[Clang] Fix access of friend function in local class

[eandrews]

Summary

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.

[erichkeane]

I think the patch looks fine, but this needs a release note.

[eandrews]

In D152195#4399251, @erichkeane wrote:

I think the patch looks fine, but this needs a release note.

Just so I know - Does every bug fix need a release note now?

[erichkeane]

In D152195#4399445, @eandrews wrote:

In D152195#4399251, @erichkeane wrote:

I think the patch looks fine, but this needs a release note.

Just so I know - Does every bug fix need a release note now?

Just about every commit we expect to have a release note unless it is fixing a regression introduced since the last release, or is NFC. So yes, every bug fix should have one. If possible, add a link to the github issue (if it doesn't exist, obviously you don't have to).

[eandrews]

Thanks for the review! I added a release note

clang/docs/ReleaseNotes.rst

- Some predefined expressions are now treated as string literals in MSVC
   (`#114 <https://github.com/llvm/llvm-project/issues/114>`_)
 - Fix parsing of `auto(x)`, when it is surrounded by parentheses.
   (`#62494 <https://github.com/llvm/llvm-project/issues/62494>`_)
 - Fix handling of generic lambda used as template arguments.
   (`#62611 <https://github.com/llvm/llvm-project/issues/62611>`_)
 - 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
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 - Preserve ``namespace`` definitions that follow malformed declarations.
 
 Miscellaneous Bug Fixes
 ^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDecl.cpp

if (TUK == TUK_Reference || IsTemplateParamOrArg) {
       // FIXME: We would like to maintain the current DeclContext as the
       // lexical context,
       SearchDC = getTagInjectionContext(SearchDC);
 
       // Find the scope where we'll be declaring the tag.
       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
     // diagnose some problems.
     // FIXME: redeclaration lookup is also used (with and without C++) to find a
     // hidden declaration so that we don't get ambiguity errors when using a
     // type declared by an elaborated-type-specifier.  In C that is not correct
     // and we should instead merge compatible types found by lookup.

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

+// 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
+    }
+  };
+}