This patch makes GTK+ look for additional modules in a list of directories
specified by the environment variable "GUIX_GTK3_PATH".  This can be used
instead of "GTK_PATH" to make GTK+ find modules that are incompatible with
other major versions of GTK+.

--- a/gtk/gtkmodules.c	2015-09-20 20:09:05.060590217 +0200
+++ b/gtk/gtkmodules.c	2015-09-20 20:10:33.423124833 +0200
@@ -52,6 +52,7 @@
 get_module_path (void)
 {
   const gchar *module_path_env;
+  const gchar *module_guix_gtk3_path_env;
   const gchar *exe_prefix;
   gchar *module_path;
   gchar *default_dir;
@@ -61,6 +62,7 @@
     return result;
 
   module_path_env = g_getenv ("GTK_PATH");
+  module_guix_gtk3_path_env = g_getenv ("GUIX_GTK3_PATH");
   exe_prefix = g_getenv ("GTK_EXE_PREFIX");
 
   if (exe_prefix)
@@ -68,7 +70,13 @@
   else
     default_dir = g_build_filename (_gtk_get_libdir (), "gtk-3.0", NULL);
 
-  if (module_path_env)
+  if (module_guix_gtk3_path_env && module_path_env)
+    module_path = g_build_path (G_SEARCHPATH_SEPARATOR_S,
+				module_guix_gtk3_path_env, module_path_env, default_dir, NULL);
+  else if (module_guix_gtk3_path_env)
+    module_path = g_build_path (G_SEARCHPATH_SEPARATOR_S,
+				module_guix_gtk3_path_env, default_dir, NULL);
+  else if (module_path_env)
     module_path = g_build_path (G_SEARCHPATH_SEPARATOR_S,
 				module_path_env, default_dir, NULL);
   else
a086fd18b2fa145177'>commit</a><a href='/guix/diff/gnu/services/base.scm?id=45cdf3ad61c28272abf71fa086fd18b2fa145177'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/base.scm'>
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<div class='path'>path: <a href='/guix/log/?id=45cdf3ad61c28272abf71fa086fd18b2fa145177'>root</a>/<a href='/guix/log/gnu?id=45cdf3ad61c28272abf71fa086fd18b2fa145177'>gnu</a>/<a href='/guix/log/gnu/services?id=45cdf3ad61c28272abf71fa086fd18b2fa145177'>services</a>/<a href='/guix/log/gnu/services/base.scm?id=45cdf3ad61c28272abf71fa086fd18b2fa145177'>base.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/services/base.scm?id=45cdf3ad61c28272abf71fa086fd18b2fa145177&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-04-03 22:08:33 +0200'>2021-04-03</span></td><td><a href='/guix/commit/gnu/services/base.scm?id=58beda01217c48da52e67ac5461f33b6532b5ede'>services: guix-publish: Add zstd compression by default.</a><span class='msg-avail'>...<span class='msg-tooltip'>That way, the default config with (advertises? #t) and without a cache
will offer zstd-compressed substitutes, which should lead to much higher
throughput than gzip.

* gnu/services/base.scm (default-compression): When
'guix-publish-configuration-cache' returns true, use higher level
compression ratios.  Add "zstd".
* doc/guix.texi (Base Services): Mention zstd.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-04-01 13:40:09 +0200'>2021-04-01</span></td><td><a href='/guix/commit/gnu/services/base.scm?id=aa03d32eb1d2c41ee6251b3df59eb5177bdf5d82'>services: kmscon: Add font-engine and font-size fields.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/base.scm (&lt;kmscon-configuration&gt;): Add font-engine and
font-size fields.
(kmscon-service-type): Honor them.
* doc/guix.texi (Base Services): Document them.
</span></span></td><td>qblade</td></tr>