Re: [PATCH] Fix description of Wendif-labels (PR documentation/78732)

[Martin Sebor <msebor at gmail dot com>]

On 03/31/2017 09:06 AM, David Malcolm wrote:
> As noted in the PR, c.opt's description of -Wendif-labels erroneously
> refers to #elif, rather than #else.
>
> warn_endif_labels is used by:
>   libcpp/directives.c: do_else
>   libcpp/directives.c: do_endif
> in which they use it to guard calls to check_eol_endif_labels.
>
> It's not used by do_elif.

Presumably it should to have GCC warn on the extra tokens after
the constant expression in the #elif directive just as warns about
those after the #else:

  #if 1
  #elif 1 foo bar
  #else if 1 foobar
  #endif baz
  a.c:3:7: warning: extra tokens at end of #else directive [-Wendif-labels]
   #else if 1 foobar
         ^~
  a.c:4:8: warning: extra tokens at end of #endif directive 
[-Wendif-labels]
   #endif baz
          ^~~
  a.c:4:0: warning: ISO C forbids an empty translation unit [-Wpedantic]
 #endif baz

Martin

> doc/cppwarnopts.texi gets this right:
>
> > Do not warn whenever an @code{#else} or an @code{#endif} are followed by text.
> > This sometimes happens in older programs with code of the form
>
> This patch fixes the description in c.opt.
>
> Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu.
>
> Committed to trunk as obvious (r246616).
>
> gcc/c-family/ChangeLog:
> 	PR documentation/78732
> 	* c.opt (Wendif-labels): Fix description to refer to
> 	#else rather than #elif.
> ---
>  gcc/c-family/c.opt | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 78fea61..13b930d 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -486,7 +486,7 @@ Warn about an empty body in an if or else statement.
>
>  Wendif-labels
>  C ObjC C++ ObjC++ CPP(warn_endif_labels) CppReason(CPP_W_ENDIF_LABELS) Var(cpp_warn_endif_labels) Init(1) Warning LangEnabledBy(C ObjC C++ ObjC++,Wpedantic)
> -Warn about stray tokens after #elif and #endif.
> +Warn about stray tokens after #else and #endif.
>
>  Wenum-compare
>  C ObjC C++ ObjC++ Var(warn_enum_compare) Init(-1) Warning LangEnabledBy(C ObjC,Wall || Wc++-compat)