosticEmitter.emitNamedSendingReturn(loc, *name);
        return true;
      }
    } else {
      assert(llvm::none_of(fType->getResults(),
                           [](SILResultInfo resultInfo) {
                             return resultInfo.hasOption(
                                 SILResultInfo::IsSending);
                           }) &&
             "All result info must be the same... if that changes... update "
             "this code!");
    }
  }

  // If we are failing due to an autoclosure... see if we can find the captured
  // value that is causing the issue.
  if (auto *autoClosureExpr = loc.getAsASTNode<AutoClosureExpr>()) {
    // To split up this work, we only do this for async let for now.
    if (autoClosureExpr->getThunkKind() == AutoClosureExpr::Kind::AsyncLet) {
      auto *i = op->getUser();
      auto pai = ApplySite::isa(i);
      unsigned captureIndex = pai.getASTAppliedArgIndex(*op);
      auto captureInfo =
          autoClosureExpr->getCaptureInfo().getCaptures()[captureIndex];
      auto loc = RegularLocation(captureInfo.getLoc(), false /*implicit*/);
      AutoClosureWalker walker(
          diagnosticEmitter, captureInfo.getDecl(),
          diagnosticEmitter.getIsolationRegionInfo().getIsolationInfo(), loc,
          autoClosureExpr->getThunkKind() == AutoClosureExpr::Kind::AsyncLet);
      autoClosureExpr->walk(walker);
      return true;
    }
  }

  diagnosticEmitter.emitUnknownUse(loc);
  return true;
}

//===----------------------------------------------------------------------===//
//               MARK: InOutSendingReturnedError Error Emitter
//===----------------------------------------------------------------------===//

namespace {

class InOutSendingReturnedDiagnosticEmitter {
  /// A region analysis function info that we use if we need to determine which
  /// incoming block edge had an error upon it.
  RegionAnalysisFunctionInfo *raFuncInfo;

  /// The function exiting inst where the 'inout sending' parameter was actor
  /// isolated.
  TermInst *functionExitingInst;

  /// The 'inout sending' param that we are emitting an error for.
  SILValue inoutSendingParam;

  /// The element number of the 'inout sending' param.
  Element inoutSendingParamElement;

  /// If we did not return the 'inout sending' param directly but instead
  /// returned something else in the same region. This is that value.
  ///
  /// If we actually returned the inout sending parameter this is SILValue().
  SILValue returnedValue;

  /// If we had a failure due to returning a value that is actor isolated due to
  /// it being in the same region as an out parameter. THis is the actor
  /// isolation.
  SILDynamicMergedIsolationInfo isolationInfo;

  bool emittedErrorDiagnostic = false;

public:
  class LastValueEnum;

  InOutSendingReturnedDiagnosticEmitter(
      RegionAnalysisFunctionInfo *raFuncInfo, TermInst *functionExitingInst,
      SILValue inoutSendingParam, Element inoutSendingParamElement,
      SILValue erroringValue, SILDynamicMergedIsolationInfo isolationInfo)
      : raFuncInfo(raFuncInfo), functionExitingInst(functionExitingInst),
        inoutSendingParam(inoutSendingParam),
        inoutSendingParamElement(inoutSendingParamElement),
        returnedValue(erroringValue), isolationInfo(isolationInfo) {}

  ~InOutSendingReturnedDiagnosticEmitter() {
    // If we were supposed to emit a diagnostic and didn't emit an unknown
    // pattern error.
    if (!emittedErrorDiagnostic)
      emitUnknownPatternError();
  }

  SILFunction *getFunction() const { return inoutSendingParam->getFunction(); }

  std::optional<DiagnosticBehavior> getBehaviorLimit() const {
    return inoutSendingParam->getType().getConcurrencyDiagnosticBehavior(
        getFunction());
  }

  void emitUnknownPatternError() {
    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(functionExitingInst,
                  diag::regionbasedisolation_unknown_pattern)
        .limitBehaviorIf(getBehaviorLimit());
  }

  void emit();

  /// Called if we return the actual inout sending value.
  void emitReturnInOutSendingError(SILDynamicMergedIsolationInfo isolationInfo,
                                   SILLocation loc) {
    // We should always be able to find a name for an inout sending param. If we
    // do not, emit an unknown pattern error.
    auto inoutSendingParamName = inferNameHelper(inoutSendingParam);
    if (!inoutSendingParamName) {
      return emitUnknownPatternError();
    }

    diagnoseError(
        loc, diag::regionbasedisolation_inout_sending_cannot_be_returned_param,
        *inoutSendingParamName)
        .limitBehaviorIf(getBehaviorLimit());
    if (isolationInfo->isActorIsolated()) {
      diagnoseNote(
          loc,
          diag::
              regionbasedisolation_inout_sending_cannot_be_returned_note_actor_param,
          *inoutSendingParamName,
          isolationInfo->printForDiagnostics(getFunction()));
      return;
    }
    diagnoseNote(
        loc,
        diag::regionbasedisolation_inout_sending_cannot_be_returned_note_param,
        *inoutSendingParamName);
  }

  void emitValueError(SILValue value,
                      SILDynamicMergedIsolationInfo isolationInfo,
                      SILLocation loc) {
    // We should always be able to find a name for an inout sending param. If we
    // do not, emit an unknown pattern error.
    auto inoutSendingParamName = inferNameHelper(inoutSendingParam);
    if (!inoutSendingParamName) {
      return emitUnknownPatternError();
    }

    std::optional<Identifier> erroringEltName = inferNameHelper(value);
    if (!erroringEltName) {
      return emitUnknownPatternError();
    }

    diagnoseError(
        loc, diag::regionbasedisolation_inout_sending_cannot_be_returned_value,
        *erroringEltName)
        .limitBehaviorIf(getBehaviorLimit());
    if (isolationInfo->isActorIsolated()) {
      diagnoseNote(
          loc,
          diag::
              regionbasedisolation_inout_sending_cannot_be_returned_note_actor_value,
          *erroringEltName, *inoutSendingParamName,
          isolationInfo->printForDiagnostics(getFunction()));
      return;
    }
    diagnoseNote(
        loc,
        diag::regionbasedisolation_inout_sending_cannot_be_returned_note_value,
        *erroringEltName, *inoutSendingParamName);
  }

