Fix scope of typedefs present inside a template class (llvm#146729)

When a typedef is declared within a templated class, clang incorrectly
assigns the typedef to the compilation unit (CU) scope rather than the
intended scope of the templated class. This issue arises because, during
the creation of the typedef, the context lookup in the RegionMap fails
to locate the templated class, despite its prior creation.
The problem stems from the way the context is stored in the RegionMap.
When handling templated types, the current implementation stores the
class specialization rather than the templated declaration itself. This
leads to a mismatch when attempting to retrieve the context for the
typedef.
To address this issue, the solution involves modifying the
CreatedLimitedType() function. Specifically, when a struct or class is a
templated type, we should store the actual templated declaration in the
RegionMap instead of the class specialization. This ensures that
subsequent lookups for context, such as those needed for typedef
declarations, correctly identify the templated class scope.
Fixes llvm#91451

Author: ykhatav

clang/docs/ReleaseNotes.rst

@@ -229,6 +229,7 @@ Bug Fixes in This Version
   cast chain. (#GH149967).
 - Fixed a crash with incompatible pointer to integer conversions in designated
   initializers involving string literals. (#GH154046)
+- Fixed scope of typedefs present inside a template class. (#GH91451)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -4184,7 +4184,14 @@ llvm::DICompositeType *CGDebugInfo::CreateLimitedType(const RecordType *Ty) {
     break;
   }
 
-  RegionMap[RD].reset(RealDecl);
+  if (auto *CTSD =
+          dyn_cast<ClassTemplateSpecializationDecl>(Ty->getOriginalDecl())) {
+    CXXRecordDecl *TemplateDecl =
+        CTSD->getSpecializedTemplate()->getTemplatedDecl();
+    RegionMap[TemplateDecl].reset(RealDecl);
+  } else {
+    RegionMap[RD].reset(RealDecl);
+  }
   TypeCache[QualType(Ty, 0).getAsOpaquePtr()].reset(RealDecl);
 
   if (const auto *TSpecial = dyn_cast<ClassTemplateSpecializationDecl>(RD))

clang/test/DebugInfo/CXX/dependent-template-type-scope.cpp

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -debug-info-kind=standalone  -o - %s | FileCheck %s
+
+template <typename T = int>
+struct Y {
+  typedef int outside;
+  outside o;
+};
+
+Y<> y;
+
+// CHECK: ![[Y:.*]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Y<int>", {{.*}}identifier: "_ZTS1YIiE")
+// CHECK: !DIDerivedType(tag: DW_TAG_typedef, name: "outside", scope: ![[Y]],