Cannot compile programs that use gtk.h and -Werror

[Dan Kegel]

To reproduce:

sudo apt install libgtk2.0-dev && echo "#include <gtk/gtk.h>" > foo.c && gcc -Werror -c foo.c $(pkg-config --cflags gtk+-2.0) || echo FAIL

Should complete silently and produce foo.o, but instead, fails as follows:

Reading package lists... Done
Building dependency tree
Reading state information... Done
libgtk2.0-dev is already the newest version (2.24.32-4ubuntu1).
libgtk2.0-dev set to manually installed.
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
In file included from /usr/include/gtk-2.0/gtk/gtkobject.h:37,
                 from /usr/include/gtk-2.0/gtk/gtkwidget.h:36,
                 from /usr/include/gtk-2.0/gtk/gtkcontainer.h:35,
                 from /usr/include/gtk-2.0/gtk/gtkbin.h:35,
                 from /usr/include/gtk-2.0/gtk/gtkwindow.h:36,
                 from /usr/include/gtk-2.0/gtk/gtkdialog.h:35,
                 from /usr/include/gtk-2.0/gtk/gtkaboutdialog.h:32,
                 from /usr/include/gtk-2.0/gtk/gtk.h:33,
                 from foo.c:1:
/usr/include/gtk-2.0/gtk/gtktypeutils.h:236:1: error: ‘GTypeDebugFlags’ is deprecated [-Werror=deprecated-declarations]
  236 | void gtk_type_init (GTypeDebugFlags debug_flags);
      | ^~~~
In file included from /usr/include/glib-2.0/gobject/gobject.h:24,
                 from /usr/include/glib-2.0/gobject/gbinding.h:29,
                 from /usr/include/glib-2.0/glib-object.h:23,
                 from /usr/include/glib-2.0/gio/gioenums.h:28,
                 from /usr/include/glib-2.0/gio/giotypes.h:28,
                 from /usr/include/glib-2.0/gio/gio.h:26,
                 from /usr/include/gtk-2.0/gdk/gdkapplaunchcontext.h:30,
                 from /usr/include/gtk-2.0/gdk/gdk.h:32,
                 from /usr/include/gtk-2.0/gtk/gtk.h:32,
                 from foo.c:1:
/usr/include/glib-2.0/gobject/gtype.h:679:1: note: declared here
  679 | {
      | ^
In file included from /usr/include/gtk-2.0/gtk/gtktoolitem.h:31,
                 from /usr/include/gtk-2.0/gtk/gtktoolbutton.h:30,
                 from /usr/include/gtk-2.0/gtk/gtkmenutoolbutton.h:30,
                 from /usr/include/gtk-2.0/gtk/gtk.h:126,
                 from foo.c:1:
/usr/include/gtk-2.0/gtk/gtktooltips.h:73:3: error: ‘GTimeVal’ is deprecated: Use 'GDateTime' instead [-Werror=deprecated-declarations]
   73 | GTimeVal last_popdown;
      | ^~~~~~~~
In file included from /usr/include/glib-2.0/glib/galloca.h:32,
                 from /usr/include/glib-2.0/glib.h:30,
                 from /usr/include/glib-2.0/gobject/gbinding.h:28,
                 from /usr/include/glib-2.0/glib-object.h:23,
                 from /usr/include/glib-2.0/gio/gioenums.h:28,
                 from /usr/include/glib-2.0/gio/giotypes.h:28,
                 from /usr/include/glib-2.0/gio/gio.h:26,
                 from /usr/include/gtk-2.0/gdk/gdkapplaunchcontext.h:30,
                 from /usr/include/gtk-2.0/gdk/gdk.h:32,
                 from /usr/include/gtk-2.0/gtk/gtk.h:32,
                 from foo.c:1:
/usr/include/glib-2.0/glib/gtypes.h:551:8: note: declared here
  551 | struct _GTimeVal
      | ^~~~~~~~~
cc1: all warnings being treated as errors
FAIL

This is a regression since ubuntu 19.04.

Noticed while building cef.

Workaround: -DGTK_DISABLE_DEPRECATED

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: libgtk2.0-dev 2.24.32-4ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-18.19-generic 5.3.1
Uname: Linux 5.3.0-18-generic x86_64
ApportVersion: 2.20.11-0ubuntu8
Architecture: amd64
Date: Fri Oct 25 09:48:14 2019
InstallationDate: Installed on 2019-10-18 (7 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: gtk+2.0
UpgradeStatus: No upgrade log present (probably fresh install)

[Dan Kegel (dank)]

Filed https://gitlab.gnome.org/GNOME/gtk/issues/2221 in case it's an upstream bug.
I'll probably regret that.