  /// Print \p value in a standard way. Allow for loc to override the specific
  /// location used to emit the diagnostic fi non-standard.
  void emitLastValueEnum(const LastValueEnum &value,
                         SILDynamicMergedIsolationInfo isolationInfo,
                         SILLocation loc = SILLocation::invalid());

  /// Emit an error for use when we are processing the incoming value of a phi
  /// argument or of the dynamic value of an indirect out parameter.
  bool emitOutParamIncomingValueError(const LastValueEnum &value);

  void emitDeclRefError(SILDeclRef declRef,
                        SILDynamicMergedIsolationInfo isolationInfo,
                        SILLocation loc) {
    // We should always be able to find a name for an inout sending param. If we
    // do not, emit an unknown pattern error.
    auto inoutSendingParamName = inferNameHelper(inoutSendingParam);
    if (!inoutSendingParamName) {
      return emitUnknownPatternError();
    }

    diagnoseError(
        loc,
        diag::
            regionbasedisolation_inout_sending_cannot_be_returned_value_result,
        declRef.getAbstractFunctionDecl())
        .limitBehaviorIf(getBehaviorLimit());

    if (isolationInfo->isActorIsolated()) {
      diagnoseNote(
          loc,
          diag::
              regionbasedisolation_inout_sending_cannot_be_returned_note_actor_return_value,
          declRef.getAbstractFunctionDecl(), *inoutSendingParamName,
          isolationInfo.printForDiagnostics(getFunction()));
      return;
    }
    diagnoseNote(
        loc,
        diag::
            regionbasedisolation_inout_sending_cannot_be_returned_note_return_value,
        declRef.getAbstractFunctionDecl(), *inoutSendingParamName);
  }

  ASTContext &getASTContext() const {
    return functionExitingInst->getFunction()->getASTContext();
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SourceLoc loc, Diag<T...> diag,
                                   U &&...args) {
    emittedErrorDiagnostic = true;
    return std::move(getASTContext()
                         .Diags.diagnose(loc, diag, std::forward<U>(args)...)
                         .warnUntilSwiftVersion(6));
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILLocation loc, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILInstruction *inst, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SourceLoc loc, Diag<T...> diag, U &&...args) {
    return getASTContext().Diags.diagnose(loc, diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILLocation loc, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILInstruction *inst, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(inst->getLoc(), diag, std::forward<U>(args)...);
  }
};

} // namespace

static SILValue lookThroughAccess(SILValue value) {
  while (true) {
    // We look through access, copies, and loads.
    if (auto *bai = dyn_cast<BeginAccessInst>(value)) {
      value = bai->getOperand();
      continue;
    }

    if (auto *cvi = dyn_cast<CopyValueInst>(value)) {
      value = cvi->getOperand();
      continue;
    }

    if (auto *bbi = dyn_cast<BeginBorrowInst>(value);
        bbi && !bbi->isFromVarDecl()) {
      value = bbi->getOperand();
      continue;
    }

    if (auto *mvi = dyn_cast<MoveValueInst>(value);
        mvi && !mvi->isFromVarDecl()) {
      value = mvi->getOperand();
      continue;
    }

    if (auto *li = dyn_cast<LoadInst>(value)) {
      value = li->getOperand();
      continue;
    }

    if (auto *lbi = dyn_cast<LoadBorrowInst>(value)) {
      value = lbi->getOperand();
      continue;
    }

    return value;
  }
}

class InOutSendingReturnedDiagnosticEmitter::LastValueEnum {
public:
  enum Kind {
    None,
    ApplySite,
    CopyAddr,
    Store,
    Value,
    ReturnTerm,
  };

private:
  Kind kind;
  std::variant<FullApplySite, SILValue, CopyAddrInst *, StoreInst *, Operand *>
      value;

  LastValueEnum() : kind(Kind::None), value() {}
  LastValueEnum(FullApplySite inst) : kind(Kind::ApplySite), value(inst) {}
  LastValueEnum(SILValue value) : kind(Kind::Value), value(value) {}
  LastValueEnum(CopyAddrInst *inst) : kind(Kind::CopyAddr), value(inst) {}
  LastValueEnum(StoreInst *inst) : kind(Kind::Store), value(inst) {}
  LastValueEnum(Operand *branchUse) : kind(Kind::ReturnTerm), value(branchUse) {
    assert(isa<TermInst>(branchUse->getUser()));
    assert(branchUse->getUser()->getLoc().getKind() == SILLocation::ReturnKind);
  }

public:
  static LastValueEnum get(SILValue value);
  static LastValueEnum get(SILInstruction *inst);
  static LastValueEnum get(Operand *use);
  static bool isSupported(Operand *use);

  operator bool() const { return getKind() != Kind::None; }

  Kind getKind() const { return kind; }
  bool isApplySite() const { return getKind() == Kind::ApplySite; }
  bool isValue() const { return getKind() == Kind::Value; }
  bool isStore() const { return getKind() == Kind::Store; }
  bool isCopyAddr() const { return getKind() == Kind::CopyAddr; }

