Re: Revision 110444 breaks the native MS-Windows build

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 08 Oct 2012 03:20:12 -0700
> From: Daniel Colascione <dancol@dancol.org>
> CC: emacs-devel@gnu.org
> 
> > and in jconfig.h, a jpeglib header included by jpeglib.h, I see this:
> > 
> >   #ifdef _WIN32
> >   # include <windows.h>
> >   /* Define "boolean" as unsigned char, not int, per Windows custom */
> >   # if !defined __RPCNDR_H__ || defined __MINGW32__    /* don't conflict if rpcndr.h already read */
> >   #  ifndef boolean     /* don't conflict if rpcndr.h already read */
> >       typedef unsigned char boolean;
> >   #  endif /* boolean */
> >   # endif /* __RPCNDR_H__ */
> >   # define HAVE_BOOLEAN     /* prevent jmorecfg.h from redefining it */
> >   # define USE_WINDOWS_MESSAGEBOX 1
> >   #endif /* _WIN32 */
> > 
> > This seems to be in perfect order, so I don't understand the conflict
> > you were seeing.
> > 
> > In any case, you cannot hope for the above to compile unless you also
> > typedef jpeg_boolean.
> 
> My jpeglib doesn't have that code.

Which version of jpeglib is that, and where can I see its full set of
headers?  The latest upstream version, 8d, does seem to have that
code.

> The redefinition actually works fine under
> Cygwin --- the jpeglib headers there just define a type they call "boolean",
> which, thanks to our preprocessor macro, is substituted with jpeg_boolean.
> Presumably, my hack breaks native Windows because there jpeglib _doesn't_ define
> boolean.

Yes.

> I tried replacing my hack with the approach below. It does _not_ work ---
> although this patch allows Emacs to compile under both Cygwin and native
> Windows, it doesn't result in successful JPEG loading under Cygwin, presumably
> due to the ABI we've made the jpeglib headers declare no longer matching the
> compiled libjpeg we're using.

What type does jpeglib define its 'boolean' to in the Cygwin build you
have?  Or does it use Cygwin's own 'boolean'? if so, what is its width?

FWIW, I've just configured the latest jpeglib for MinGW, and the above
conditional definition did appear in jconfig.h that was created.

In any case, this sounds like a problem someone should report
upstream: a Cygwin application using jpeglib could definitely include
Windows headers, can't it?  If jpeglib configured for Cygwin doesn't
include the above conditional, then it will cause bugs on Cygwin, I
think.

> Instead, let's do this:
> 
> +/* rpcndr.h (via windows.h) and jpeglib.h both define boolean types.
> +   Some versions of jpeglib try to detect whether rpcndr.h is loaded,
> +   using the Windows boolean type instead of the jpeglib boolean type
> +   if so.  Cygwin jpeglib, however, doesn't try to detect whether its
> +   headers are included along with windows.h, so under Cygwin, jpeglib
> +   attempts to define a conflicting boolean type.  Worse, forcing
> +   Cygwin jpeglib headers to use the Windows boolean type doesn't work
> +   because it created an ABI incompatibility between the
> +   already-compiled jpeg library and the header interface definition.
> +
> +   The best we can do is to define jpeglib's boolean type to a
> +   different name.  This name, jpeg_boolean, remains in effect through
> +   the rest of image.c.
> +*/
> +#if defined (CYGWIN) && defined (HAVE_NTGUI)
>  #define boolean jpeg_boolean
> +#endif
>  #include <jpeglib.h>
>  #include <jerror.h>

That could be fine, but I'd like to understand the problem some more,
because the problem you had could be specific to some version of
jpeglib, and if so, this change could break with other versions or on
other Cygwin installations.

Thanks.