c++: Fix bogus "does not declare anything" warning (PR 66159)

G++ gives a bogus warning for 'struct A; using B = struct ::A;'
complaining that the elaborated-type-specifier doesn't declare anything.
That's true, but it's not trying to declare struct ::A, just refer to it
unambiguously. Do not emit the warning unless we're actually parsing a
declaration.

gcc/cp/ChangeLog:

	PR c++/66159
	* parser.c (cp_parser_elaborated_type_specifier): Do not warn
	unless in a declaration.

gcc/testsuite/ChangeLog:

	PR c++/66159
	* g++.dg/warn/forward-inner.C: Check alias-declaration using
	elaborated-type-specifier.

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 69839baa7123e2a2a2295204bb65386f9fb35f51..815582c825eeb8765c1abe0991d6af15a68df28c 100644 (file)
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -18953,7 +18953,8 @@ cp_parser_elaborated_type_specifier (cp_parser* parser,
              here.  */
 
           if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON)
-              && !is_friend && !processing_explicit_instantiation)
+             && !is_friend && is_declaration
+             && !processing_explicit_instantiation)
             warning (0, "declaration %qD does not declare anything", decl);
 
          type = TREE_TYPE (decl);

diff --git a/gcc/testsuite/g++.dg/warn/forward-inner.C b/gcc/testsuite/g++.dg/warn/forward-inner.C
index 5336d4ed946191fd13767f8858cfd2185ec47a71..d7b93f8ad0804930cea5493eb8296a046f8849af 100644 (file)
--- a/gcc/testsuite/g++.dg/warn/forward-inner.C
+++ b/gcc/testsuite/g++.dg/warn/forward-inner.C
@@ -70,7 +70,7 @@ template class TC6<int>::TC7;  // Valid explicit instantiation, no warning
 
 
 // Verify that friend declarations, also easy to confuse with forward
-// declrations, are similarly not warned about.
+// declarations, are similarly not warned about.
 class C8 {
  public:
   class C9 { };
@@ -79,3 +79,10 @@ class C10 {
  public:
   friend class C8::C9;         // Valid friend declaration, no warning
 };
+
+#if __cplusplus >= 201103L
+// Verify that alias-declarations using an elaborated-type-specifier and
+// nested-name-specifier are not warned about (PR c++/66159).
+struct C11;
+using A1 = struct ::C11; // Valid alias-decl, no warning
+#endif