[Bug c++/86733] c++17 and #pragma GCC diagnostic warning "-Wall" resurrect pre-c++11 warnings.

[Emmanuel.Thome at inria dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86733

--- Comment #2 from Emmanuel Thomé <Emmanuel.Thome at inria dot fr> ---
(In reply to Jonathan Wakely from comment #1)
> Presumably the handling for the pragma just turns the option on without
> considering the current cxx_dialect.

It seems to me that it is not consistent with the test case compiling fine with
g++ -std=c++11 -c foo.cpp , is it ?

> This should fix it:
> 
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -9210,7 +9210,7 @@ cp_parser_binary_expression (cp_parser* parser, bool
> cast_p,
>        /* Get an operator token.  */
>        token = cp_lexer_peek_token (parser->lexer);
>  
> -      if (warn_cxx11_compat
> +      if (warn_cxx11_compat && cxx_dialect < cxx11
>            && token->type == CPP_RSHIFT
>            && !parser->greater_than_is_operator_p)
>          {

Yes it does.

However, when reading gcc/c-family/c-opts.c one surmises that there is an
intent to disable warn_cxx11_compat altogether if cxx_dialect >= cxx11 ; this
code path is apparently not walked when warnings are enabled with #pragma,
which (I presume) sets -Wall only based on EnabledBy and LangEnabledBy in
c.opt, unconditionally.

Maybe there are other bugs in the same vein, then (insofar as "warning X is
enabled by -Wall [or -Wextra] in [dialect XYZ]" is often implemented in
c-opts.c, and would then be missed by the #pragma).