can you give some examples in gtk headers where this would be relevant ?
(asking about headers because I don't really care if gtk+ itself is free of such warnings)

It breaks compilation of _other_ software using -Werror -Wc++-compat, such as Wireshark.
Thanks to the presence of this we can't use -Wc++-compat in GTK+ related part.

 could you provide some logs that show examples of the breakage, please ?

Created attachment 271606 [details] [review]
the patch

that's not what Matthias asked.

also, that "and" goes into an attribute text field, not in a compilation unit, so it should never trigger a c++-compat warning. on top of that, the whole header is conditionally dependent on an `extern "C" { }` block.

can you please attach a compilation log?

On Debian testing (GTK+ 3.10)

$ echo -e '#include <gtk/gtk.h>\nmain(){};' > test.c
$ gcc -I $(pkg-config --cflags gtk+-3.0) $(pkg-config --cflags glib-2.0) -Werror -Wc++-compat test.c
In file included from /usr/include/gtk-3.0/gtk/gtkapplication.h:27:0,
                 from /usr/include/gtk-3.0/gtk/gtkwindow.h:33,
                 from /usr/include/gtk-3.0/gtk/gtkdialog.h:33,
                 from /usr/include/gtk-3.0/gtk/gtkaboutdialog.h:30,
                 from /usr/include/gtk-3.0/gtk/gtk.h:31,
                 from test.c:1:
/usr/include/gtk-3.0/gtk/gtkwidget.h:945:58: error: identifier "and" is a special operator name in C++ [-Werror=c++-compat]
 GDK_DEPRECATED_IN_3_0_FOR(gtk_widget_get_preferred_width and gtk_widget_get_preferred_height)
                                                          ^
cc1: all warnings being treated as errors

@Emmanuele: It was clear what Matthias asked, I just noticed that I forgot adding the patch for this second bug report.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40564 seems related

Thank you for fixing that. The fix may also be a good candidate for back-porting to 3.10.x IMHO.