[clang] [Clang] Fix name lookup for dependent bases (PR #114978)

[Vladislav Belov via cfe-commits]

https://github.com/vbe-sc updated https://github.com/llvm/llvm-project/pull/114978

>From 11c24e5592bfdf8849bb415580d37a6f545e4952 Mon Sep 17 00:00:00 2001
From: vb-sc <vladislav.belov at syntacore.com>
Date: Tue, 5 Nov 2024 15:46:57 +0300
Subject: [PATCH] [clang] Fix name lookup for dependent bases

---
 clang/lib/AST/CXXInheritance.cpp | 14 ++++++----
 clang/test/CXX/drs/cwg5xx.cpp    | 48 ++++++++++++++++++++++++++++++--
 2 files changed, 55 insertions(+), 7 deletions(-)

diff --git a/clang/lib/AST/CXXInheritance.cpp b/clang/lib/AST/CXXInheritance.cpp
index eb265a872c1259..b2e77037c10c72 100644
--- a/clang/lib/AST/CXXInheritance.cpp
+++ b/clang/lib/AST/CXXInheritance.cpp
@@ -170,13 +170,19 @@ bool CXXBasePaths::lookupInBases(ASTContext &Context,
     QualType BaseType =
         Context.getCanonicalType(BaseSpec.getType()).getUnqualifiedType();
 
+    bool isCurrentInstantiation = false;
+    if (auto *BaseRecord =
+            cast<CXXRecordDecl>(BaseSpec.getType()->getAsRecordDecl()))
+      isCurrentInstantiation = BaseRecord->isDependentContext() &&
+                               BaseRecord->isCurrentInstantiation(Record);
     // C++ [temp.dep]p3:
     //   In the definition of a class template or a member of a class template,
     //   if a base class of the class template depends on a template-parameter,
     //   the base class scope is not examined during unqualified name lookup
     //   either at the point of definition of the class template or member or
     //   during an instantiation of the class tem- plate or member.
-    if (!LookupInDependent && BaseType->isDependentType())
+    if (!LookupInDependent &&
+        (BaseType->isDependentType() && !isCurrentInstantiation))
       continue;
 
     // Determine whether we need to visit this base class at all,
@@ -244,9 +250,8 @@ bool CXXBasePaths::lookupInBases(ASTContext &Context,
         return FoundPath;
       }
     } else if (VisitBase) {
-      CXXRecordDecl *BaseRecord;
+      CXXRecordDecl *BaseRecord = nullptr;
       if (LookupInDependent) {
-        BaseRecord = nullptr;
         const TemplateSpecializationType *TST =
             BaseSpec.getType()->getAs<TemplateSpecializationType>();
         if (!TST) {
@@ -265,8 +270,7 @@ bool CXXBasePaths::lookupInBases(ASTContext &Context,
             BaseRecord = nullptr;
         }
       } else {
-        BaseRecord = cast<CXXRecordDecl>(
-            BaseSpec.getType()->castAs<RecordType>()->getDecl());
+        BaseRecord = cast<CXXRecordDecl>(BaseSpec.getType()->getAsRecordDecl());
       }
       if (BaseRecord &&
           lookupInBases(Context, BaseRecord, BaseMatches, LookupInDependent)) {
diff --git a/clang/test/CXX/drs/cwg5xx.cpp b/clang/test/CXX/drs/cwg5xx.cpp
index ed0c7159dfc889..0d53a9d07d76de 100644
--- a/clang/test/CXX/drs/cwg5xx.cpp
+++ b/clang/test/CXX/drs/cwg5xx.cpp
@@ -1178,17 +1178,61 @@ namespace cwg590 { // cwg590: yes
   template<typename T> typename A<T>::B::C A<T>::B::C::f(A<T>::B::C) {}
 }
 
-namespace cwg591 { // cwg591: no
+namespace cwg591 { // cwg591: yes
   template<typename T> struct A {
     typedef int M;
     struct B {
       typedef void M;
       struct C;
+      struct D;
+    };
+  };
+
+  template<typename T> struct G {
+    struct B {
+      typedef int M;
+      struct C {
+        typedef void M;
+        struct D;
+      };
+    };
+  };
+
+  template<typename T> struct H {
+    template<typename U> struct B {
+      typedef int M;
+      template<typename F> struct C {
+        typedef void M;
+        struct D;
+        struct P;
+      };
     };
   };
 
   template<typename T> struct A<T>::B::C : A<T> {
-    // FIXME: Should find member of non-dependent base class A<T>.
+    M m;
+  };
+
+  template<typename T> struct G<T>::B::C::D : B {
+    M m;
+  };
+
+  template<typename T>
+  template<typename U>
+  template<typename F>
+  struct H<T>::B<U>::C<F>::D : B<U> {
+    M m;
+  };
+
+  template<typename T> struct A<T>::B::D : A<T*> {
+    M m;
+    // expected-error at -1 {{field has incomplete type 'M' (aka 'void'}}
+  };
+
+  template<typename T>
+  template<typename U>
+  template<typename F>
+  struct H<T>::B<U>::C<F>::P : B<F> {
     M m;
     // expected-error at -1 {{field has incomplete type 'M' (aka 'void'}}
   };