The lambda call inside of a type alias

clang/docs/ReleaseNotes.rst

@@ -344,6 +344,8 @@ Bug Fixes to C++ Support
   when one of the function had more specialized templates.
   Fixes (`#82509 <https://github.com/llvm/llvm-project/issues/82509>`_)
   and (`#74494 <https://github.com/llvm/llvm-project/issues/74494>`_)
+- Clang now supports direct lambda calls inside of a type alias template declarations.
+  This addresses (#GH70601), (#GH76674), (#GH79555), (#GH81145) and so on.
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/DeclCXX.h

@@ -1869,6 +1869,10 @@ class CXXRecordDecl : public RecordDecl {
     DL.MethodTyInfo = TS;
   }
 
+  void setLambdaDependencyKind(unsigned Kind) {
+    getLambdaData().DependencyKind = Kind;
+  }
+
   void setLambdaIsGeneric(bool IsGeneric) {
     assert(DefinitionData && DefinitionData->IsLambda &&
            "setting lambda property of non-lambda class");

clang/include/clang/Sema/Sema.h

@@ -10145,6 +10145,8 @@ class Sema final {
 
       /// We are building deduction guides for a class.
       BuildingDeductionGuides,
+
+      TypeAliasTemplateInstantiation,
     } Kind;
 
     /// Was the enclosing context a non-instantiation SFINAE context?
@@ -10234,6 +10236,12 @@ class Sema final {
                           FunctionDecl *Entity, ExceptionSpecification,
                           SourceRange InstantiationRange = SourceRange());
 
+    /// Note that we are instantiating a type alias template declaration.
+    InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
+                          TypeAliasTemplateDecl *Template,
+                          ArrayRef<TemplateArgument> TemplateArgs,
+                          SourceRange InstantiationRange = SourceRange());
+
     /// Note that we are instantiating a default argument in a
     /// template-id.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,

clang/lib/Frontend/FrontendActions.cpp

@@ -452,6 +452,8 @@ class DefaultTemplateInstCallback : public TemplateInstantiationCallback {
       return "BuildingBuiltinDumpStructCall";
     case CodeSynthesisContext::BuildingDeductionGuides:
       return "BuildingDeductionGuides";
+    case Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation:
+      return "TypeAliasTemplateInstantiation";
     }
     return "";
   }

clang/lib/Sema/SemaConcept.cpp

@@ -615,14 +615,13 @@ bool Sema::SetupConstraintScope(
     // reference the original primary template.
     // We walk up the instantiated template chain so that nested lambdas get
     // handled properly.
-    for (FunctionTemplateDecl *FromMemTempl =
-             PrimaryTemplate->getInstantiatedFromMemberTemplate();
-         FromMemTempl;
-         FromMemTempl = FromMemTempl->getInstantiatedFromMemberTemplate()) {
-      if (addInstantiatedParametersToScope(FD, FromMemTempl->getTemplatedDecl(),
-                                           Scope, MLTAL))
-        return true;
-    }
+    FunctionTemplateDecl *FromMemTempl =
+        PrimaryTemplate->getInstantiatedFromMemberTemplate();
+    while (FromMemTempl && FromMemTempl->getInstantiatedFromMemberTemplate())
+      FromMemTempl = FromMemTempl->getInstantiatedFromMemberTemplate();
+    if (FromMemTempl && addInstantiatedParametersToScope(
+                            FD, FromMemTempl->getTemplatedDecl(), Scope, MLTAL))
+      return true;
 
     return false;
   }

clang/lib/Sema/SemaTemplate.cpp

@@ -4343,9 +4343,12 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
     if (Inst.isInvalid())
       return QualType();
 
-    CanonType = SubstType(Pattern->getUnderlyingType(),
-                          TemplateArgLists, AliasTemplate->getLocation(),
-                          AliasTemplate->getDeclName());
+    InstantiatingTemplate InstTemplate(
+        *this, Pattern->getTypeSourceInfo()->getTypeLoc().getBeginLoc(),
+        AliasTemplate, TemplateArgLists.getInnermost());
+    CanonType =
+        SubstType(Pattern->getUnderlyingType(), 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

