llvm-project/clang-tools-extra/clangd/InlayHints.cpp

//===--- InlayHints.cpp ------------------------------------------*- C++-*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "InlayHints.h"
#include "AST.h"
#include "Config.h"
#include "HeuristicResolver.h"
#include "ParsedAST.h"
#include "SourceCode.h"
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/Type.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/SourceManager.h"
#include "llvm/ADT/ScopeExit.h"
#include <optional>

namespace clang {
namespace clangd {
namespace {

// For now, inlay hints are always anchored at the left or right of their range.
enum class HintSide { Left, Right };

// Helper class to iterate over the designator names of an aggregate type.
//
// For an array type, yields [0], [1], [2]...
// For aggregate classes, yields null for each base, then .field1, .field2, ...
class AggregateDesignatorNames {
public:
  AggregateDesignatorNames(QualType T) {
    if (!T.isNull()) {
      T = T.getCanonicalType();
      if (T->isArrayType()) {
        IsArray = true;
        Valid = true;
        return;
      }
      if (const RecordDecl *RD = T->getAsRecordDecl()) {
        Valid = true;
        FieldsIt = RD->field_begin();
        FieldsEnd = RD->field_end();
        if (const auto *CRD = llvm::dyn_cast<CXXRecordDecl>(RD)) {
          BasesIt = CRD->bases_begin();
          BasesEnd = CRD->bases_end();
          Valid = CRD->isAggregate();
        }
        OneField = Valid && BasesIt == BasesEnd && FieldsIt != FieldsEnd &&
                   std::next(FieldsIt) == FieldsEnd;
      }
    }
  }
  // Returns false if the type was not an aggregate.
  operator bool() { return Valid; }
  // Advance to the next element in the aggregate.
  void next() {
    if (IsArray)
      ++Index;
    else if (BasesIt != BasesEnd)
      ++BasesIt;
    else if (FieldsIt != FieldsEnd)
      ++FieldsIt;
  }
  // Print the designator to Out.
  // Returns false if we could not produce a designator for this element.
  bool append(std::string &Out, bool ForSubobject) {
    if (IsArray) {
      Out.push_back('[');
      Out.append(std::to_string(Index));
      Out.push_back(']');
      return true;
    }
    if (BasesIt != BasesEnd)
      return false; // Bases can't be designated. Should we make one up?
    if (FieldsIt != FieldsEnd) {
      llvm::StringRef FieldName;
      if (const IdentifierInfo *II = FieldsIt->getIdentifier())
        FieldName = II->getName();

      // For certain objects, their subobjects may be named directly.
      if (ForSubobject &&
          (FieldsIt->isAnonymousStructOrUnion() ||
           // std::array<int,3> x = {1,2,3}. Designators not strictly valid!
           (OneField && isReservedName(FieldName))))
        return true;

      if (!FieldName.empty() && !isReservedName(FieldName)) {
        Out.push_back('.');
        Out.append(FieldName.begin(), FieldName.end());
        return true;
      }
      return false;
    }
    return false;
  }

private:
  bool Valid = false;
  bool IsArray = false;
  bool OneField = false; // e.g. std::array { T __elements[N]; }
  unsigned Index = 0;
  CXXRecordDecl::base_class_const_iterator BasesIt;
  CXXRecordDecl::base_class_const_iterator BasesEnd;
  RecordDecl::field_iterator FieldsIt;
  RecordDecl::field_iterator FieldsEnd;
};

// Collect designator labels describing the elements of an init list.
//
// This function contributes the designators of some (sub)object, which is
// represented by the semantic InitListExpr Sem.
// This includes any nested subobjects, but *only* if they are part of the same
// original syntactic init list (due to brace elision).
// In other words, it may descend into subobjects but not written init-lists.
//
// For example: struct Outer { Inner a,b; }; struct Inner { int x, y; }
//              Outer o{{1, 2}, 3};
// This function will be called with Sem = { {1, 2}, {3, ImplicitValue} }
// It should generate designators '.a:' and '.b.x:'.
// '.a:' is produced directly without recursing into the written sublist.
// (The written sublist will have a separate collectDesignators() call later).
// Recursion with Prefix='.b' and Sem = {3, ImplicitValue} produces '.b.x:'.
void collectDesignators(const InitListExpr *Sem,
                        llvm::DenseMap<SourceLocation, std::string> &Out,
                        const llvm::DenseSet<SourceLocation> &NestedBraces,
                        std::string &Prefix) {
  if (!Sem || Sem->isTransparent())
    return;
  assert(Sem->isSemanticForm());