  /// Is this a terminator instruction that is an incoming value to an epilogue
  /// block and thus forms part of the return from a function.
  bool isReturnTerm() const { return getKind() == Kind::ReturnTerm; }

  FullApplySite getFullApplySite() const {
    return std::get<FullApplySite>(value);
  }
  SILDeclRef getDeclRef() const {
    return getFullApplySite().getCalleeFunction()->getDeclRef();
  }
  SILValue getValue() const {
    switch (getKind()) {
    case None:
    case ApplySite:
      return SILValue();
    case CopyAddr:
      return getCopyAddr()->getAllOperands()[CopyLikeInstruction::Src].get();
    case Store:
      return getStore()->getAllOperands()[CopyLikeInstruction::Src].get();
    case Value:
      return std::get<SILValue>(value);
    case ReturnTerm:
      return std::get<Operand *>(value)->get();
    }
  }
  CopyAddrInst *getCopyAddr() const { return std::get<CopyAddrInst *>(value); }
  StoreInst *getStore() const { return std::get<StoreInst *>(value); }
  Operand *getReturnTerm() const { return std::get<Operand *>(value); }

  SILBasicBlock *getParentBlock() const {
    switch (getKind()) {
    case None:
      return nullptr;
    case ApplySite:
      return getFullApplySite()->getParent();
    case Value:
      return getValue()->getParentBlock();
    case CopyAddr:
      return getCopyAddr()->getParentBlock();
    case Store:
      return getStore()->getParentBlock();
    case ReturnTerm:
      return getReturnTerm()->getParentBlock();
    }
  }

  SILInstruction *getDefiningInsertionPoint() const {
    switch (getKind()) {
    case None:
      return nullptr;
    case ApplySite:
      return *getFullApplySite();
    case Value:
      return getValue()->getDefiningInsertionPoint();
    case CopyAddr:
      return getCopyAddr();
    case Store:
      return getStore();
    case ReturnTerm:
      return getReturnTerm()->getUser();
    }
  }

  SILLocation getLoc() const {
    switch (getKind()) {
    case None:
      return SILLocation::invalid();
    case ApplySite:
    case Value:
    case CopyAddr:
    case Store:
    case ReturnTerm:
      return getDefiningInsertionPoint()->getLoc();
    }
  }

  bool operator==(SILValue otherValue) const {
    switch (getKind()) {
    case None:
    case ApplySite:
      return false;
    case CopyAddr:
    case Store:
    case Value:
    case ReturnTerm:
      return lookThroughAccess(getValue()) == lookThroughAccess(otherValue);
    }
  }

  static bool
  findLastValuesForOutParam(SILFunctionArgument *fArg,
                            SmallVectorImpl<LastValueEnum> &lastValues);

  void print(llvm::raw_ostream &os) const {
    switch (getKind()) {
    case None:
      os << "none\n";
      return;
    case ApplySite:
      os << "apply site: " << *getFullApplySite();
      return;
    case CopyAddr:
      os << "copy_addr: " << *getCopyAddr();
      return;
    case Store:
      os << "store: " << *getStore();
      return;
    case Value:
      os << "value: " << *getValue();
      break;
    case ReturnTerm:
      os << "return term: " << *getReturnTerm()->getUser();
    }
  }

  SWIFT_DEBUG_DUMP { print(llvm::dbgs()); }
};

InOutSendingReturnedDiagnosticEmitter::LastValueEnum
InOutSendingReturnedDiagnosticEmitter::LastValueEnum::get(
    SILInstruction *user) {
  if (auto *cai = dyn_cast<CopyAddrInst>(user)) {
    return {cai};
  }

  if (auto *si = dyn_cast<StoreInst>(user)) {
    return {si};
  }

  if (auto fas = FullApplySite::isa(user)) {
    return {fas};
  }

  return {};
}

InOutSendingReturnedDiagnosticEmitter::LastValueEnum
InOutSendingReturnedDiagnosticEmitter::LastValueEnum::get(Operand *use) {
  if (auto value = get(use->getUser()))
    return value;

  if (auto *ti = dyn_cast<TermInst>(use->getUser())) {
    if (ti->getLoc().getKind() == SILLocation::ReturnKind) {
      return {use};
    }
  }

  return {};
}

bool InOutSendingReturnedDiagnosticEmitter::LastValueEnum::isSupported(
    Operand *use) {
  if (auto fas = FullApplySite::isa(use->getUser())) {
    if (fas.isIndirectResultOperand(*use)) {
      auto *fn = fas.getCalleeFunction();
      return fn && fn->getDeclRef();
    }
  }

  if (auto *ti = dyn_cast<TermInst>(use->getUser())) {
    if (ti->getLoc().getKind() == SILLocation::ReturnKind) {
      return true;
    }
  }

  return isa<CopyAddrInst, StoreInst>(use->getUser());
}

InOutSendingReturnedDiagnosticEmitter::LastValueEnum
InOutSendingReturnedDiagnosticEmitter::LastValueEnum::get(SILValue value) {
  if (auto *inst = value->getDefiningInstruction()) {
    if (auto e = get(inst))
      return e;
  }

  return {value};
}

void InOutSendingReturnedDiagnosticEmitter::emitLastValueEnum(
    const LastValueEnum &value, SILDynamicMergedIsolationInfo isolationInfo,
    SILLocation loc) {
  switch (value.getKind()) {
  case LastValueEnum::None:
    llvm::report_fatal_error("Found .none enum elt");
  case LastValueEnum::ApplySite:
    emitDeclRefError(value.getDeclRef(), isolationInfo,
                     loc ? loc : value.getLoc());
    return;
  case LastValueEnum::Store:
  case LastValueEnum::CopyAddr:
    emitValueError(value.getValue(), isolationInfo, loc ? loc : value.getLoc());
    return;
  case LastValueEnum::Value:
    emitValueError(value.getValue(), isolationInfo,
                   loc ? loc : functionExitingInst->getLoc());
    return;
  case LastValueEnum::ReturnTerm:
    emitValueError(value.getValue(), isolationInfo, loc ? loc : value.getLoc());
    return;
  }
  llvm::report_fatal_error("Should never hit this");
}

bool InOutSendingReturnedDiagnosticEmitter::emitOutParamIncomingValueError(
    const LastValueEnum &finalValue) {
  auto *block = finalValue.getParentBlock();
  auto state = raFuncInfo->getBlockState(block);
  assert(state.isNonNull());

