[Bug c++/113760] [DR1693] gcc rejects valid empty-declaration in pedantic mode

["mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113760

--- Comment #8 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #7)
> g++ emits 4 errors on
> struct S
> {
>   void foo () {}
>   void bar () {};
>   void baz () = delete;
>   void qux () = delete;
>   ;
>   void corge () = delete;
>   ;
>   ;
>   int s;
>   ;
> };
> ;
> ;
> (one after qux, 2 after corge, one after s), clang++ -pedantic-errors
> -std=c++23 including trunk 2 (one after corge, one after s), so neither
> implements the DR.  Strangely, with -pedantic-errors -std=c++23 -Wextra-semi
> it warns 7 times but doesn't error (which is I think the desirable state).
> Now, g++ with -pedantic-errors -std=c++23 -Wextra-semi emits just one
> warning on the ; after bar and still the 4 errors.
> 
> That said, -Wextra-semi in GCC is documented that way:
>      Warn about redundant semicolons after in-class function
>      definitions.
> and clang doesn't bother to document it at all (at least haven't found it).
> 
> So, shall we change documentation of -Wextra-semi and say change
>       /* A declaration consisting of a single semicolon is invalid
>        * before C++11.  Allow it unless we're being pedantic.  */
>       if (cxx_dialect < cxx11)
>         pedwarn (input_location, OPT_Wpedantic, "extra %<;%>");
> to else warning (OPT_Wextra_semi, "extra %<;%>"); etc.?

Yeah, I'd say so.

> Then there is
>           if (!in_system_header_at (token->location))
>             {
>               gcc_rich_location richloc (token->location);
>               richloc.add_fixit_remove ();
>               pedwarn (&richloc, OPT_Wpedantic, "extra %<;%>");
>             }
> should that be similarly if (cxx_dialect < cxx11) pedwarn; else warning ?

I think so.  The < cxx11 is definitely missing here.

> Or, if we want to change this already for GCC 14, do that if (cxx_dialect <
> cxx11) part
> just before the last pedwarn above and add the else warning for GCC 15?

I would do it all at once.

I guess:

{} -> no warnings in any dialect
-pedantic -> pedwarns only in C++03
-Wextra-semi -> all warnings in all dialects
-std=c++11 -pedantic -Wextra-semi -> only -Wextra-semi warnings
-std=c++03 -pedantic -Wextra-semi -> pedwarns
-std=c++11 -pedantic -Wno-extra-semi -> no warnings
-std=c++03 -pedantic -Wno-extra-semi -> no warnings
-std=c++03 -pedantic-errors -Wextra-semi -> errors (?)
-std=c++11 -pedantic-errors -Wextra-semi -> warnings