  // The elements of the semantic form all correspond to direct subobjects of
  // the aggregate type. `Fields` iterates over these subobject names.
  AggregateDesignatorNames Fields(Sem->getType());
  if (!Fields)
    return;
  for (const Expr *Init : Sem->inits()) {
    auto Next = llvm::make_scope_exit([&, Size(Prefix.size())] {
      Fields.next();       // Always advance to the next subobject name.
      Prefix.resize(Size); // Erase any designator we appended.
    });
    // Skip for a broken initializer or if it is a "hole" in a subobject that
    // was not explicitly initialized.
    if (!Init || llvm::isa<ImplicitValueInitExpr>(Init))
      continue;

    const auto *BraceElidedSubobject = llvm::dyn_cast<InitListExpr>(Init);
    if (BraceElidedSubobject &&
        NestedBraces.contains(BraceElidedSubobject->getLBraceLoc()))
      BraceElidedSubobject = nullptr; // there were braces!

    if (!Fields.append(Prefix, BraceElidedSubobject != nullptr))
      continue; // no designator available for this subobject
    if (BraceElidedSubobject) {
      // If the braces were elided, this aggregate subobject is initialized
      // inline in the same syntactic list.
      // Descend into the semantic list describing the subobject.
      // (NestedBraces are still correct, they're from the same syntactic list).
      collectDesignators(BraceElidedSubobject, Out, NestedBraces, Prefix);
      continue;
    }
    Out.try_emplace(Init->getBeginLoc(), Prefix);
  }
}

// Get designators describing the elements of a (syntactic) init list.
// This does not produce designators for any explicitly-written nested lists.
llvm::DenseMap<SourceLocation, std::string>
getDesignators(const InitListExpr *Syn) {
  assert(Syn->isSyntacticForm());

  // collectDesignators needs to know which InitListExprs in the semantic tree
  // were actually written, but InitListExpr::isExplicit() lies.
  // Instead, record where braces of sub-init-lists occur in the syntactic form.
  llvm::DenseSet<SourceLocation> NestedBraces;
  for (const Expr *Init : Syn->inits())
    if (auto *Nested = llvm::dyn_cast<InitListExpr>(Init))
      NestedBraces.insert(Nested->getLBraceLoc());

  // Traverse the semantic form to find the designators.
  // We use their SourceLocation to correlate with the syntactic form later.
  llvm::DenseMap<SourceLocation, std::string> Designators;
  std::string EmptyPrefix;
  collectDesignators(Syn->isSemanticForm() ? Syn : Syn->getSemanticForm(),
                     Designators, NestedBraces, EmptyPrefix);
  return Designators;
}

// Determines if any intermediate type in desugaring QualType QT is of
// substituted template parameter type. Ignore pointer or reference wrappers.
bool isSugaredTemplateParameter(QualType QT) {
  static auto PeelWrappers = [](QualType QT) {
    // Neither `PointerType` nor `ReferenceType` is considered as sugared
    // type. Peel it.
    QualType Next;
    while (!(Next = QT->getPointeeType()).isNull())
      QT = Next;
    return QT;
  };
  while (true) {
    QualType Desugared =
        PeelWrappers(QT->getLocallyUnqualifiedSingleStepDesugaredType());
    if (Desugared == QT)
      break;
    if (Desugared->getAs<SubstTemplateTypeParmType>())
      return true;
    QT = Desugared;
  }
  return false;
}

// A simple wrapper for `clang::desugarForDiagnostic` that provides optional
// semantic.
std::optional<QualType> desugar(ASTContext &AST, QualType QT) {
  bool ShouldAKA = false;
  auto Desugared = clang::desugarForDiagnostic(AST, QT, ShouldAKA);
  if (!ShouldAKA)
    return std::nullopt;
  return Desugared;
}

// Apply a series of heuristic methods to determine whether or not a QualType QT
// is suitable for desugaring (e.g. getting the real name behind the using-alias
// name). If so, return the desugared type. Otherwise, return the unchanged
// parameter QT.
//
// This could be refined further. See
// https://github.com/clangd/clangd/issues/1298.
QualType maybeDesugar(ASTContext &AST, QualType QT) {
  // Prefer desugared type for name that aliases the template parameters.
  // This can prevent things like printing opaque `: type` when accessing std
  // containers.
  if (isSugaredTemplateParameter(QT))
    return desugar(AST, QT).value_or(QT);

