[clang] Template Specialization Resugaring - TypeDecl

This is the introductory patch for a larger work which intends to solve the long standing C++ issue with losing type sugar when acessing template specializations. The well known example here is specializing a template with `std::string`, but getting diagnostics related to `std::basic_string<char>` instead. This implements a transform which, upon member access, propagates type sugar from the naming context into the accessed entity. It also implements a single use of this transform, resugaring access to TypeDecls. For more details and discussion see: https://discourse.llvm.org/t/rfc-improving-diagnostics-with-template-specialization-resugaring/64294 This is ready for review, although maybe not finished and there is some more stuff that could be done either here or in follow ups. * Its worth exploring if a global resugaring cache is worthwhile, besides the current operational cache. A global cache would be more expensive to index, so there is a tradeoff, and maybe should be used of the whole result of the operation, while keeping the existing cache for sub-results. * It would be ideal if the transform could live in ASTContext instead of Sema. There are a few dependencies that would have to be tackled. * Template arguments deduced for partial specializations. * Some kinds of type adjustments currently require Sema. Differential Revision: https://reviews.llvm.org/D127695

Author: mizvekov

clang-tools-extra/clang-tidy/readability/QualifiedAutoCheck.cpp

@@ -126,7 +126,7 @@ void QualifiedAutoCheck::registerMatchers(MatchFinder *Finder) {
  auto UnlessFunctionType = unless(hasUnqualifiedDesugaredType(functionType()));
  auto IsAutoDeducedToPointer = [](const auto &...InnerMatchers) {
  return autoType(hasDeducedType(
- hasUnqualifiedDesugaredType(pointerType(pointee(InnerMatchers...)))));
+ hasCanonicalType(pointerType(pointee(InnerMatchers...)))));
  };
 
  Finder->addMatcher(

clang/include/clang/AST/ASTContext.h

@@ -1319,8 +1319,6 @@ class ASTContext : public RefCountedBase<ASTContext> {
 
  QualType getTypeDeclTypeSlow(const TypeDecl *Decl) const;
 
- QualType getPipeType(QualType T, bool ReadOnly) const;
-
 public:
  /// Return the uniqued reference to the type for an address space
  /// qualified type with the specified type and address space.
@@ -1500,6 +1498,9 @@ class ASTContext : public RefCountedBase<ASTContext> {
  /// blocks.
  QualType getBlockDescriptorType() const;
 
+ // Return a pipe type for the specified type.
+ QualType getPipeType(QualType T, bool ReadOnly) const;
+
  /// Return a read_only pipe type for the specified type.
  QualType getReadPipeType(QualType T) const;
 
@@ -1901,10 +1902,10 @@ class ASTContext : public RefCountedBase<ASTContext> {
  /// C++11 decltype.
  QualType getDecltypeType(Expr *e, QualType UnderlyingType) const;
 
- QualType getPackIndexingType(QualType Pattern, Expr *IndexExpr,
-   bool FullySubstituted = false,
-  ArrayRef<QualType> Expansions = {},
-  int Index = -1) const;
+ QualType getPackIndexingType(
+ QualType Pattern, Expr *IndexExpr, bool FullySubstituted = false,
+ ArrayRef<QualType> Expansions = {},
+ std::optional<unsigned> SelectedIndex = std::nullopt) const;
 
  /// Unary type transforms
  QualType getUnaryTransformType(QualType BaseType, QualType UnderlyingType,

