[Clang][Sema] Fix access of friend class in local class

Clang currently emits an error when a friend of a local class
tries to access it's private data members. This patch fixes the bug.

Differential Revision: https://reviews.llvm.org/D152195

clang/docs/ReleaseNotes.rst

@@ -539,6 +539,9 @@ Bug Fixes to C++ Support
 - Allow omitting ``typename`` in the parameter declaration of a friend
   constructor declaration.
   (`#63119 <https://github.com/llvm/llvm-project/issues/63119>`_)
+- Fix access of a friend class declared in a local class. Clang previously
+  emitted an error when a friend of a local class tried to access it's
+  private data members.
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDecl.cpp

@@ -17066,11 +17066,14 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       S = getTagInjectionScope(S, getLangOpts());
     } else {
       assert(TUK == TUK_Friend);
+      CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(SearchDC);
+
       // C++ [namespace.memdef]p3:
       //   If a friend declaration in a non-local class first declares a
       //   class or function, the friend class or function is a member of
       //   the innermost enclosing namespace.
-      SearchDC = SearchDC->getEnclosingNamespaceContext();
+      SearchDC = RD->isLocalClass() ? RD->isLocalClass()
+                                    : SearchDC->getEnclosingNamespaceContext();
     }
 
     // In C++, we need to do a redeclaration lookup to properly

clang/test/Sema/local-class-friend.cpp

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+// expected-no-diagnostics
+
+void foo()
+{ class c1 {
+    private:
+      int testVar;
+    public:
+      friend class c2;
+  };
+
+  class c2 {
+    void f(c1 obj) {
+      int a = obj.testVar; // Ok
+    }
+  };
+}