BUG: gtk+ 2.8.17 GDK_IS_PIXBUF macro.

["John E. Malmberg" <wb8tyw qsl net>]

It looks to me like there is a bug in the GDK_IS_xxxxx(object) macros, 
and probably in the GDK_xxxxx(object) macros.

These macros always invoke a GDK_TYPE_xxxxx macro as their last step 
which calls a routine gdk_xxxxx_get_type();

Example from gdk-pixbuf/gdk-pixbuf-core.h (reformatted)

#define GDK_TYPE_PIXBUF         (gdk_pixbuf_get_type ())
#define GDK_PIXBUF(object)    \
 (G_TYPE_CHECK_INSTANCE_CAST ((object), GDK_TYPE_PIXBUF, GdkPixbuf))
#define GDK_IS_PIXBUF(object)  \
 (G_TYPE_CHECK_INSTANCE_TYPE ((object), GDK_TYPE_PIXBUF))


If the type already exists, as in the case where the dynamically loaded 
images libpixbufloader-nnnn are used, then the GDK_IS_xxxxx macro will 
fail with the following visible diagnostics:

(process:1336004): GLib-GObject-WARNING **: cannot register existing 
type `GdkPixbuf'

(process:1336004): GdkPixbuf-CRITICAL **: file 
SRC_ROOT:[gtk^+-2^.8^.17.gdk-pixbuf]gdk-pixdata.c;1: line 323: assertion 
`GDK_IS_PIXBUF (pixbuf)' failed

It looks like these macros should only be invoking the GDK_TYPE_xxxxx 
macros if the first call to G_TYPE_CHECK_INSTANCE_nnnn() fails.

Either that, or the gdk_xxxxx_get_type() routines need to be able to 
handle that a type may already have been registered, since there seems 
to be two different ways of registering the PIXBUF and related types.

This is affecting the generation of two files in the build:

  gtk/stock-icons/gtkstockpixbufs.h
  demos/test-inline-pixbufs.h

The failure to generate the first file is not stopping the build because
it is also supplied in the tarball for gtk+ 2.8.7.  The second one 
failing is preventing the demos directory from being built, and some of 
the test or demo programs are failing with the same diagnostic above.

I am looking for some recommendations on what to do to get this to work 
correctly.  The obvious thing that looks like it would make the affected 
programs work would be to remove the GDK_TYPE_PIXBUF invocation from the 
GDK_IS_PIXBUF macro, or to only invoke it if the 
G_TYPE_INSTANCE_TYPE(object) call fails.

It looks like the intent of these macros was to register the type if it 
was not already registered, and only fail if the type was not registered 
and could not be registered.

-John
wb8tyw qsl net
Personal Opinion Only