[clang] [Clang] Instantiate Typedefs referenced by type alias deduction guides (PR #111804)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 created https://github.com/llvm/llvm-project/pull/111804

Fixes #111508 

>From 1319a3c3220df06f5436fd3f135e50c998940296 Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Thu, 10 Oct 2024 16:40:10 +0800
Subject: [PATCH] [Clang] Instantiate Typedefs referenced by type alias
 deduction guides

---
 clang/lib/Sema/SemaTemplateDeductionGuide.cpp | 21 ++++++++++++++++---
 clang/test/SemaCXX/cxx20-ctad-type-alias.cpp  | 13 ++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
index ca93c840f03215..871c705ab65421 100644
--- a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
+++ b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
@@ -70,8 +70,8 @@ class ExtractTypeForDeductionGuide
   ExtractTypeForDeductionGuide(
       Sema &SemaRef,
       llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs,
-      ClassTemplateDecl *NestedPattern,
-      const MultiLevelTemplateArgumentList *OuterInstantiationArgs)
+      ClassTemplateDecl *NestedPattern = nullptr,
+      const MultiLevelTemplateArgumentList *OuterInstantiationArgs = nullptr)
       : Base(SemaRef), MaterializedTypedefs(MaterializedTypedefs),
         NestedPattern(NestedPattern),
         OuterInstantiationArgs(OuterInstantiationArgs) {
@@ -1215,10 +1215,25 @@ FunctionTemplateDecl *DeclareAggregateDeductionGuideForTypeAlias(
       getRHSTemplateDeclAndArgs(SemaRef, AliasTemplate).first;
   if (!RHSTemplate)
     return nullptr;
+
+  llvm::SmallVector<TypedefNameDecl *, 4> TypedefDecls;
+  llvm::SmallVector<QualType> NewParamTypes;
+  ExtractTypeForDeductionGuide TypeAliasTransformer(SemaRef, TypedefDecls);
+  for (QualType P : ParamTypes) {
+    QualType Type = TypeAliasTransformer.TransformType(P);
+    if (Type.isNull())
+      return nullptr;
+    NewParamTypes.push_back(Type);
+  }
+
   auto *RHSDeductionGuide = SemaRef.DeclareAggregateDeductionGuideFromInitList(
-      RHSTemplate, ParamTypes, Loc);
+      RHSTemplate, NewParamTypes, Loc);
   if (!RHSDeductionGuide)
     return nullptr;
+
+  for (TypedefNameDecl *TD : TypedefDecls)
+    TD->setDeclContext(RHSDeductionGuide->getTemplatedDecl());
+
   return BuildDeductionGuideForTypeAlias(SemaRef, AliasTemplate,
                                          RHSDeductionGuide, Loc);
 }
diff --git a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
index 5392573fcdb9d5..675c32a81f1ae8 100644
--- a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
+++ b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
@@ -481,3 +481,16 @@ struct Out {
 Out<float>::B out(100); // deduced to Out<float>::A<float>;
 static_assert(__is_same(decltype(out), Out<float>::A<float>));
 }
+
+namespace GH111508 {
+
+template <typename V> struct S {
+  using T = V;
+  T Data;
+};
+
+template <typename V> using Alias = S<V>;
+
+Alias A(42);
+
+} // namespace GH111508