clang/include/clang/AST/Type.h

@@ -643,10 +643,10 @@ class Qualifiers {
  void addQualifiers(Qualifiers Q) {
  // If the other set doesn't have any non-boolean qualifiers, just
  // bit-or it in.
- if (!(Q.Mask & ~CVRMask))
+ if (!(Q.Mask & ~CVRUMask))
  Mask |= Q.Mask;
  else {
- Mask |= (Q.Mask & CVRMask);
+ Mask |= (Q.Mask & CVRUMask);
  if (Q.hasAddressSpace())
  addAddressSpace(Q.getAddressSpace());
  if (Q.hasObjCGCAttr())
@@ -662,10 +662,10 @@ class Qualifiers {
  void removeQualifiers(Qualifiers Q) {
  // If the other set doesn't have any non-boolean qualifiers, just
  // bit-and the inverse in.
- if (!(Q.Mask & ~CVRMask))
+ if (!(Q.Mask & ~CVRUMask))
  Mask &= ~Q.Mask;
  else {
- Mask &= ~(Q.Mask & CVRMask);
+ Mask &= ~(Q.Mask & CVRUMask);
  if (getObjCGCAttr() == Q.getObjCGCAttr())
  removeObjCGCAttr();
  if (getObjCLifetime() == Q.getObjCLifetime())
@@ -805,12 +805,13 @@ class Qualifiers {
 
  static constexpr uint64_t UMask = 0x8;
  static constexpr uint64_t UShift = 3;
+ static constexpr uint64_t CVRUMask = CVRMask | UMask;
  static constexpr uint64_t GCAttrMask = 0x30;
  static constexpr uint64_t GCAttrShift = 4;
  static constexpr uint64_t LifetimeMask = 0x1C0;
  static constexpr uint64_t LifetimeShift = 6;
  static constexpr uint64_t AddressSpaceMask =
- ~(CVRMask | UMask | GCAttrMask | LifetimeMask);
+ ~(CVRUMask | GCAttrMask | LifetimeMask);
  static constexpr uint64_t AddressSpaceShift = 9;
  static constexpr uint64_t PtrAuthShift = 32;
  static constexpr uint64_t PtrAuthMask = uint64_t(0xffffffff) << PtrAuthShift;

clang/include/clang/Sema/Sema.h

@@ -3193,7 +3193,8 @@ class Sema final : public SemaBase {
  /// Returns the TypeDeclType for the given type declaration,
  /// as ASTContext::getTypeDeclType would, but
  /// performs the required semantic checks for name lookup of said entity.
- QualType getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
+ QualType getTypeDeclType(const NestedNameSpecifier *NNS,
+ DeclContext *LookupCtx, DiagCtorKind DCK,
  TypeDecl *TD, SourceLocation NameLoc);
 
  /// If the identifier refers to a type name within this scope,
@@ -13980,6 +13981,8 @@ class Sema final : public SemaBase {
  FunctionDecl *SubstSpaceshipAsEqualEqual(CXXRecordDecl *RD,
  FunctionDecl *Spaceship);
 
+ QualType resugar(const NestedNameSpecifier *NNS, QualType T);
+
  /// Performs template instantiation for all implicit template
  /// instantiations we have seen until this point.
  void PerformPendingInstantiations(bool LocalOnly = false,
@@ -14972,7 +14975,8 @@ class Sema final : public SemaBase {
  /// wasn't specified explicitly. This handles method types formed from
  /// function type typedefs and typename template arguments.
  void adjustMemberFunctionCC(QualType &T, bool HasThisPointer,
- bool IsCtorOrDtor, SourceLocation Loc);
+ bool IsCtorOrDtor, bool IsDeduced,
+ SourceLocation Loc);
 
  // Check if there is an explicit attribute, but only look through parens.
  // The intent is to look for an attribute on the current declarator, but not

clang/lib/AST/ASTContext.cpp

@@ -6385,13 +6385,14 @@ QualType ASTContext::getDecltypeType(Expr *e, QualType UnderlyingType) const {
  return QualType(dt, 0);
 }
 
