Re: [PATCH, C] Warn ordered comparison pointer with null pointer constant

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Fri, 30 Apr 2010, Shujing Zhao wrote:

>  If
> > you also want to warn - not pedwarn, and so under -Wextra only - for ordered
> > comparisons with a pointer-type null pointer constant, I think you should do
> > so inside the case where comp_target_types has passed.
> If warn ordered comparison of pinter with null pointer, I think besides the
> void pointer with null pointer, the other pointer with null pointer need be
> warned too.

I can't make sense of what you are saying here, but this patch is also 
wrong.  By turning the

          if (comp_target_types (location, type0, type1))

into an "else if", you are losing both the errors and pedwarns if 
comp_target_types fails (for comparisons of distinct types) and those if 
it succeeds (for comparison of pointers to complete and incomplete, or of 
pointers to functions).  That is, your patch would cause cases that 
violate constraints not to get the required errors with -pedantic-errors.

As I said, put this *inside* the above conditional.  If something is more 
seriously wrong - if the types don't match and so ISO C requires a 
diagnostic - there is no need to try to give this additional optional 
diagnostic; the user will need to fix the serious problems in their 
program first before dealing with -Wextra issues.  Either make this new 
check independent of the checks inside that conditional (complete and 
incomplete, function pointers), or only give the new warning if neither of 
the previous pedwarn conditions passed.

-- 
Joseph S. Myers
joseph@codesourcery.com