Re: [PATCH] Fix compilation erorr when --enable-gcc-warnings passed

[Alexander Kuleshov <kuleshovmail@gmail.com>]

Hello Paul,

On 01-22-16, Paul Eggert wrote:
> On 01/22/2016 02:54 AM, Alexander Kuleshov wrote:
> >@@ -4615,16 +4622,15 @@ colors_in_color_table (int *n)
> >  static unsigned long
> >  lookup_rgb_color (struct frame *f, int r, int g, int b)
> >  {
> >-  unsigned long pixel;
> >-
> >  #ifdef HAVE_NTGUI
> >-  pixel = PALETTERGB (r >> 8, g >> 8, b >> 8);
> >+  return PALETTERGB (r >> 8, g >> 8, b >> 8);
> >  #endif /* HAVE_NTGUI */
> >  #ifdef HAVE_NS
> >-  pixel = RGB_TO_ULONG (r >> 8, g >> 8, b >> 8);
> >+  return RGB_TO_ULONG (r >> 8, g >> 8, b >> 8);
> >  #endif /* HAVE_NS */
> >-  return pixel;
> >+
> >+  return 0;
> >  }
> 
> Does this change cause lookup_rgb_color to always return 0 on platforms
> other than MS-Windows and NextStep? Is this the right thing to do? This part
> of the change isn't mentioned in the draft ChangeLog entry, so I'm a bit
> lost as to the motivation.

Some motivation: Previous version was:

static unsigned long
lookup_rgb_color (struct frame *f, int r, int g, int b)
{
  unsigned long pixel;

#ifdef HAVE_NTGUI
  pixel = PALETTERGB (r >> 8, g >> 8, b >> 8);
#endif /* HAVE_NTGUI */

#ifdef HAVE_NS
  pixel = RGB_TO_ULONG (r >> 8, g >> 8, b >> 8);
#endif /* HAVE_NS */
  return pixel;
}

So, during compilation with enabled warnings, we will get following
error:

image.c: In function ‘lookup_rgb_color’:
image.c:4634:10: error: ‘pixel’ is used uninitialized in this function [-Werror=uninitialized]
   return pixel;

And seems that this version of the lookup_rgb_color() is only for these platforms, because I see that the src/image.c contains yet another implementation of the lookup_rgb_color() for platforms where COLOR_TABLE_SUPPORT is enabled.