[clang] Template Specialization Resugaring - Template Type Alias

This implements an additional user of the resugaring transform: the pattern of template type aliases. For more details and discussion see: https://discourse.llvm.org/t/rfc-improving-diagnostics-with-template-specialization-resugaring/64294 Differential Revision: https://reviews.llvm.org/D137199

Author: mizvekov

clang/include/clang/Sema/Sema.h

@@ -11509,7 +11509,8 @@ class Sema final : public SemaBase {
 
  void NoteAllFoundTemplates(TemplateName Name);
 
- QualType CheckTemplateIdType(TemplateName Template,
+ QualType CheckTemplateIdType(const NestedNameSpecifier *NNS,
+ TemplateName Template,
  SourceLocation TemplateLoc,
  TemplateArgumentListInfo &TemplateArgs);
 

clang/lib/Sema/SemaCXXScopeSpec.cpp

@@ -907,7 +907,8 @@ bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
 
  // We were able to resolve the template name to an actual template.
  // Build an appropriate nested-name-specifier.
- QualType T = CheckTemplateIdType(Template, TemplateNameLoc, TemplateArgs);
+ QualType T = CheckTemplateIdType(SS.getScopeRep(), Template, TemplateNameLoc,
+ TemplateArgs);
  if (T.isNull())
  return true;
 

clang/lib/Sema/SemaCoroutine.cpp

@@ -90,7 +90,7 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
 
  // Build the template-id.
  QualType CoroTrait =
- S.CheckTemplateIdType(TemplateName(CoroTraits), KwLoc, Args);
+ S.CheckTemplateIdType(nullptr, TemplateName(CoroTraits), KwLoc, Args);
  if (CoroTrait.isNull())
  return QualType();
  if (S.RequireCompleteType(KwLoc, CoroTrait,
@@ -169,7 +169,7 @@ static QualType lookupCoroutineHandleType(Sema &S, QualType PromiseType,
 
  // Build the template-id.
  QualType CoroHandleType =
- S.CheckTemplateIdType(TemplateName(CoroHandle), Loc, Args);
+ S.CheckTemplateIdType(nullptr, TemplateName(CoroHandle), Loc, Args);
  if (CoroHandleType.isNull())
  return QualType();
  if (S.RequireCompleteType(Loc, CoroHandleType,

clang/lib/Sema/SemaDeclCXX.cpp

@@ -1140,7 +1140,8 @@ static bool lookupStdTypeTraitMember(Sema &S, LookupResult &TraitMemberLookup,
  }
 
  // Build the template-id.
- QualType TraitTy = S.CheckTemplateIdType(TemplateName(TraitTD), Loc, Args);
+ QualType TraitTy =
+ S.CheckTemplateIdType(nullptr, TemplateName(TraitTD), Loc, Args);
  if (TraitTy.isNull())
  return true;
  if (!S.isCompleteType(Loc, TraitTy)) {
@@ -12163,7 +12164,8 @@ QualType Sema::BuildStdInitializerList(QualType Element, SourceLocation Loc) {
  Context.getTrivialTypeSourceInfo(Element,
  Loc)));
 
- QualType T = CheckTemplateIdType(TemplateName(StdInitializerList), Loc, Args);
+ QualType T =
+ CheckTemplateIdType(nullptr, TemplateName(StdInitializerList), Loc, Args);
  if (T.isNull())
  return QualType();
 

clang/lib/Sema/SemaTemplate.cpp

@@ -3827,15 +3827,16 @@ void Sema::NoteAllFoundTemplates(TemplateName Name) {
  }
 }
 
-static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
+static QualType builtinCommonTypeImpl(Sema &S, const NestedNameSpecifier *NNS,
+ TemplateName BaseTemplate,
  SourceLocation TemplateLoc,
  ArrayRef<TemplateArgument> Ts) {
  auto lookUpCommonType = [&](TemplateArgument T1,
  TemplateArgument T2) -> QualType {
  // Don't bother looking for other specializations if both types are
  // builtins - users aren't allowed to specialize for them
  if (T1.getAsType()->isBuiltinType() && T2.getAsType()->isBuiltinType())
- return builtinCommonTypeImpl(S, BaseTemplate, TemplateLoc, {T1, T2});
+ return builtinCommonTypeImpl(S, NNS, BaseTemplate, TemplateLoc, {T1, T2});
 
  TemplateArgumentListInfo Args;
  Args.addArgument(TemplateArgumentLoc(
@@ -3849,7 +3850,7 @@ static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
  Sema::ContextRAII TUContext(S, S.Context.getTranslationUnitDecl());
 