  // Grab the exit partition of the block. We make a copy here on purpose
  // since it /is/ possible for DiagnosticEvaluator to modify
  auto workingExitPartition = state.get()->getExitPartition();

  // See if given the exit partition of the block if we would emit an error
  // when we execute an InOutSendingAtFunctionExit partition op.
  SmallFrozenMultiMap<Operand *, RequireInst, 8> sendingOpToRequireInstMultiMap;
  SmallVector<PartitionOpError, 2> errors;
  DiagnosticEvaluator evaluator(workingExitPartition, raFuncInfo,
                                sendingOpToRequireInstMultiMap, errors,
                                raFuncInfo->getSendingOperandToStateMap());
  PartitionOp op = PartitionOp::InOutSendingAtFunctionExit(
      inoutSendingParamElement, finalValue.getDefiningInsertionPoint());
  evaluator.apply(op);

  // Check if we got an error. If we did not, then this is not one of the
  // guilty code paths. Continue.
  if (errors.empty()) {
    return false;
  }

  // Loop through the errors to find our InOutReturnedError. We emit one error
  // per return... but we emit for multiple returns separate diagnostics.
  while (!errors.empty()) {
    auto err = errors.pop_back_val();
    if (err.getKind() != PartitionOpError::InOutSendingReturned)
      continue;
    auto castError = std::move(err).getInOutSendingReturnedError();
    if (castError.inoutSendingElement != inoutSendingParamElement)
      continue;
    // Ok, we found an error. Lets emit it and return early.
    if (finalValue == inoutSendingParam) {
      emitReturnInOutSendingError(isolationInfo, finalValue.getLoc());
      return true;
    }

    // Force us to use the location of the finalValue. We do not want to use the
    // function exiting inst.
    emitLastValueEnum(finalValue, isolationInfo, finalValue.getLoc());
    return true;
  }

  return false;
}

void InOutSendingReturnedDiagnosticEmitter::emit() {
  // Check if we had a separate erroring value that is our returned value. If we
  // do not then we just returned the 'inout sending' parameter. Emit a special
  // message and return.
  if (inoutSendingParam == returnedValue) {
    return emitReturnInOutSendingError(isolationInfo,
                                       functionExitingInst->getLoc());
  }

  // Before we do anything, see if we have a phi argument that is an epilogue
  // phi. In such a case, we want to process the incoming values.
  if (auto *phi = dyn_cast<SILPhiArgument>(returnedValue)) {
    bool handledValue = false;
    phi->visitIncomingPhiOperands([&](Operand *op) {
      if (op->getUser()->getLoc().getKind() != SILLocation::ReturnKind)
        return true;
      handledValue |=
          emitOutParamIncomingValueError(LastValueEnum::get(op->get()));
      return true;
    });
    if (handledValue)
      return;
  }

  // Check if we have an indirect out parameter as our erroring returned value.
  auto *fArg = dyn_cast<SILFunctionArgument>(returnedValue);
  if (!fArg || !fArg->isIndirectResult()) {
    // If we do not have one... emit a normal error.
    return emitLastValueEnum(LastValueEnum::get(returnedValue), isolationInfo);
  }

  SmallVector<LastValueEnum, 8> finalValues;
  if (!LastValueEnum::findLastValuesForOutParam(fArg, finalValues))
    return emitLastValueEnum(LastValueEnum::get(returnedValue), isolationInfo);

  // If we have a single value, then we have found our value.
  if (finalValues.size() == 1) {
    if (finalValues[0] == inoutSendingParam) {
      return emitReturnInOutSendingError(isolationInfo,
                                         finalValues[0].getLoc());
    }
    emitLastValueEnum(finalValues[0], isolationInfo);
    return;
  }

  // If we have multiple finalValues, then that means that we had multiple
  // return values. In such a case, we must have a single epilog block
  // that our finalValues jointly dominate. That means that we need to
  // determine which block the error actually occured along and emit an
  // error for the value in that block. We know we are going to emit an
  // error, so we can spend more time finding the better diagnostic since
  // we are going to fail.
  for (auto finalValue : finalValues) {
    emitOutParamIncomingValueError(finalValue);
  }
}

bool InOutSendingReturnedDiagnosticEmitter::LastValueEnum::
    findLastValuesForOutParam(SILFunctionArgument *fArg,
                              SmallVectorImpl<LastValueEnum> &lastValues) {
  assert(fArg->isIndirectResult());
  SmallVector<SILBasicBlock *, 8> visitedBlocks;
  SSAPrunedLiveness prunedLiveRange(fArg->getFunction(), &visitedBlocks);

  // Look for copy_addr and store uses into fArg. They should all be complete
  // stores.
  prunedLiveRange.initializeDef(fArg);
  for (auto *use : fArg->getUses()) {
    if (LastValueEnum::isSupported(use)) {
      prunedLiveRange.updateForUse(use->getUser(), false /*lifetime ending*/);
      continue;
    }
    return false;
  }