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -283,7 +283,8 @@ Response HandleFunctionTemplateDecl(const FunctionTemplateDecl *FTD,
   return Response::ChangeDecl(FTD->getLexicalDeclContext());
 }
 
-Response HandleRecordDecl(const CXXRecordDecl *Rec,
+Response HandleRecordDecl(Sema &SemaRef,
+                          const CXXRecordDecl *Rec,
                           MultiLevelTemplateArgumentList &Result,
                           ASTContext &Context,
                           bool ForConstraintInstantiation) {
@@ -314,9 +315,42 @@ Response HandleRecordDecl(const CXXRecordDecl *Rec,
 
   // This is to make sure we pick up the VarTemplateSpecializationDecl that this
   // lambda is defined inside of.
-  if (Rec->isLambda())
+  if (Rec->isLambda()) {
     if (const Decl *LCD = Rec->getLambdaContextDecl())
       return Response::ChangeDecl(LCD);
+    if (ForConstraintInstantiation && !SemaRef.CodeSynthesisContexts.empty()) {
+      for (auto &CSC : llvm::reverse(SemaRef.CodeSynthesisContexts)) {
+        if (CSC.Kind == Sema::CodeSynthesisContext::SynthesisKind::TypeAliasTemplateInstantiation) {
+          auto *TATD = cast<TypeAliasTemplateDecl>(CSC.Entity), *CurrentTATD = TATD;
+          FunctionDecl *LambdaCallOperator = Rec->getLambdaCallOperator();
+          while (true) {
+            auto *FTD = dyn_cast_if_present<FunctionTemplateDecl>(
+                LambdaCallOperator->getDescribedTemplate());
+            if (FTD && FTD->getInstantiatedFromMemberTemplate()) {
+              LambdaCallOperator =
+                  FTD->getInstantiatedFromMemberTemplate()->getTemplatedDecl();
+            } else if (auto *Prev = cast<CXXMethodDecl>(LambdaCallOperator)
+                                        ->getInstantiatedFromMemberFunction())
+              LambdaCallOperator = Prev;
+            else
+              break;
+          }
+          while (TATD->getInstantiatedFromMemberTemplate())
+            TATD = TATD->getInstantiatedFromMemberTemplate();
+          // Constraint template parameters have a deeper depth.
+          if (cast<CXXRecordDecl>(LambdaCallOperator->getDeclContext())
+                      ->getTemplateDepth() == TATD->getTemplateDepth() &&
+              getLambdaAwareParentOfDeclContext(LambdaCallOperator) ==
+                  TATD->getDeclContext()) {
+            Result.addOuterTemplateArguments(CurrentTATD,
+                                             CSC.template_arguments(),
+                                             /*Final=*/false);
+            return Response::ChangeDecl(CurrentTATD->getDeclContext());
+          }
+        }
+      }
+    }
+  }
 
   return Response::UseNextDecl(Rec);
 }
@@ -413,7 +447,7 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
       R = HandleFunction(Function, Result, Pattern, RelativeToPrimary,
                          ForConstraintInstantiation);
     } else if (const auto *Rec = dyn_cast<CXXRecordDecl>(CurDecl)) {
-      R = HandleRecordDecl(Rec, Result, Context, ForConstraintInstantiation);
+      R = HandleRecordDecl(*this, Rec, Result, Context, ForConstraintInstantiation);
     } else if (const auto *CSD =
                    dyn_cast<ImplicitConceptSpecializationDecl>(CurDecl)) {
       R = HandleImplicitConceptSpecializationDecl(CSD, Result);
@@ -470,6 +504,7 @@ bool Sema::CodeSynthesisContext::isInstantiationRecord() const {
   case BuildingBuiltinDumpStructCall:
   case LambdaExpressionSubstitution:
   case BuildingDeductionGuides:
+  case TypeAliasTemplateInstantiation:
     return false;
 