  QualType BaseTemplateInst =
- S.CheckTemplateIdType(BaseTemplate, TemplateLoc, Args);
+ S.CheckTemplateIdType(NNS, BaseTemplate, TemplateLoc, Args);
 
  if (SFINAE.hasErrorOccurred())
  return QualType();
@@ -3962,8 +3963,8 @@ static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
 }
 
 static QualType checkBuiltinTemplateIdType(
- Sema &SemaRef, TemplateName Name, BuiltinTemplateDecl *BTD,
- ArrayRef<TemplateArgument> SugaredConverted,
+ Sema &SemaRef, const NestedNameSpecifier *NNS, TemplateName Name,
+ BuiltinTemplateDecl *BTD, ArrayRef<TemplateArgument> SugaredConverted,
  ArrayRef<TemplateArgument> CanonicalConverted, SourceLocation TemplateLoc,
  TemplateArgumentListInfo &TemplateArgs) {
  ASTContext &Context = SemaRef.getASTContext();
@@ -4015,7 +4016,7 @@ static QualType checkBuiltinTemplateIdType(
  // The first template argument will be reused as the template decl that
  // our synthetic template arguments will be applied to.
  QualType Result =
- SemaRef.CheckTemplateIdType(SugaredConverted[0].getAsTemplate(),
+ SemaRef.CheckTemplateIdType(NNS, SugaredConverted[0].getAsTemplate(),
  TemplateLoc, SyntheticTemplateArgs);
  return SemaRef.Context.getTemplateSpecializationType(
  Name, TemplateArgs.arguments(), SugaredConverted, CanonicalConverted,
@@ -4065,14 +4066,16 @@ static QualType checkBuiltinTemplateIdType(
  QualType HasNoTypeMember = SugaredConverted[2].getAsType();
  ArrayRef<TemplateArgument> Ts = SugaredConverted[3].getPackAsArray();
  QualType Result = HasNoTypeMember;
- if (auto CT = builtinCommonTypeImpl(SemaRef, BaseTemplate, TemplateLoc, Ts);
+ if (auto CT =
+ builtinCommonTypeImpl(SemaRef, NNS, BaseTemplate, TemplateLoc, Ts);
  !CT.isNull()) {
  TemplateArgumentListInfo TAs;
  TAs.addArgument(TemplateArgumentLoc(
  TemplateArgument(CT), SemaRef.Context.getTrivialTypeSourceInfo(
  CT, TemplateArgs[1].getLocation())));
 
- Result = SemaRef.CheckTemplateIdType(HasTypeMember, TemplateLoc, TAs);
+ Result =
+ SemaRef.CheckTemplateIdType(NNS, HasTypeMember, TemplateLoc, TAs);
  }
  return SemaRef.Context.getTemplateSpecializationType(
  Name, TemplateArgs.arguments(), SugaredConverted, CanonicalConverted,
@@ -4220,7 +4223,8 @@ Sema::findFailedBooleanCondition(Expr *Cond) {
  return { FailedCond, Description };
 }
 
-QualType Sema::CheckTemplateIdType(TemplateName Name,
+QualType Sema::CheckTemplateIdType(const NestedNameSpecifier *NNS,
+ TemplateName Name,
  SourceLocation TemplateLoc,
  TemplateArgumentListInfo &TemplateArgs) {
  // FIXME: 'getUnderlying' loses SubstTemplateTemplateParm nodes from alias
@@ -4299,9 +4303,9 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
  if (!AliasTemplate->getDeclContext()->isFileContext())
  SavedContext.emplace(*this, AliasTemplate->getDeclContext());
 
- CanonType =
-  SubstType(Pattern->getUnderlyingType(), TemplateArgLists,
- AliasTemplate->getLocation(), AliasTemplate->getDeclName());
+ QualType T = resugar(NNS, Pattern->getUnderlyingType());
+ CanonType = SubstType(T, TemplateArgLists, AliasTemplate->getLocation(),
+   AliasTemplate->getDeclName());
  if (CanonType.isNull()) {
  // If this was enable_if and we failed to find the nested type
  // within enable_if in a SFINAE context, dig out the specific
@@ -4338,9 +4342,9 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
  return QualType();
  }
  } else if (auto *BTD = dyn_cast<BuiltinTemplateDecl>(Template)) {
- return checkBuiltinTemplateIdType(*this, Name, BTD, CTAI.SugaredConverted,
-  CTAI.CanonicalConverted, TemplateLoc,
-   TemplateArgs);
+ return checkBuiltinTemplateIdType(
+ *this, NNS, Name, BTD, CTAI.SugaredConverted, CTAI.CanonicalConverted,
+ TemplateLoc, TemplateArgs);
  } else if (Name.isDependent() ||
  TemplateSpecializationType::anyDependentTemplateArguments(
  TemplateArgs, CTAI.CanonicalConverted)) {
@@ -4583,7 +4587,8 @@ TypeResult Sema::ActOnTemplateIdType(
  return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
  }
 
- QualType SpecTy = CheckTemplateIdType(Template, TemplateIILoc, TemplateArgs);
+ QualType SpecTy = CheckTemplateIdType(SS.getScopeRep(), Template,
+ TemplateIILoc, TemplateArgs);
  if (SpecTy.isNull())
  return true;
 
@@ -4664,7 +4669,8 @@ TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
  Diag(TAT->getLocation(), diag::note_declared_at);
  }
 