-QualType ASTContext::getPackIndexingType(QualType Pattern, Expr *IndexExpr,
- bool FullySubstituted,
- ArrayRef<QualType> Expansions,
- int Index) const {
+QualType
+ASTContext::getPackIndexingType(QualType Pattern, Expr *IndexExpr,
+ bool FullySubstituted,
+ ArrayRef<QualType> Expansions,
+ std::optional<unsigned> SelectedIndex) const {
  QualType Canonical;
- if (FullySubstituted && Index != -1) {
- Canonical = getCanonicalType(Expansions[Index]);
+ if (FullySubstituted && SelectedIndex) {
+ Canonical = getCanonicalType(Expansions[*SelectedIndex]);
  } else {
  llvm::FoldingSetNodeID ID;
  PackIndexingType::Profile(ID, *this, Pattern.getCanonicalType(), IndexExpr,
@@ -14103,9 +14104,7 @@ static QualType getCommonNonSugarTypeNode(ASTContext &Ctx, const Type *X,
  case Type::Pipe: {
  const auto *PX = cast<PipeType>(X), *PY = cast<PipeType>(Y);
  assert(PX->isReadOnly() == PY->isReadOnly());
- auto MP = PX->isReadOnly() ? &ASTContext::getReadPipeType
- : &ASTContext::getWritePipeType;
- return (Ctx.*MP)(getCommonElementType(Ctx, PX, PY));
+ return Ctx.getPipeType(getCommonElementType(Ctx, PX, PY), PX->isReadOnly());
  }
  case Type::TemplateTypeParm: {
  const auto *TX = cast<TemplateTypeParmType>(X),

clang/lib/Sema/SemaCXXScopeSpec.cpp

@@ -644,8 +644,9 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
  return false;
  }
 
- QualType T =
- Context.getTypeDeclType(cast<TypeDecl>(SD->getUnderlyingDecl()));
+ QualType T = resugar(
+ SS.getScopeRep(),
+ Context.getTypeDeclType(cast<TypeDecl>(SD->getUnderlyingDecl())));
 
  if (T->isEnumeralType())
  Diag(IdInfo.IdentifierLoc, diag::warn_cxx98_compat_enum_nested_name_spec);

clang/lib/Sema/SemaCoroutine.cpp

@@ -113,6 +113,7 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
  }
  // The promise type is required to be a class type.
  QualType PromiseType = S.Context.getTypeDeclType(Promise);
+ // FIXME: resugar PromiseType.
 
  auto buildElaboratedType = [&]() {
  auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, S.getStdNamespace());

clang/lib/Sema/SemaDecl.cpp

@@ -139,7 +139,8 @@ class TypeNameValidatorCCC final : public CorrectionCandidateCallback {
 
 } // end anonymous namespace
 
-QualType Sema::getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
+QualType Sema::getTypeDeclType(const NestedNameSpecifier *NNS,
+ DeclContext *LookupCtx, DiagCtorKind DCK,
  TypeDecl *TD, SourceLocation NameLoc) {
  auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
  auto *FoundRD = dyn_cast<CXXRecordDecl>(TD);
@@ -156,7 +157,7 @@ QualType Sema::getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
 
  DiagnoseUseOfDecl(TD, NameLoc);
  MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
- return Context.getTypeDeclType(TD);
+ return resugar(NNS, Context.getTypeDeclType(TD));
 }
 
 namespace {
@@ -534,7 +535,7 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
  // C++ [class.qual]p2: A lookup that would find the injected-class-name
  // instead names the constructors of the class, except when naming a class.
  // This is ill-formed when we're not actually forming a ctor or dtor name.
- T = getTypeDeclType(LookupCtx,
+ T = getTypeDeclType(SS ? SS->getScopeRep() : nullptr, LookupCtx,
  IsImplicitTypename ? DiagCtorKind::Implicit
  : DiagCtorKind::None,
  TD, NameLoc);
@@ -9872,7 +9873,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
  if (D.isFirstDeclarationOfMember())
  adjustMemberFunctionCC(
  R, !(D.isStaticMember() || D.isExplicitObjectMemberFunction()),
- D.isCtorOrDtor(), D.getIdentifierLoc());
+ D.isCtorOrDtor(), /*IsDeduced=*/false, D.getIdentifierLoc());
 
  bool isFriend = false;
  FunctionTemplateDecl *FunctionTemplate = nullptr;

clang/lib/Sema/SemaDeclCXX.cpp

@@ -1248,7 +1248,7 @@ static QualType getTupleLikeElementType(Sema &S, SourceLocation Loc,
  S.Diag(R.getRepresentativeDecl()->getLocation(), diag::note_declared_at);
  return QualType();
  }
-
+ // FIXME: resugar
  return S.Context.getTypeDeclType(TD);
 }