  // Prefer desugared type for `decltype(expr)` specifiers.
  if (QT->isDecltypeType())
    return QT.getCanonicalType();
  if (const AutoType *AT = QT->getContainedAutoType())
    if (!AT->getDeducedType().isNull() &&
        AT->getDeducedType()->isDecltypeType())
      return QT.getCanonicalType();

  return QT;
}

class InlayHintVisitor : public RecursiveASTVisitor<InlayHintVisitor> {
public:
  InlayHintVisitor(std::vector<InlayHint> &Results, ParsedAST &AST,
                   const Config &Cfg, std::optional<Range> RestrictRange)
      : Results(Results), AST(AST.getASTContext()), Tokens(AST.getTokens()),
        Cfg(Cfg), RestrictRange(std::move(RestrictRange)),
        MainFileID(AST.getSourceManager().getMainFileID()),
        Resolver(AST.getHeuristicResolver()),
        TypeHintPolicy(this->AST.getPrintingPolicy()) {
    bool Invalid = false;
    llvm::StringRef Buf =
        AST.getSourceManager().getBufferData(MainFileID, &Invalid);
    MainFileBuf = Invalid ? StringRef{} : Buf;

    TypeHintPolicy.SuppressScope = true; // keep type names short
    TypeHintPolicy.AnonymousTagLocations =
        false; // do not print lambda locations

    // Not setting PrintCanonicalTypes for "auto" allows
    // SuppressDefaultTemplateArgs (set by default) to have an effect.
  }

  bool VisitTypeLoc(TypeLoc TL) {
    if (const auto *DT = llvm::dyn_cast<DecltypeType>(TL.getType()))
      if (QualType UT = DT->getUnderlyingType(); !UT->isDependentType())
        addTypeHint(TL.getSourceRange(), UT, ": ");
    return true;
  }

  bool VisitCXXConstructExpr(CXXConstructExpr *E) {
    // Weed out constructor calls that don't look like a function call with
    // an argument list, by checking the validity of getParenOrBraceRange().
    // Also weed out std::initializer_list constructors as there are no names
    // for the individual arguments.
    if (!E->getParenOrBraceRange().isValid() ||
        E->isStdInitListInitialization()) {
      return true;
    }

    processCall(E->getConstructor(), {E->getArgs(), E->getNumArgs()});
    return true;
  }

  bool VisitCallExpr(CallExpr *E) {
    if (!Cfg.InlayHints.Parameters)
      return true;

    // Do not show parameter hints for operator calls written using operator
    // syntax or user-defined literals. (Among other reasons, the resulting
    // hints can look awkard, e.g. the expression can itself be a function
    // argument and then we'd get two hints side by side).
    if (isa<CXXOperatorCallExpr>(E) || isa<UserDefinedLiteral>(E))
      return true;

    auto CalleeDecls = Resolver->resolveCalleeOfCallExpr(E);
    if (CalleeDecls.size() != 1)
      return true;
    const FunctionDecl *Callee = nullptr;
    if (const auto *FD = dyn_cast<FunctionDecl>(CalleeDecls[0]))
      Callee = FD;
    else if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(CalleeDecls[0]))
      Callee = FTD->getTemplatedDecl();
    if (!Callee)
      return true;

    processCall(Callee, {E->getArgs(), E->getNumArgs()});
    return true;
  }

  bool VisitFunctionDecl(FunctionDecl *D) {
    if (auto *FPT =
            llvm::dyn_cast<FunctionProtoType>(D->getType().getTypePtr())) {
      if (!FPT->hasTrailingReturn()) {
        if (auto FTL = D->getFunctionTypeLoc())
          addReturnTypeHint(D, FTL.getRParenLoc());
      }
    }
    if (Cfg.InlayHints.BlockEnd && D->isThisDeclarationADefinition()) {
      // We use `printName` here to properly print name of ctor/dtor/operator
      // overload.
      if (const Stmt *Body = D->getBody())
        addBlockEndHint(Body->getSourceRange(), "", printName(AST, *D), "");
    }
    return true;
  }

  bool VisitTagDecl(TagDecl *D) {
    if (Cfg.InlayHints.BlockEnd && D->isThisDeclarationADefinition()) {
      std::string DeclPrefix = D->getKindName().str();
      if (const auto *ED = dyn_cast<EnumDecl>(D)) {
        if (ED->isScoped())
          DeclPrefix += ED->isScopedUsingClassTag() ? " class" : " struct";
      };
      addBlockEndHint(D->getBraceRange(), DeclPrefix, getSimpleName(*D), ";");
    }
    return true;
  }