  PrunedLivenessBoundary boundary;
  prunedLiveRange.computeBoundary(boundary);

  for (auto *user : boundary.lastUsers) {
    if (auto e = LastValueEnum::get(user)) {
      lastValues.emplace_back(e);
      continue;
    }

    llvm::report_fatal_error("Out of sync with earlier check");
  }

  return true;
}

//===----------------------------------------------------------------------===//
//              MARK: InOutSendingNotDisconnected Error Emitter
//===----------------------------------------------------------------------===//

namespace {

class InOutSendingNotDisconnectedDiagnosticEmitter {
  /// The function exiting inst where the 'inout sending' parameter was actor
  /// isolated.
  TermInst *functionExitingInst;

  /// The 'inout sending' param that we are emitting an error for.
  SILValue inoutSendingParam;

  /// The dynamic actor isolated region info of our 'inout sending' value's
  /// region at the terminator inst.
  SILDynamicMergedIsolationInfo actorIsolatedRegionInfo;

  bool emittedErrorDiagnostic = false;

public:
  InOutSendingNotDisconnectedDiagnosticEmitter(
      TermInst *functionExitingInst, SILValue inoutSendingParam,
      SILDynamicMergedIsolationInfo actorIsolatedRegionInfo)
      : functionExitingInst(functionExitingInst),
        inoutSendingParam(inoutSendingParam),
        actorIsolatedRegionInfo(actorIsolatedRegionInfo) {}

  ~InOutSendingNotDisconnectedDiagnosticEmitter() {
    // If we were supposed to emit a diagnostic and didn't emit an unknown
    // pattern error.
    if (!emittedErrorDiagnostic)
      emitUnknownPatternError();
  }

  SILFunction *getFunction() const { return inoutSendingParam->getFunction(); }

  std::optional<DiagnosticBehavior> getBehaviorLimit() const {
    return inoutSendingParam->getType().getConcurrencyDiagnosticBehavior(
        getFunction());
  }

  void emitUnknownPatternError() {
    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(functionExitingInst,
                  diag::regionbasedisolation_unknown_pattern)
        .limitBehaviorIf(getBehaviorLimit());
  }

  void emit();

  ASTContext &getASTContext() const {
    return functionExitingInst->getFunction()->getASTContext();
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SourceLoc loc, Diag<T...> diag,
                                   U &&...args) {
    emittedErrorDiagnostic = true;
    return std::move(getASTContext()
                         .Diags.diagnose(loc, diag, std::forward<U>(args)...)
                         .warnUntilSwiftVersion(6));
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILLocation loc, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILInstruction *inst, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SourceLoc loc, Diag<T...> diag, U &&...args) {
    return getASTContext().Diags.diagnose(loc, diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILLocation loc, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILInstruction *inst, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(inst->getLoc(), diag, std::forward<U>(args)...);
  }
};

} // namespace

void InOutSendingNotDisconnectedDiagnosticEmitter::emit() {
  // We should always be able to find a name for an inout sending param. If we
  // do not, emit an unknown pattern error.
  auto varName = inferNameHelper(inoutSendingParam);
  if (!varName) {
    return emitUnknownPatternError();
  }

  // Then emit the note with greater context.
  auto descriptiveKindStr =
      actorIsolatedRegionInfo.printForDiagnostics(getFunction());

  diagnoseError(
      functionExitingInst,
      diag::regionbasedisolation_inout_sending_cannot_be_actor_isolated,
      *varName, descriptiveKindStr)
      .limitBehaviorIf(getBehaviorLimit());

  diagnoseNote(
      functionExitingInst,
      diag::regionbasedisolation_inout_sending_cannot_be_actor_isolated_note,
      *varName, descriptiveKindStr);
}

//===----------------------------------------------------------------------===//
//           MARK: AssignIsolatedIntoSendingResultDiagnosticEmitter
//===----------------------------------------------------------------------===//

namespace {

class AssignIsolatedIntoSendingResultDiagnosticEmitter {
  /// The use that actually caused the send.
  Operand *srcOperand;

  /// The specific out sending result.
  SILFunctionArgument *outSendingResult;

  /// The never-sent value that is in the same region as \p
  /// outSendingResult.
  SILValue neverSentValue;

  /// The region info that describes the dynamic dataflow derived isolation
  /// region info for the never-sent value.
  ///
  /// This is equal to the merge of the IsolationRegionInfo from all elements in
  /// the never-sent value's region when the error was diagnosed.
  SILDynamicMergedIsolationInfo isolatedValueIsolationRegionInfo;

  bool emittedErrorDiagnostic = false;

public:
  AssignIsolatedIntoSendingResultDiagnosticEmitter(
      Operand *srcOperand, SILFunctionArgument *outSendingResult,
      SILValue neverSentValue,
      SILDynamicMergedIsolationInfo isolatedValueIsolationRegionInfo)
      : srcOperand(srcOperand), outSendingResult(outSendingResult),
        neverSentValue(neverSentValue),
        isolatedValueIsolationRegionInfo(isolatedValueIsolationRegionInfo) {}

  ~AssignIsolatedIntoSendingResultDiagnosticEmitter() {
    // If we were supposed to emit a diagnostic and didn't emit an unknown
    // pattern error.
    if (!emittedErrorDiagnostic)
      emitUnknownPatternError();
  }

  SILFunction *getFunction() const { return srcOperand->getFunction(); }

  std::optional<DiagnosticBehavior> getConcurrencyDiagnosticBehavior() const {
    return outSendingResult->getType().getConcurrencyDiagnosticBehavior(
        getFunction());
  }

  void emitUnknownPatternError() {
    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(srcOperand->getUser(),
                  diag::regionbasedisolation_unknown_pattern)
        .limitBehaviorIf(getConcurrencyDiagnosticBehavior());
  }

  void emit();

