[C++20][Modules] Number the anonymous members if the decl was instantiated locally.

mpark · mpark · commit c9f95c168f0a · 2025-09-12T21:15:58.000-07:00
diff --git a/clang/include/clang/AST/DeclTemplate.h b/clang/include/clang/AST/DeclTemplate.h
@@ -1874,6 +1874,13 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
   LLVM_PREFERRED_TYPE(bool)
   unsigned StrictPackMatch : 1;
 
+  /// Indicate whether this template was instantiated, and instantiated locally.
+  /// Specifically, this is false if the template has not been instantiated,
+  /// or was intantiated externally and loaded via an AST file. This only tracks
+  /// class template specializations for proper handling of anonymous members.
+  LLVM_PREFERRED_TYPE(bool)
+  unsigned InstantiatedLocally : 1;
+
 protected:
   ClassTemplateSpecializationDecl(ASTContext &Context, Kind DK, TagKind TK,
                                   DeclContext *DC, SourceLocation StartLoc,
@@ -1968,6 +1975,10 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
 
   void setStrictPackMatch(bool Val) { StrictPackMatch = Val; }
 
+  bool isInstantiatedLocally() { return InstantiatedLocally; }
+
+  void setInstantiatedLocally() { InstantiatedLocally = true; }
+
   /// Get the point of instantiation (if any), or null if none.
   SourceLocation getPointOfInstantiation() const {
     return PointOfInstantiation;
diff --git a/clang/lib/AST/DeclTemplate.cpp b/clang/lib/AST/DeclTemplate.cpp
@@ -974,15 +974,16 @@ ClassTemplateSpecializationDecl::ClassTemplateSpecializationDecl(
                     SpecializedTemplate->getIdentifier(), PrevDecl),
       SpecializedTemplate(SpecializedTemplate),
       TemplateArgs(TemplateArgumentList::CreateCopy(Context, Args)),
-      SpecializationKind(TSK_Undeclared), StrictPackMatch(StrictPackMatch) {
+      SpecializationKind(TSK_Undeclared), StrictPackMatch(StrictPackMatch),
+      InstantiatedLocally(false) {
   assert(DK == Kind::ClassTemplateSpecialization || StrictPackMatch == false);
 }
 
 ClassTemplateSpecializationDecl::ClassTemplateSpecializationDecl(ASTContext &C,
                                                                  Kind DK)
     : CXXRecordDecl(DK, TagTypeKind::Struct, C, nullptr, SourceLocation(),
                     SourceLocation(), nullptr, nullptr),
-      SpecializationKind(TSK_Undeclared) {}
+      SpecializationKind(TSK_Undeclared), InstantiatedLocally(false)  {}
 
 ClassTemplateSpecializationDecl *ClassTemplateSpecializationDecl::Create(
     ASTContext &Context, TagKind TK, DeclContext *DC, SourceLocation StartLoc,
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -3699,6 +3699,7 @@ Sema::InstantiateClass(SourceLocation PointOfInstantiation,
         = dyn_cast<ClassTemplateSpecializationDecl>(Instantiation)) {
     Spec->setTemplateSpecializationKind(TSK);
     Spec->setPointOfInstantiation(PointOfInstantiation);
+    Spec->setInstantiatedLocally();
   }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -3425,7 +3425,16 @@ NamedDecl *ASTDeclReader::getAnonymousDeclForMerging(ASTReader &Reader,
   // If this is the first time, but we have parsed a declaration of the context,
   // build the anonymous declaration list from the parsed declaration.
   auto *PrimaryDC = getPrimaryDCForAnonymousDecl(DC);
-  if (PrimaryDC && !cast<Decl>(PrimaryDC)->isFromASTFile()) {
+  auto needToNumberAnonymousDeclsWithin = [](Decl *D) {
+    if (!D->isFromASTFile())
+      return true;
+    // If this is a class template specialization from an AST file
+    // but the instantiation occurred locally, we still need to number
+    // the anonymous decls.
+    auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(D);
+    return CTSD && CTSD->isInstantiatedLocally();
+  };
+  if (PrimaryDC && needToNumberAnonymousDeclsWithin(cast<Decl>(PrimaryDC))) {
     numberAnonymousDeclsWithin(PrimaryDC, [&](NamedDecl *ND, unsigned Number) {
       if (Previous.size() == Number)
         Previous.push_back(cast<NamedDecl>(ND->getCanonicalDecl()));

Original file line number	Diff line number	Diff line change
`@@ -3699,6 +3699,7 @@ Sema::InstantiateClass(SourceLocation PointOfInstantiation,`
`3699`	`3699`	`= dyn_cast<ClassTemplateSpecializationDecl>(Instantiation)) {`
`3700`	`3700`	`Spec->setTemplateSpecializationKind(TSK);`
`3701`	`3701`	`Spec->setPointOfInstantiation(PointOfInstantiation);`
	`3702`	`+ Spec->setInstantiatedLocally();`
`3702`	`3703`	`}`
`3703`	`3704`
`3704`	`3705`	`InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);`