- QualType Result = CheckTemplateIdType(Template, TemplateLoc, TemplateArgs);
+ QualType Result = CheckTemplateIdType(SS.getScopeRep(), Template, TemplateLoc,
+ TemplateArgs);
  if (Result.isNull())
  return TypeResult(true);
 
@@ -11446,7 +11452,8 @@ Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
  return CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
  }
 
- QualType T = CheckTemplateIdType(Template, TemplateIILoc, TemplateArgs);
+ QualType T = CheckTemplateIdType(SS.getScopeRep(), Template, TemplateIILoc,
+ TemplateArgs);
  if (T.isNull())
  return true;
 

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -6816,7 +6816,8 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
  Args.addArgument(
  getTrivialTemplateArgumentLoc(UnpackedArg, QualType(), Loc));
  }
- QualType T = CheckTemplateIdType(TemplateName(TD), Loc, Args);
+ QualType T =
+ CheckTemplateIdType(/*NNS=*/nullptr, TemplateName(TD), Loc, Args);
  // We may get a non-null type with errors, in which case
  // `getAsCXXRecordDecl` will return `nullptr`. For instance, this
  // happens when one of the template arguments is an invalid

clang/lib/Sema/TreeTransform.h

@@ -17347,7 +17347,8 @@ QualType TreeTransform<Derived>::RebuildTemplateSpecializationType(
  TemplateName Template,
  SourceLocation TemplateNameLoc,
  TemplateArgumentListInfo &TemplateArgs) {
- return SemaRef.CheckTemplateIdType(Template, TemplateNameLoc, TemplateArgs);
+ return SemaRef.CheckTemplateIdType(nullptr, Template, TemplateNameLoc,
+ TemplateArgs);
 }
 
 template<typename Derived>

clang/test/AST/ast-dump-template-decls.cpp

@@ -126,7 +126,7 @@ using type2 = typename C<int>::type1<void>;
 // CHECK-NEXT: SubstTemplateTypeParmType 0x{{[^ ]*}} 'void' sugar class depth 0 index 0 U final
 // CHECK-NEXT: TypeAliasTemplate 0x{{[^ ]*}} 'type1'
 // CHECK-NEXT: BuiltinType 0x{{[^ ]*}} 'void'
-// CHECK-NEXT: SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar class depth 0 index 0 T
+// CHECK-NEXT: SubstTemplateTypeParmType 0x{{[^ ]*}} 'int' sugar class depth 0 index 0 T final
 // CHECK-NEXT: ClassTemplateSpecialization 0x{{[^ ]*}} 'C'
 // CHECK-NEXT: BuiltinType 0x{{[^ ]*}} 'int'
 } // namespace PR55886
@@ -138,7 +138,7 @@ template <typename... T> struct D {
  };
 };
 template struct D<float, char>::bind<int, short>;
-// CHECK: TypeAliasDecl 0x{{[^ ]*}} <line:{{[1-9]+}}:5, col:45> col:11 bound_type 'int (int (*)(float, int), int (*)(char, short))'
+// CHECK: TypeAliasDecl 0x{{[^ ]*}} <line:{{[0-9]+}}:5, col:45> col:11 bound_type 'int (int (*)(float, int), int (*)(char, short))'
 // CHECK: FunctionProtoType 0x{{[^ ]*}} 'int (int (*)(float, int), int (*)(char, short))' cdecl
 // CHECK: FunctionProtoType 0x{{[^ ]*}} 'int (float, int)' cdecl
 // CHECK: SubstTemplateTypeParmType 0x{{[^ ]*}} 'float' sugar typename depth 0 index 0 ... T pack_index 1{{$}}

clang/test/Sema/Resugar/resugar-types.cpp

@@ -88,7 +88,7 @@ template <class E> struct foo {
 };
 using T1 = foo<Bar>::apply<char>;
 TEST_NOT(T1::type1);
-TEST_NOT(T1::type2); // FIXME: Needs resugaring on the pattern of template type aliases.
+TEST(T1::type2);
 
 using T2 = foo<int>::apply<Bar>;
 TEST(T2::type1);
@@ -106,7 +106,7 @@ template <typename... Cs> struct foo {
 };
 using T1 = foo<Bar>::bind<char>;
 TEST_NOT(T1::type1);
-TEST_NOT(T1::type2); // FIXME: Needs resugaring on the pattern of template type aliases.
+TEST(T1::type2);
 
 using T2 = foo<int>::bind<Bar>;
 TEST(T2::type1);
@@ -148,7 +148,7 @@ template <typename... Ts> using Z = Y<Ts...>;
 
 using T1 = typename foo<Z, Bar>::template bind<int>;
 TEST_NOT(typename T1::type1);
-TEST_NOT(typename T1::type2); // FIXME: Needs resugaring on the pattern of template type aliases.
+TEST(typename T1::type2);
 
 using T2 = typename foo<Z, int>::template bind<Bar>;
 TEST(typename T2::type1);