  ASTContext &getASTContext() const {
    return srcOperand->getFunction()->getASTContext();
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SourceLoc loc, Diag<T...> diag,
                                   U &&...args) {
    emittedErrorDiagnostic = true;
    return std::move(getASTContext()
                         .Diags.diagnose(loc, diag, std::forward<U>(args)...)
                         .warnUntilSwiftVersion(6));
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILLocation loc, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILInstruction *inst, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(Operand *op, Diag<T...> diag, U &&...args) {
    return diagnoseError(op->getUser()->getLoc(), diag,
                         std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SourceLoc loc, Diag<T...> diag, U &&...args) {
    return getASTContext().Diags.diagnose(loc, diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILLocation loc, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILInstruction *inst, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(Operand *op, Diag<T...> diag, U &&...args) {
    return diagnoseNote(op->getUser()->getLoc(), diag,
                        std::forward<U>(args)...);
  }
};

} // namespace

/// Look through values looking for our out parameter. We want to tightly
/// control this to be conservative... so we handroll this.
static SILValue findOutParameter(SILValue v) {
  while (true) {
    SILValue temp = v;
    if (auto *initOpt = dyn_cast<InitEnumDataAddrInst>(temp)) {
      if (initOpt->getElement()->getParentEnum() ==
          initOpt->getFunction()->getASTContext().getOptionalDecl()) {
        temp = initOpt->getOperand();
      }
    }

    if (temp == v) {
      return v;
    }

    v = temp;
  }
}

void AssignIsolatedIntoSendingResultDiagnosticEmitter::emit() {
  // Then emit the note with greater context.
  auto descriptiveKindStr =
      isolatedValueIsolationRegionInfo.printForDiagnostics(getFunction());

  // Grab the var name if we can find it.
  if (auto varName = VariableNameInferrer::inferName(srcOperand->get())) {
    // In general, when we do an assignment like this, we assume that srcOperand
    // and our outSendingResult have the same type. This doesn't always happen
    // though especially if our outSendingResult is used as an out parameter of
    // a class_method. Check for such a case and if so, add to the end of our
    // string a path component for that class_method.
    if (srcOperand->get()->getType() != outSendingResult->getType()) {
      if (auto fas = FullApplySite::isa(srcOperand->getUser())) {
        if (fas.hasSelfArgument() &&
            fas.getSelfArgument() == srcOperand->get() &&
            fas.getNumIndirectSILResults() == 1) {
          // First check if our function argument is exactly our out parameter.
          bool canEmit = outSendingResult == fas.getIndirectSILResults()[0];

          // If that fails, see if we are storing into a temporary
          // alloc_stack. In such a case, find the root value that the temporary
          // is initialized to and see if that is our target function
          // argument. In such a case, we also want to add the decl name to our
          // type.
          if (!canEmit) {
            canEmit = outSendingResult ==
                      findOutParameter(fas.getIndirectSILResults()[0]);
          }

          if (canEmit) {
            if (auto *callee =
                    dyn_cast_or_null<MethodInst>(fas.getCalleeOrigin())) {
              SmallString<64> resultingString;
              resultingString.append(varName->str());
              resultingString += '.';
              resultingString += VariableNameInferrer::getNameFromDecl(
                  callee->getMember().getDecl());
              varName = fas->getFunction()->getASTContext().getIdentifier(
                  resultingString);
            }
          }
        }
      }
    }

    diagnoseError(
        srcOperand,
        diag::regionbasedisolation_out_sending_cannot_be_actor_isolated_named,
        *varName, descriptiveKindStr)
        .limitBehaviorIf(getConcurrencyDiagnosticBehavior());

    diagnoseNote(
        srcOperand,
        diag::
            regionbasedisolation_out_sending_cannot_be_actor_isolated_note_named,
        *varName, descriptiveKindStr);
    return;
  }

  Type type = neverSentValue->getType().getASTType();

  diagnoseError(
      srcOperand,
      diag::regionbasedisolation_out_sending_cannot_be_actor_isolated_type,
      type, descriptiveKindStr)
      .limitBehaviorIf(getConcurrencyDiagnosticBehavior());

  diagnoseNote(
      srcOperand,
      diag::regionbasedisolation_out_sending_cannot_be_actor_isolated_note_type,
      type, descriptiveKindStr);
  diagnoseNote(srcOperand, diag::regionbasedisolation_type_is_non_sendable,
               type);
}

//===----------------------------------------------------------------------===//
//              MARK: NonSendableIsolationCrossingResult Emitter
//===----------------------------------------------------------------------===//

/// Add Fix-It text for the given nominal type to adopt Sendable.
static void addSendableFixIt(const NominalTypeDecl *nominal,
                             InFlightDiagnostic &diag, bool unchecked) {
  if (nominal->getInherited().empty()) {
    SourceLoc fixItLoc = nominal->getBraces().Start;
    diag.fixItInsert(fixItLoc,
                     unchecked ? ": @unchecked Sendable" : ": Sendable");
  } else {
    auto fixItLoc = nominal->getInherited().getEndLoc();
    diag.fixItInsertAfter(fixItLoc,
                          unchecked ? ", @unchecked Sendable" : ", Sendable");
  }
}