  bool VisitNamespaceDecl(NamespaceDecl *D) {
    if (Cfg.InlayHints.BlockEnd) {
      // For namespace, the range actually starts at the namespace keyword. But
      // it should be fine since it's usually very short.
      addBlockEndHint(D->getSourceRange(), "namespace", getSimpleName(*D), "");
    }
    return true;
  }

  bool VisitLambdaExpr(LambdaExpr *E) {
    FunctionDecl *D = E->getCallOperator();
    if (!E->hasExplicitResultType())
      addReturnTypeHint(D, E->hasExplicitParameters()
                               ? D->getFunctionTypeLoc().getRParenLoc()
                               : E->getIntroducerRange().getEnd());
    return true;
  }

  void addReturnTypeHint(FunctionDecl *D, SourceRange Range) {
    auto *AT = D->getReturnType()->getContainedAutoType();
    if (!AT || AT->getDeducedType().isNull())
      return;
    addTypeHint(Range, D->getReturnType(), /*Prefix=*/"-> ");
  }

  bool VisitVarDecl(VarDecl *D) {
    // Do not show hints for the aggregate in a structured binding,
    // but show hints for the individual bindings.
    if (auto *DD = dyn_cast<DecompositionDecl>(D)) {
      for (auto *Binding : DD->bindings()) {
        // For structured bindings, print canonical types. This is important
        // because for bindings that use the tuple_element protocol, the
        // non-canonical types would be "tuple_element<I, A>::type".
        if (auto Type = Binding->getType(); !Type.isNull())
          addTypeHint(Binding->getLocation(), Type.getCanonicalType(),
                      /*Prefix=*/": ");
      }
      return true;
    }

    if (auto *AT = D->getType()->getContainedAutoType()) {
      if (AT->isDeduced() && !D->getType()->isDependentType()) {
        // Our current approach is to place the hint on the variable
        // and accordingly print the full type
        // (e.g. for `const auto& x = 42`, print `const int&`).
        // Alternatively, we could place the hint on the `auto`
        // (and then just print the type deduced for the `auto`).
        addTypeHint(D->getLocation(), D->getType(), /*Prefix=*/": ");
      }
    }

    // Handle templates like `int foo(auto x)` with exactly one instantiation.
    if (auto *PVD = llvm::dyn_cast<ParmVarDecl>(D)) {
      if (D->getIdentifier() && PVD->getType()->isDependentType() &&
          !getContainedAutoParamType(D->getTypeSourceInfo()->getTypeLoc())
               .isNull()) {
        if (auto *IPVD = getOnlyParamInstantiation(PVD))
          addTypeHint(D->getLocation(), IPVD->getType(), /*Prefix=*/": ");
      }
    }

    return true;
  }

  ParmVarDecl *getOnlyParamInstantiation(ParmVarDecl *D) {
    auto *TemplateFunction = llvm::dyn_cast<FunctionDecl>(D->getDeclContext());
    if (!TemplateFunction)
      return nullptr;
    auto *InstantiatedFunction = llvm::dyn_cast_or_null<FunctionDecl>(
        getOnlyInstantiation(TemplateFunction));
    if (!InstantiatedFunction)
      return nullptr;

    unsigned ParamIdx = 0;
    for (auto *Param : TemplateFunction->parameters()) {
      // Can't reason about param indexes in the presence of preceding packs.
      // And if this param is a pack, it may expand to multiple params.
      if (Param->isParameterPack())
        return nullptr;
      if (Param == D)
        break;
      ++ParamIdx;
    }
    assert(ParamIdx < TemplateFunction->getNumParams() &&
           "Couldn't find param in list?");
    assert(ParamIdx < InstantiatedFunction->getNumParams() &&
           "Instantiated function has fewer (non-pack) parameters?");
    return InstantiatedFunction->getParamDecl(ParamIdx);
  }

  bool VisitInitListExpr(InitListExpr *Syn) {
    // We receive the syntactic form here (shouldVisitImplicitCode() is false).
    // This is the one we will ultimately attach designators to.
    // It may have subobject initializers inlined without braces. The *semantic*
    // form of the init-list has nested init-lists for these.
    // getDesignators will look at the semantic form to determine the labels.
    assert(Syn->isSyntacticForm() && "RAV should not visit implicit code!");
    if (!Cfg.InlayHints.Designators)
      return true;
    if (Syn->isIdiomaticZeroInitializer(AST.getLangOpts()))
      return true;
    llvm::DenseMap<SourceLocation, std::string> Designators =
        getDesignators(Syn);
    for (const Expr *Init : Syn->inits()) {
      if (llvm::isa<DesignatedInitExpr>(Init))
        continue;
      auto It = Designators.find(Init->getBeginLoc());
      if (It != Designators.end() &&
          !isPrecededByParamNameComment(Init, It->second))
        addDesignatorHint(Init->getSourceRange(), It->second);
    }
    return true;
  }

