Re: [PATCH v2] cpp/c: Add -Wexpansion-to-defined

[Paolo Bonzini <bonzini@gnu.org>]

On 10/08/2016 17:33, Joseph Myers wrote:
> On Wed, 10 Aug 2016, Paolo Bonzini wrote:
> 
>> - stuff that is not enabled by anything should use OPT_Wpedantic, and
> 
> No, lots of pedwarns are for usages that are (a) dubious enough we want to 
> diagnose them by default, and (b) required to be diagnosed by ISO C so 
> must become errors with -pedantic-errors.  (You could argue about whether 
> we should have -fpermissive for C like for C++ and make some of those into 
> errors by default.)

There are indeed many pedwarn(loc, 0, ...) occurrences in C++ (most, but
not all, are "foo only available with -std=bar" which in the C front-end
would use OPT_Wpedantic, OPT_W*compat be enabled by specific flags such
as -Wvariadic-macros).  In C I only see three:

- overflowing floating-point constants:

          if (!MODE_HAS_INFINITIES (TYPE_MODE (type)))
            pedwarn (input_location, 0,
                     "floating constant exceeds range of %qT", type);
          else
            warning (OPT_Woverflow,
                     "floating constant exceeds range of %qT", type);

- __FUNCTION__ outside function scope

  if (!ix && !current_function_decl)
    pedwarn (loc, 0, "%qD is not defined outside of function scope", decl);

- macro redefinition

For the first two it would not feel wrong at all to use permerror.  The
last one indeed is a very good example of a pedwarn.

Paolo