/// Add Fix-It text for the given generic param declaration type to adopt
/// Sendable.
static void addSendableFixIt(const GenericTypeParamDecl *genericArgument,
                             InFlightDiagnostic &diag) {
  if (genericArgument->getInherited().empty()) {
    auto fixItLoc = genericArgument->getLoc();
    diag.fixItInsertAfter(fixItLoc, ": Sendable");
  } else {
    auto fixItLoc = genericArgument->getInherited().getEndLoc();
    diag.fixItInsertAfter(fixItLoc, " & Sendable");
  }
}

namespace {

struct NonSendableIsolationCrossingResultDiagnosticEmitter {
  RegionAnalysisValueMap &valueMap;

  using Error = PartitionOpError::NonSendableIsolationCrossingResultError;
  Error error;

  bool emittedErrorDiagnostic = false;

  /// The value assigned as the equivalence class representative. It is
  /// guaranteed to be from the isolation crossing function since we never treat
  /// isolation crossing functions as being look through.
  SILValue representative;

  NonSendableIsolationCrossingResultDiagnosticEmitter(
      RegionAnalysisValueMap &valueMap, Error &&error)
      : valueMap(valueMap), error(std::move(error)),
        representative(valueMap.getRepresentative(error.returnValueElement)) {}

  SILFunction *getFunction() const {
    return error.op->getSourceInst()->getFunction();
  }

  void emit();

  ASTContext &getASTContext() const {
    return error.op->getSourceInst()->getFunction()->getASTContext();
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SourceLoc loc, Diag<T...> diag,
                                   U &&...args) {
    emittedErrorDiagnostic = true;
    return std::move(getASTContext()
                         .Diags.diagnose(loc, diag, std::forward<U>(args)...)
                         .warnUntilSwiftVersion(6));
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILLocation loc, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseError(SILInstruction *inst, Diag<T...> diag,
                                   U &&...args) {
    return diagnoseError(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SourceLoc loc, Diag<T...> diag, U &&...args) {
    return getASTContext().Diags.diagnose(loc, diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILLocation loc, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(loc.getSourceLoc(), diag, std::forward<U>(args)...);
  }

  template <typename... T, typename... U>
  InFlightDiagnostic diagnoseNote(SILInstruction *inst, Diag<T...> diag,
                                  U &&...args) {
    return diagnoseNote(inst->getLoc(), diag, std::forward<U>(args)...);
  }

  std::optional<DiagnosticBehavior> getBehaviorLimit() const {
    return representative->getType().getConcurrencyDiagnosticBehavior(
        representative->getFunction());
  }

  void emitUnknownPatternError() {
    if (shouldAbortOnUnknownPatternMatchError()) {
      llvm::report_fatal_error(
          "RegionIsolation: Aborting on unknown pattern match error");
    }

    diagnoseError(error.op->getSourceInst(),
                  diag::regionbasedisolation_unknown_pattern)
        .limitBehaviorIf(getBehaviorLimit());
  }

  Type getType() const {
    if (auto *applyExpr =
            error.op->getSourceInst()->getLoc().getAsASTNode<ApplyExpr>()) {
      return applyExpr->getType();
    }

    // If we do not have an ApplyExpr, see if we can just infer the type from
    // the SILFunction type. This is only used in SIL test cases.
    if (auto fas = FullApplySite::isa(error.op->getSourceInst())) {
      return fas.getSubstCalleeType()
          ->getAllResultsSubstType(fas.getModule(),
                                   fas.getFunction()->getTypeExpansionContext())
          .getASTType();
    }

    return Type();
  }

  const ValueDecl *getCalledDecl() const {
    if (auto *applyExpr =
            error.op->getSourceInst()->getLoc().getAsASTNode<ApplyExpr>()) {
      if (auto calledValue =
              applyExpr->getCalledValue(true /*look through conversions*/)) {
        return calledValue;
      }
    }

    return nullptr;
  }

  std::optional<ApplyIsolationCrossing> getIsolationCrossing() const {
    if (auto *applyExpr =
            error.op->getSourceInst()->getLoc().getAsASTNode<ApplyExpr>()) {
      if (auto isolationCrossing = applyExpr->getIsolationCrossing()) {
        return *isolationCrossing;
      }
    }

    // If we have a SIL based test case, just return the actual isolation
    // crossing.
    if (auto fas = FullApplySite::isa(error.op->getSourceInst())) {
      if (auto isolationCrossing = fas.getIsolationCrossing())
        return *isolationCrossing;
    }

    return {};
  }
};

} // namespace

void NonSendableIsolationCrossingResultDiagnosticEmitter::emit() {
  auto isolationCrossing = getIsolationCrossing();
  if (!isolationCrossing)
    return emitUnknownPatternError();

  auto calleeIsolationStr = SILIsolationInfo::printActorIsolationForDiagnostics(
      getFunction(), isolationCrossing->getCalleeIsolation());
  auto callerIsolationStr = SILIsolationInfo::printActorIsolationForDiagnostics(
      getFunction(), isolationCrossing->getCallerIsolation());

  auto type = getType();
  if (getCalledDecl()) {
    diagnoseError(error.op->getSourceInst(),
                  diag::rbi_isolation_crossing_result, type, calleeIsolationStr,
                  getCalledDecl(), callerIsolationStr)
        .limitBehaviorIf(getBehaviorLimit());
  } else {
    diagnoseError(error.op->getSourceInst(),
                  diag::rbi_isolation_crossing_result_no_decl, type,
                  calleeIsolationStr, callerIsolationStr)
        .limitBehaviorIf(getBehaviorLimit());
  }
  if (type->is<FunctionType>()) {
    diagnoseNote(error.op->getSourceInst(),
                 diag::rbi_nonsendable_function_type);
    return;
  }

