[Bug c++/66159] bogus warning for alias-declaration using elaborated-type-specifier

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66159

--- Comment #4 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #3)
> Patch for stage 1:
> 
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index 4fa546a086c..4dc4e751b28 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -17818,9 +17818,11 @@ cp_parser_elaborated_type_specifier (cp_parser*
> parser,
>               caught elsewhere in parsing.  Those that are pointless arrive
>               here.  */
>  
> -          if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON)
> +          if (warn_redundant_decls
> +             && cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON)
>                && !is_friend && !processing_explicit_instantiation)
> -            warning (0, "declaration %qD does not declare anything", decl);
> +            warning (OPT_Wredundant_decls,
> +                    "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 5336d4ed946..f720a6cdae3 100644
> --- a/gcc/testsuite/g++.dg/warn/forward-inner.C
> +++ b/gcc/testsuite/g++.dg/warn/forward-inner.C
> @@ -1,5 +1,6 @@
>  // Check that the compiler warns about inner-style forward declarations in
>  // contexts where they're not actually illegal, but merely useless.
> +// { dg-options "-Wredundant-decls" }
>  
>  // Verify warnings for and within classes, and by extension, struct and
> union.
>  class C1;
> @@ -70,7 +71,7 @@ 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 +80,10 @@ 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;
> +#endif
> diff --git a/gcc/testsuite/g++.dg/warn/pr36999.C
> b/gcc/testsuite/g++.dg/warn/pr36999.C
> index ce2286efcf4..6f69e192d02 100644
> --- a/gcc/testsuite/g++.dg/warn/pr36999.C
> +++ b/gcc/testsuite/g++.dg/warn/pr36999.C
> @@ -1,5 +1,6 @@
>  /* PR36999: Erroneous "does not declare anything" warnings.  */
>  /* { dg-do compile } */
> +/* { dg-options "-Wredundant-decls" } */
>  
>  class C1 {
>   public: class C2 { };

It's stage 1 now.