  // FIXME: Handle RecoveryExpr to try to hint some invalid calls.

private:
  using NameVec = SmallVector<StringRef, 8>;

  void processCall(const FunctionDecl *Callee,
                   llvm::ArrayRef<const Expr *> Args) {
    if (!Cfg.InlayHints.Parameters || Args.size() == 0 || !Callee)
      return;

    // The parameter name of a move or copy constructor is not very interesting.
    if (auto *Ctor = dyn_cast<CXXConstructorDecl>(Callee))
      if (Ctor->isCopyOrMoveConstructor())
        return;

    // Resolve parameter packs to their forwarded parameter
    auto ForwardedParams = resolveForwardingParameters(Callee);

    NameVec ParameterNames = chooseParameterNames(ForwardedParams);

    // Exclude setters (i.e. functions with one argument whose name begins with
    // "set"), and builtins like std::move/forward/... as their parameter name
    // is also not likely to be interesting.
    if (isSetter(Callee, ParameterNames) || isSimpleBuiltin(Callee))
      return;

    for (size_t I = 0; I < ParameterNames.size() && I < Args.size(); ++I) {
      // Pack expansion expressions cause the 1:1 mapping between arguments and
      // parameters to break down, so we don't add further inlay hints if we
      // encounter one.
      if (isa<PackExpansionExpr>(Args[I])) {
        break;
      }

      StringRef Name = ParameterNames[I];
      bool NameHint = shouldHintName(Args[I], Name);
      bool ReferenceHint =
          shouldHintReference(Callee->getParamDecl(I), ForwardedParams[I]);

      if (NameHint || ReferenceHint) {
        addInlayHint(Args[I]->getSourceRange(), HintSide::Left,
                     InlayHintKind::Parameter, ReferenceHint ? "&" : "",
                     NameHint ? Name : "", ": ");
      }
    }
  }

  static bool isSetter(const FunctionDecl *Callee, const NameVec &ParamNames) {
    if (ParamNames.size() != 1)
      return false;

    StringRef Name = getSimpleName(*Callee);
    if (!Name.starts_with_insensitive("set"))
      return false;

    // In addition to checking that the function has one parameter and its
    // name starts with "set", also check that the part after "set" matches
    // the name of the parameter (ignoring case). The idea here is that if
    // the parameter name differs, it may contain extra information that
    // may be useful to show in a hint, as in:
    //   void setTimeout(int timeoutMillis);
    // This currently doesn't handle cases where params use snake_case
    // and functions don't, e.g.
    //   void setExceptionHandler(EHFunc exception_handler);
    // We could improve this by replacing `equals_insensitive` with some
    // `sloppy_equals` which ignores case and also skips underscores.
    StringRef WhatItIsSetting = Name.substr(3).ltrim("_");
    return WhatItIsSetting.equals_insensitive(ParamNames[0]);
  }

  // Checks if the callee is one of the builtins
  // addressof, as_const, forward, move(_if_noexcept)
  static bool isSimpleBuiltin(const FunctionDecl *Callee) {
    switch (Callee->getBuiltinID()) {
    case Builtin::BIaddressof:
    case Builtin::BIas_const:
    case Builtin::BIforward:
    case Builtin::BImove:
    case Builtin::BImove_if_noexcept:
      return true;
    default:
      return false;
    }
  }

  bool shouldHintName(const Expr *Arg, StringRef ParamName) {
    if (ParamName.empty())
      return false;

    // If the argument expression is a single name and it matches the
    // parameter name exactly, omit the name hint.
    if (ParamName == getSpelledIdentifier(Arg))
      return false;