  auto *moduleDecl = error.op->getSourceInst()->getModule().getSwiftModule();
  if (auto *nominal = type->getNominalOrBoundGenericNominal()) {
    // If the nominal type is in the current module, suggest adding `Sendable`
    // if it makes sense.
    if (nominal->getParentModule() == moduleDecl &&
        (isa<StructDecl>(nominal) || isa<EnumDecl>(nominal))) {
      auto note = nominal->diagnose(diag::rbi_add_nominal_sendable_conformance,
                                    nominal);
      addSendableFixIt(nominal, note, /*unchecked*/ false);
    } else {
      nominal->diagnose(diag::rbi_non_sendable_nominal, nominal);
    }
    return;
  }

  if (auto genericArchetype = type->getAs<ArchetypeType>()) {
    auto interfaceType = genericArchetype->getInterfaceType();
    if (auto genericParamType = interfaceType->getAs<GenericTypeParamType>()) {
      auto *genericParamTypeDecl = genericParamType->getDecl();
      if (genericParamTypeDecl &&
          genericParamTypeDecl->getModuleContext() == moduleDecl) {
        auto diag = genericParamTypeDecl->diagnose(
            diag::rbi_add_generic_parameter_sendable_conformance, type);
        addSendableFixIt(genericParamTypeDecl, diag);
        return;
      }
    }
  }
}

//===----------------------------------------------------------------------===//
//                         MARK: Top Level Entrypoint
//===----------------------------------------------------------------------===//

void SendNonSendableImpl::emitVerbatimErrors() {
  for (auto &erasedError : foundVerbatimErrors) {
    switch (erasedError.getKind()) {
    case PartitionOpError::UnknownCodePattern:
    case PartitionOpError::LocalUseAfterSend:
    case PartitionOpError::InOutSendingNotInitializedAtExit:
      llvm_unreachable("Handled elsewhere");
    case PartitionOpError::AssignNeverSendableIntoSendingResult: {
      auto error =
          std::move(erasedError).getAssignNeverSendableIntoSendingResultError();
      REGIONBASEDISOLATION_LOG(error.print(llvm::dbgs(), info->getValueMap()));
      AssignIsolatedIntoSendingResultDiagnosticEmitter emitter(
          error.op->getSourceOp(), error.destValue, error.srcValue,
          error.srcIsolationRegionInfo);
      emitter.emit();
      continue;
    }
    case PartitionOpError::InOutSendingNotDisconnectedAtExit: {
      auto error =
          std::move(erasedError).getInOutSendingNotDisconnectedAtExitError();
      auto inoutSendingVal =
          info->getValueMap().getRepresentative(error.inoutSendingElement);
      auto isolationRegionInfo = error.isolationInfo;

      REGIONBASEDISOLATION_LOG(error.print(llvm::dbgs(), info->getValueMap()));

      InOutSendingNotDisconnectedDiagnosticEmitter emitter(
          cast<TermInst>(error.op->getSourceInst()), inoutSendingVal,
          isolationRegionInfo);
      emitter.emit();
      continue;
    }
    case PartitionOpError::InOutSendingReturned: {
      auto error = std::move(erasedError).getInOutSendingReturnedError();
      auto inoutSendingVal =
          info->getValueMap().getRepresentative(error.inoutSendingElement);
      auto returnedValue =
          info->getValueMap().getRepresentative(error.returnedValue);

      REGIONBASEDISOLATION_LOG(error.print(llvm::dbgs(), info->getValueMap()));

      InOutSendingReturnedDiagnosticEmitter emitter(
          info, cast<TermInst>(error.op->getSourceInst()), inoutSendingVal,
          error.inoutSendingElement, returnedValue, error.isolationInfo);
      emitter.emit();
      continue;
    }
    case PartitionOpError::SentNeverSendable: {
      auto e = std::move(erasedError).getSentNeverSendableError();
      REGIONBASEDISOLATION_LOG(e.print(llvm::dbgs(), info->getValueMap()));
      SentNeverSendableDiagnosticInferrer diagnosticInferrer(
          info->getValueMap(), std::move(e));
      diagnosticInferrer.run();
      continue;
    }
    case PartitionOpError::NonSendableIsolationCrossingResult: {
      auto e =
          std::move(erasedError).getNonSendableIsolationCrossingResultError();
      REGIONBASEDISOLATION_LOG(e.print(llvm::dbgs(), info->getValueMap()));
      NonSendableIsolationCrossingResultDiagnosticEmitter diagnosticInferrer(
          info->getValueMap(), std::move(e));
      diagnosticInferrer.emit();
      continue;
    }
    }
    llvm_unreachable("Covered switch isn't covered?!");
  }
}

/// Once we have reached a fixpoint, this routine runs over all blocks again
/// reporting any failures by applying our ops to the converged dataflow
/// state.
void SendNonSendableImpl::emitDiagnostics() {
  auto *function = info->getFunction();
  REGIONBASEDISOLATION_LOG(llvm::dbgs() << "Emitting diagnostics for function "
                                        << function->getName() << "\n");

  runDiagnosticEvaluator();
  emitUseAfterSendDiagnostics();
  emitVerbatimErrors();
}

namespace {

class SendNonSendable : public SILFunctionTransform {
  void run() override {
    SILFunction *function = getFunction();

    auto *functionInfo = getAnalysis<RegionAnalysis>()->get(function);
    if (!functionInfo->isSupportedFunction()) {
      REGIONBASEDISOLATION_LOG(llvm::dbgs()
                               << "===> SKIPPING UNSUPPORTED FUNCTION: "
                               << function->getName() << '\n');

      return;
    }

    REGIONBASEDISOLATION_LOG(
        llvm::dbgs() << "===> PROCESSING: " << function->getName() << '\n');

    SendNonSendableImpl impl(functionInfo);
    impl.emitDiagnostics();
  }
};

} // end anonymous namespace

SILTransform *swift::createSendNonSendable() { return new SendNonSendable(); }