   // This function should never be called when Kind's value is Memoization.
@@ -615,6 +650,15 @@ Sema::InstantiatingTemplate::InstantiatingTemplate(
           PointOfInstantiation, InstantiationRange, Param, Template,
           TemplateArgs) {}
 
+Sema::InstantiatingTemplate::InstantiatingTemplate(
+    Sema &SemaRef, SourceLocation PointOfInstantiation,
+    TypeAliasTemplateDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
+    SourceRange InstantiationRange)
+    : InstantiatingTemplate(
+          SemaRef, Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation,
+          PointOfInstantiation, InstantiationRange, /*Entity=*/Template,
+          nullptr, TemplateArgs) {}
+
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Template,
     NamedDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
@@ -1132,6 +1176,8 @@ void Sema::PrintInstantiationStack() {
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_building_deduction_guide_here);
       break;
+    case CodeSynthesisContext::TypeAliasTemplateInstantiation:
+      break;
     }
   }
 }
@@ -1209,6 +1255,7 @@ std::optional<TemplateDeductionInfo *> Sema::isSFINAEContext() const {
       break;
 
     case CodeSynthesisContext::Memoization:
+    case CodeSynthesisContext::TypeAliasTemplateInstantiation:
       break;
     }
 
@@ -1533,6 +1580,17 @@ namespace {
                                            SubstTemplateTypeParmPackTypeLoc TL,
                                            bool SuppressObjCLifetime);
 
+    CXXRecordDecl::LambdaDependencyKind
+    ComputeLambdaDependency(LambdaScopeInfo *LSI) {
+      auto &CCS = SemaRef.CodeSynthesisContexts.back();
+      if (CCS.Kind == Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation) {
+        unsigned TypeAliasDeclDepth = CCS.Entity->getTemplateDepth();
+        if (TypeAliasDeclDepth >= TemplateArgs.getNumSubstitutedLevels())
+          return CXXRecordDecl::LambdaDependencyKind::LDK_AlwaysDependent;
+      }
+      return inherited::ComputeLambdaDependency(LSI);
+    }
+
     ExprResult TransformLambdaExpr(LambdaExpr *E) {
       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
       Sema::ConstraintEvalRAII<TemplateInstantiator> RAII(*this);

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1083,6 +1083,11 @@ TemplateDeclInstantiator::VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D) {
     return nullptr;
 
   TypeAliasDecl *Pattern = D->getTemplatedDecl();
+  Sema::InstantiatingTemplate InstTemplate(
+      SemaRef, Pattern->getTypeSourceInfo()->getTypeLoc().getBeginLoc(), D,
+      D->getTemplateDepth() >= TemplateArgs.getNumSubstitutedLevels()
+          ? ArrayRef<TemplateArgument>()
+          : TemplateArgs.getInnermost());
 
   TypeAliasTemplateDecl *PrevAliasTemplate = nullptr;
   if (getPreviousDeclForInstantiation<TypedefNameDecl>(Pattern)) {

clang/lib/Sema/TreeTransform.h

@@ -767,6 +767,10 @@ class TreeTransform {
   /// the body.
   StmtResult SkipLambdaBody(LambdaExpr *E, Stmt *Body);
 
+  CXXRecordDecl::LambdaDependencyKind ComputeLambdaDependency(LambdaScopeInfo *LSI) {
+    return static_cast<CXXRecordDecl::LambdaDependencyKind>(LSI->Lambda->getLambdaDependencyKind());
+  }
+
   QualType TransformReferenceType(TypeLocBuilder &TLB, ReferenceTypeLoc TL);
 
   StmtResult TransformCompoundStmt(CompoundStmt *S, bool IsStmtExpr);
@@ -13936,6 +13940,11 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
                                     /*IsInstantiation*/ true);
   SavedContext.pop();
 