    // Exclude argument expressions preceded by a /*paramName*/.
    if (isPrecededByParamNameComment(Arg, ParamName))
      return false;

    return true;
  }

  bool shouldHintReference(const ParmVarDecl *Param,
                           const ParmVarDecl *ForwardedParam) {
    // We add a & hint only when the argument is passed as mutable reference.
    // For parameters that are not part of an expanded pack, this is
    // straightforward. For expanded pack parameters, it's likely that they will
    // be forwarded to another function. In this situation, we only want to add
    // the reference hint if the argument is actually being used via mutable
    // reference. This means we need to check
    // 1. whether the value category of the argument is preserved, i.e. each
    //    pack expansion uses std::forward correctly.
    // 2. whether the argument is ever copied/cast instead of passed
    //    by-reference
    // Instead of checking this explicitly, we use the following proxy:
    // 1. the value category can only change from rvalue to lvalue during
    //    forwarding, so checking whether both the parameter of the forwarding
    //    function and the forwarded function are lvalue references detects such
    //    a conversion.
    // 2. if the argument is copied/cast somewhere in the chain of forwarding
    //    calls, it can only be passed on to an rvalue reference or const lvalue
    //    reference parameter. Thus if the forwarded parameter is a mutable
    //    lvalue reference, it cannot have been copied/cast to on the way.
    // Additionally, we should not add a reference hint if the forwarded
    // parameter was only partially resolved, i.e. points to an expanded pack
    // parameter, since we do not know how it will be used eventually.
    auto Type = Param->getType();
    auto ForwardedType = ForwardedParam->getType();
    return Type->isLValueReferenceType() &&
           ForwardedType->isLValueReferenceType() &&
           !ForwardedType.getNonReferenceType().isConstQualified() &&
           !isExpandedFromParameterPack(ForwardedParam);
  }

  // Checks if "E" is spelled in the main file and preceded by a C-style comment
  // whose contents match ParamName (allowing for whitespace and an optional "="
  // at the end.
  bool isPrecededByParamNameComment(const Expr *E, StringRef ParamName) {
    auto &SM = AST.getSourceManager();
    auto FileLoc = SM.getFileLoc(E->getBeginLoc());
    auto Decomposed = SM.getDecomposedLoc(FileLoc);
    if (Decomposed.first != MainFileID)
      return false;

    StringRef SourcePrefix = MainFileBuf.substr(0, Decomposed.second);
    // Allow whitespace between comment and expression.
    SourcePrefix = SourcePrefix.rtrim();
    // Check for comment ending.
    if (!SourcePrefix.consume_back("*/"))
      return false;
    // Ignore some punctuation and whitespace around comment.
    // In particular this allows designators to match nicely.
    llvm::StringLiteral IgnoreChars = " =.";
    SourcePrefix = SourcePrefix.rtrim(IgnoreChars);
    ParamName = ParamName.trim(IgnoreChars);
    // Other than that, the comment must contain exactly ParamName.
    if (!SourcePrefix.consume_back(ParamName))
      return false;
    SourcePrefix = SourcePrefix.rtrim(IgnoreChars);
    return SourcePrefix.endswith("/*");
  }

  // If "E" spells a single unqualified identifier, return that name.
  // Otherwise, return an empty string.
  static StringRef getSpelledIdentifier(const Expr *E) {
    E = E->IgnoreUnlessSpelledInSource();

    if (auto *DRE = dyn_cast<DeclRefExpr>(E))
      if (!DRE->getQualifier())
        return getSimpleName(*DRE->getDecl());

    if (auto *ME = dyn_cast<MemberExpr>(E))
      if (!ME->getQualifier() && ME->isImplicitAccess())
        return getSimpleName(*ME->getMemberDecl());

    return {};
  }

  NameVec chooseParameterNames(SmallVector<const ParmVarDecl *> Parameters) {
    NameVec ParameterNames;
    for (const auto *P : Parameters) {
      if (isExpandedFromParameterPack(P)) {
        // If we haven't resolved a pack paramater (e.g. foo(Args... args)) to a
        // non-pack parameter, then hinting as foo(args: 1, args: 2, args: 3) is
        // unlikely to be useful.
        ParameterNames.emplace_back();
      } else {
        auto SimpleName = getSimpleName(*P);
        // If the parameter is unnamed in the declaration:
        // attempt to get its name from the definition
        if (SimpleName.empty()) {
          if (const auto *PD = getParamDefinition(P)) {
            SimpleName = getSimpleName(*PD);
          }
        }
        ParameterNames.emplace_back(SimpleName);
      }
    }

