[llvm-branch-commits] [clang] release/19.x: [Clang] Instantiate Typedefs referenced by type alias deduction guides (#111804) (PR #112293)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/112293

Backport 0bc02b999a

Requested by: @zyn0217

>From 2717eeb2584005e08bc0b2c1b77954ff156a5bab Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Fri, 11 Oct 2024 10:31:27 +0800
Subject: [PATCH] [Clang] Instantiate Typedefs referenced by type alias
 deduction guides (#111804)

TypedefNameDecl referenced by a synthesized CTAD guide for type aliases
was not transformed previously, resulting in a substitution failure in
BuildDeductionGuideForTypeAlias() when substituting into the
right-hand-side deduction guide.

This patch fixes it in the way we have been doing since
https://reviews.llvm.org/D80743. We transform all the function
parameters, parenting referenced TypedefNameDecls with the
CXXDeductionGuideDecl. Then we instantiate these declarations in
FindInstantiatedDecl() as we build up the eventual deduction guide,
using the mechanism introduced in D80743

Fixes #111508

(cherry picked from commit 0bc02b999a9686ba240b7a68d3f1cbbf037d2170)
---
 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 0602d07c6b9b0d..1bf82b31def977 100644
--- a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
+++ b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
@@ -69,8 +69,8 @@ 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) {
@@ -1263,10 +1263,25 @@ FunctionTemplateDecl *DeclareAggregateDeductionGuideForTypeAlias(
       getRHSTemplateDeclAndArgs(SemaRef, AliasTemplate).first;
   if (!RHSTemplate)
     return nullptr;
+
+  llvm::SmallVector<TypedefNameDecl *> 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