+  DependencyKind = getDerived().ComputeLambdaDependency(&LSICopy);
+  Class->setLambdaDependencyKind(DependencyKind);
+  Class->setTypeForDecl(nullptr);
+  getSema().Context.getTypeDeclType(Class);
+
   return getSema().BuildLambdaExpr(E->getBeginLoc(), Body.get()->getEndLoc(),
                                    &LSICopy);
 }

clang/test/SemaTemplate/alias-template-with-lambdas.cpp

@@ -0,0 +1,82 @@
+// RUN: %clang_cc1 -std=c++2c -fsyntax-only -verify %s
+namespace lambda_calls {
+
+template <class>
+concept True = true;
+
+template <class>
+concept False = false; // #False
+
+template <class T> struct S {
+  template <class... U> using type = decltype([](U...) {}(U()...));
+  template <class U> using type2 = decltype([](auto) {}(1));
+  template <class U> using type3 = decltype([](True auto) {}(1));
+  template <class>
+  using type4 = decltype([](auto... pack) { return sizeof...(pack); }(1, 2));
+
+  template <class U> using type5 = decltype([](False auto...) {}(1)); // #Type5
+
+  template <class U>
+  using type6 = decltype([]<True> {}.template operator()<char>());
+  template <class U>
+  using type7 = decltype([]<False> {}.template operator()<char>()); // #Type7
+
+  template <class U>
+  using type8 = decltype([]() // #Type8
+                           requires(sizeof(U) == 32) // #Type8-requirement
+                         {}());
+
+  template <class... U>
+  using type9 = decltype([]<True>(U...) {}.template operator()<char>(U()...));
+  // https://github.com/llvm/llvm-project/issues/76674
+  template <class U>
+  using type10 = decltype([]<class V> { return V(); }.template operator()<U>());
+
+  template <class U> using type11 = decltype([] { return U{}; });
+};
+
+template <class> using Meow = decltype([]<True> {}.template operator()<int>());
+
+template <class... U>
+using MeowMeow = decltype([]<True>(U...) {}.template operator()<char>(U()...));
+
+// https://github.com/llvm/llvm-project/issues/70601
+template <class> using U = decltype([]<True> {}.template operator()<int>());
+
+U<int> foo();
+
+void bar() {
+  using T = S<int>::type<int, int, int>;
+  using T2 = S<int>::type2<int>;
+  using T3 = S<int>::type3<char>;
+  using T4 = S<int>::type4<void>;
+  using T5 = S<int>::type5<void>; // #T5
+  // expected-error@#Type5 {{no matching function for call}}
+  // expected-note@#T5 {{type alias 'type5' requested here}}
+  // expected-note@#Type5 {{constraints not satisfied [with auto:1 = <int>]}}
+  // expected-note@#Type5 {{because 'int' does not satisfy 'False'}}
+  // expected-note@#False {{because 'false' evaluated to false}}
+
+  using T6 = S<int>::type6<void>;
+  using T7 = S<int>::type7<void>; // #T7
+  // expected-error@#Type7 {{no matching member function for call}}
+  // expected-note@#T7 {{type alias 'type7' requested here}}
+  // expected-note@#Type7 {{constraints not satisfied [with $0 = char]}}
+  // expected-note@#Type7 {{because 'char' does not satisfy 'False'}}
+  // expected-note@#False {{because 'false' evaluated to false}}
+
+  using T8 = S<int>::type8<char>; // #T8
+  // expected-error@#Type8 {{no matching function for call}}
+  // expected-note@#T8 {{type alias 'type8' requested here}}
+  // expected-note@#Type8 {{constraints not satisfied}}
+  // expected-note@#Type8-requirement {{because 'sizeof(char) == 32' (1 == 32) evaluated to false}}
+
+  using T9 = S<int>::type9<long, long, char>;
+  using T10 = S<int>::type10<int>;
+  using T11 = S<int>::type11<int>;
+  int x = T11()();
+  using T12 = Meow<int>;
+  using T13 = MeowMeow<char, int, long, unsigned>;
+}
+
+} // namespace lambda_calls