    // Standard library functions often have parameter names that start
    // with underscores, which makes the hints noisy, so strip them out.
    for (auto &Name : ParameterNames)
      stripLeadingUnderscores(Name);

    return ParameterNames;
  }

  // for a ParmVarDecl from a function declaration, returns the corresponding
  // ParmVarDecl from the definition if possible, nullptr otherwise.
  static const ParmVarDecl *getParamDefinition(const ParmVarDecl *P) {
    if (auto *Callee = dyn_cast<FunctionDecl>(P->getDeclContext())) {
      if (auto *Def = Callee->getDefinition()) {
        auto I = std::distance(Callee->param_begin(),
                               llvm::find(Callee->parameters(), P));
        if (I < Callee->getNumParams()) {
          return Def->getParamDecl(I);
        }
      }
    }
    return nullptr;
  }

  static void stripLeadingUnderscores(StringRef &Name) {
    Name = Name.ltrim('_');
  }

  static StringRef getSimpleName(const NamedDecl &D) {
    if (IdentifierInfo *Ident = D.getDeclName().getAsIdentifierInfo()) {
      return Ident->getName();
    }

    return StringRef();
  }

  // We pass HintSide rather than SourceLocation because we want to ensure
  // it is in the same file as the common file range.
  void addInlayHint(SourceRange R, HintSide Side, InlayHintKind Kind,
                    llvm::StringRef Prefix, llvm::StringRef Label,
                    llvm::StringRef Suffix) {
    auto LSPRange = getHintRange(R);
    if (!LSPRange)
      return;

    addInlayHint(*LSPRange, Side, Kind, Prefix, Label, Suffix);
  }

  void addInlayHint(Range LSPRange, HintSide Side, InlayHintKind Kind,
                    llvm::StringRef Prefix, llvm::StringRef Label,
                    llvm::StringRef Suffix) {
    // We shouldn't get as far as adding a hint if the category is disabled.
    // We'd like to disable as much of the analysis as possible above instead.
    // Assert in debug mode but add a dynamic check in production.
    assert(Cfg.InlayHints.Enabled && "Shouldn't get here if disabled!");
    switch (Kind) {
#define CHECK_KIND(Enumerator, ConfigProperty)                                 \
  case InlayHintKind::Enumerator:                                              \
    assert(Cfg.InlayHints.ConfigProperty &&                                    \
           "Shouldn't get here if kind is disabled!");                         \
    if (!Cfg.InlayHints.ConfigProperty)                                        \
      return;                                                                  \
    break
      CHECK_KIND(Parameter, Parameters);
      CHECK_KIND(Type, DeducedTypes);
      CHECK_KIND(Designator, Designators);
      CHECK_KIND(BlockEnd, BlockEnd);
#undef CHECK_KIND
    }

    Position LSPPos = Side == HintSide::Left ? LSPRange.start : LSPRange.end;
    if (RestrictRange &&
        (LSPPos < RestrictRange->start || !(LSPPos < RestrictRange->end)))
      return;
    bool PadLeft = Prefix.consume_front(" ");
    bool PadRight = Suffix.consume_back(" ");
    Results.push_back(InlayHint{LSPPos, (Prefix + Label + Suffix).str(), Kind,
                                PadLeft, PadRight, LSPRange});
  }

  // Get the range of the main file that *exactly* corresponds to R.
  std::optional<Range> getHintRange(SourceRange R) {
    const auto &SM = AST.getSourceManager();
    auto Spelled = Tokens.spelledForExpanded(Tokens.expandedTokens(R));
    // TokenBuffer will return null if e.g. R corresponds to only part of a
    // macro expansion.
    if (!Spelled || Spelled->empty())
      return std::nullopt;
    // Hint must be within the main file, not e.g. a non-preamble include.
    if (SM.getFileID(Spelled->front().location()) != SM.getMainFileID() ||
        SM.getFileID(Spelled->back().location()) != SM.getMainFileID())
      return std::nullopt;
    return Range{sourceLocToPosition(SM, Spelled->front().location()),
                 sourceLocToPosition(SM, Spelled->back().endLocation())};
  }

  void addTypeHint(SourceRange R, QualType T, llvm::StringRef Prefix) {
    if (!Cfg.InlayHints.DeducedTypes || T.isNull())
      return;

    // The sugared type is more useful in some cases, and the canonical
    // type in other cases.
    auto Desugared = maybeDesugar(AST, T);
    std::string TypeName = Desugared.getAsString(TypeHintPolicy);
    if (T != Desugared && !shouldPrintTypeHint(TypeName)) {
      // If the desugared type is too long to display, fallback to the sugared
      // type.
      TypeName = T.getAsString(TypeHintPolicy);
    }
    if (shouldPrintTypeHint(TypeName))
      addInlayHint(R, HintSide::Right, InlayHintKind::Type, Prefix, TypeName,
                   /*Suffix=*/"");
  }

  void addDesignatorHint(SourceRange R, llvm::StringRef Text) {
    addInlayHint(R, HintSide::Left, InlayHintKind::Designator,
                 /*Prefix=*/"", Text, /*Suffix=*/"=");
  }

