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
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<div class='path'>path: <a href='/guix/log/?id=6a0d0c3c473d51d113d0c4efd7ed85d542f45c09'>root</a>/<a href='/guix/log/build-aux?id=6a0d0c3c473d51d113d0c4efd7ed85d542f45c09'>build-aux</a>/<a href='/guix/log/build-aux/test-driver.scm?id=6a0d0c3c473d51d113d0c4efd7ed85d542f45c09'>test-driver.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/build-aux/test-driver.scm?id=6a0d0c3c473d51d113d0c4efd7ed85d542f45c09&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-02-02 00:28:49 -0500'>2021-02-02</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=5e652e94a9203e0cfa27e93a89878439b7900001'>build: Add a --show-duration option to the SCM test-driver.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/test-driver.scm (script-version): Update.
(show-help): Document it.
(%options): Add the 'show-duration' option.
(test-runner-gnu): Pass as a new argument.
[test-cases-start-time]: New inner variable.
[test-on-test-begin-gnu]: New hook, used to record the start time.
[test-on-test-end-gnu]: Conditionally print elapsed time.  Record it as the
optional metadata in the test result file (.trs).
* doc/guix.texi (Running the Test Suite): Document it.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:28:46 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=26a66d0feaab7626c4053071d5557394931fe14b'>build: test-driver.scm: Allow running as a standalone script.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/test-driver.scm: Add an exec-based shebang and set the script
executable bit.
(main): Insert a newline after the version string is printed with --version.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:28:46 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=93a628c4e4f4a7f6665190f3c52a417daebaf28a'>build: test-driver.scm: Add a new '--errors-only' option.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/test-driver.scm (show-help): Add the help text for the
new '--errors-only' option.
(%options): Add the errors-only option.
(test-runner-gnu): Add the errors-only? parameter and update doc.  Move the
logging of the test data after the test has completed, so a choice can be made
whether to keep it or discard it based on the value of the test result.
(main): Pass the errors-only? option to the driver.
* doc/guix.texi (Running the Test Suite): Document the new option.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:28:37 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=a1ea2acb376c8a74f41ce0e683680417207b365a'>build: test-driver.scm: Add test cases filtering options.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/test-driver.scm (show-help): Add help text for the new --select
and --exclude options.
(%options): Add the new select and exclude options.
(test-runner-gnu): Pass them to the test runner.  Update doc.
(test-match-name*, test-match-name*/negated, %test-match-all): New variables.
(main): Compute the test specifier based on the values of the new options and
apply it to the current test runner when running the test file.
* doc/guix.texi (Running the Test Suite): Document the new options.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:23:41 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=346210b1b2130112dd5f894c1d40afb37c1c51a5'>build: test-driver.scm: Enable colored test results by default.</a><span class='msg-avail'>...<span class='msg-tooltip'>The Automake parallel test harness does its own smart detection of the
terminal color capability and always provides the --color-tests argument to
the driver.  This change defaults the --color-tests argument to true when the
test driver is run on its own (not via Automake).

* build-aux/test-driver.scm (main): Set the default value of the --color-tests
argument to true when it's not explicitly provided.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:23:41 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=13f299b2c98cce0ede3a8a37dd11832fdb3827bb'>build: test-driver.scm: Make output redirection optional.</a><span class='msg-avail'>...<span class='msg-tooltip'>This makes it easier (and less surprising) for users to experiment with the
custom Scheme test driver directly.  The behavior is unchanged from Automake's
point of view.

* build-aux/test-driver.scm (main): Make the --log-file and --trs-file
arguments optional and update doc.  Only open, redirect and close a port to a log file when
the --log-file option is provided.  Only open and close a port to a trs file
when the --trs-file option is provided.
(test-runner-gnu): Set OUT-PORT parameter default value to the current output
port.  Set the TRS-PORT parameter default value to a void port.  Update doc.
</span></span></td><td>Maxim Cournoyer</td></tr>