  bool shouldPrintTypeHint(llvm::StringRef TypeName) const noexcept {
    return Cfg.InlayHints.TypeNameLimit == 0 ||
           TypeName.size() < Cfg.InlayHints.TypeNameLimit;
  }

  void addBlockEndHint(SourceRange BraceRange, StringRef DeclPrefix,
                       StringRef Name, StringRef OptionalPunctuation) {
    auto HintRange = computeBlockEndHintRange(BraceRange, OptionalPunctuation);
    if (!HintRange)
      return;

    std::string Label = DeclPrefix.str();
    if (!Label.empty() && !Name.empty())
      Label += ' ';
    Label += Name;

    constexpr unsigned HintMaxLengthLimit = 60;
    if (Label.length() > HintMaxLengthLimit)
      return;

    addInlayHint(*HintRange, HintSide::Right, InlayHintKind::BlockEnd, " // ",
                 Label, "");
  }

  // Compute the LSP range to attach the block end hint to, if any allowed.
  // 1. "}" is the last non-whitespace character on the line. The range of "}"
  // is returned.
  // 2. After "}", if the trimmed trailing text is exactly
  // `OptionalPunctuation`, say ";". The range of "} ... ;" is returned.
  // Otherwise, the hint shouldn't be shown.
  std::optional<Range> computeBlockEndHintRange(SourceRange BraceRange,
                                                StringRef OptionalPunctuation) {
    constexpr unsigned HintMinLineLimit = 2;

    auto &SM = AST.getSourceManager();
    auto [BlockBeginFileId, BlockBeginOffset] =
        SM.getDecomposedLoc(SM.getFileLoc(BraceRange.getBegin()));
    auto RBraceLoc = SM.getFileLoc(BraceRange.getEnd());
    auto [RBraceFileId, RBraceOffset] = SM.getDecomposedLoc(RBraceLoc);

    // Because we need to check the block satisfies the minimum line limit, we
    // require both source location to be in the main file. This prevents hint
    // to be shown in weird cases like '{' is actually in a "#include", but it's
    // rare anyway.
    if (BlockBeginFileId != MainFileID || RBraceFileId != MainFileID)
      return std::nullopt;

    StringRef RestOfLine = MainFileBuf.substr(RBraceOffset).split('\n').first;
    if (!RestOfLine.starts_with("}"))
      return std::nullopt;

    StringRef TrimmedTrailingText = RestOfLine.drop_front().trim();
    if (!TrimmedTrailingText.empty() &&
        TrimmedTrailingText != OptionalPunctuation)
      return std::nullopt;

    auto BlockBeginLine = SM.getLineNumber(BlockBeginFileId, BlockBeginOffset);
    auto RBraceLine = SM.getLineNumber(RBraceFileId, RBraceOffset);

    // Don't show hint on trivial blocks like `class X {};`
    if (BlockBeginLine + HintMinLineLimit - 1 > RBraceLine)
      return std::nullopt;

    // This is what we attach the hint to, usually "}" or "};".
    StringRef HintRangeText = RestOfLine.take_front(
        TrimmedTrailingText.empty()
            ? 1
            : TrimmedTrailingText.bytes_end() - RestOfLine.bytes_begin());

    Position HintStart = sourceLocToPosition(SM, RBraceLoc);
    Position HintEnd = sourceLocToPosition(
        SM, RBraceLoc.getLocWithOffset(HintRangeText.size()));
    return Range{HintStart, HintEnd};
  }

  std::vector<InlayHint> &Results;
  ASTContext &AST;
  const syntax::TokenBuffer &Tokens;
  const Config &Cfg;
  std::optional<Range> RestrictRange;
  FileID MainFileID;
  StringRef MainFileBuf;
  const HeuristicResolver *Resolver;
  PrintingPolicy TypeHintPolicy;
};

} // namespace

std::vector<InlayHint> inlayHints(ParsedAST &AST,
                                  std::optional<Range> RestrictRange) {
  std::vector<InlayHint> Results;
  const auto &Cfg = Config::current();
  if (!Cfg.InlayHints.Enabled)
    return Results;
  InlayHintVisitor Visitor(Results, AST, Cfg, std::move(RestrictRange));
  Visitor.TraverseAST(AST.getASTContext());

  // De-duplicate hints. Duplicates can sometimes occur due to e.g. explicit
  // template instantiations.
  llvm::sort(Results);
  Results.erase(std::unique(Results.begin(), Results.end()), Results.end());

  return Results;
}

} // namespace clangd
} // namespace clang