test-runner: Add ability to perform actions on signals callbacks

An action can be performed both on a signal emitted by a window or by
a well-known signal name, so that one can do:

  [window-id]::signal => command

 And so these would work:
  w/1::position-changed => resize w/2 20 30
  ::monitors-changed => move w/1 30 40

We only support "monitors-changed" global signal name or connecting to
window signals for now, but this can be easily expanded adding support
for more global signal values or parsing other kinds of object instances

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3701>

src/tests/test-runner.c

@@ -53,6 +53,13 @@ typedef struct {
 
 #define META_SIDE_TEST_CASE_NONE G_MAXINT32
 
+static gboolean test_case_do (TestCase    *test,
+                              const char  *filename,
+                              int          line_no,
+                              int          argc,
+                              char       **argv,
+                              GError     **error);
+
 static void
 set_true_cb (gboolean *value)
 {
@@ -728,6 +735,113 @@ test_case_clear_struts (TestCase  *test,
   return TRUE;
 }
 
+typedef struct
+{
+  TestCase *test_case;
+  const char *filename;
+  int line_no;
+  int argc;
+  char **argv;
+  GError **error;
+  GObject *instance;
+  gulong handler_id;
+} TestCaseArgs;
+
+static void
+test_case_signal_cb (TestCaseArgs *test_case_args)
+{
+  g_autoptr (GError) error = NULL;
+
+  g_signal_handler_disconnect (test_case_args->instance,
+                               test_case_args->handler_id);
+
+  if (!test_case_do (test_case_args->test_case,
+                     test_case_args->filename,
+                     test_case_args->line_no,
+                     test_case_args->argc,
+                     test_case_args->argv,
+                     &error))
+    g_warning ("Failed to run test command in signal handler: %s",
+               error->message);
+
+  g_strfreev (test_case_args->argv);
+  g_free (test_case_args);
+}
+
+static gboolean
+test_case_parse_signal (TestCase *test,
+                        int       argc,
+                        char    **argv,
+                        char    **out_signal_name,
+                        GObject **out_signal_instance,
+                        GError  **error)
+{
+  const char *signal_start;
+  GObject *instance_obj = NULL;
+  const char *signal_name;
+
+  *out_signal_instance = NULL;
+  *out_signal_name = NULL;
+
+  if (argc < 3 || !g_str_equal (argv[1], "=>"))
+    BAD_COMMAND ("usage: [window-id]::signal => command");
+
+  signal_start = strstr (argv[0], "::");
+  if (!signal_start)
+    BAD_COMMAND ("Invalid syntax, no signal parameter");
+
+  signal_name = signal_start + 2;
+
+  if (!strlen (signal_name))
+    BAD_COMMAND ("Invalid syntax, empty signal name");
+
+  if (signal_start != argv[0])
+    {
+      g_autofree char *instance = g_strndup (argv[0], signal_start - argv[0]);
+      MetaTestClient *client;
+      const char *window_id;
+      MetaWindow *window;
+
+      if (!test_case_parse_window_id (test, instance, &client,
+                                      &window_id, error))
+        BAD_COMMAND ("Cannot find window for instance %s", instance);
+
+      window = meta_test_client_find_window (client, window_id, error);
+      if (!window)
+        BAD_COMMAND ("Cannot find window for window id %s", window_id);
+
+      instance_obj = G_OBJECT (window);
+    }
+
+  if (!instance_obj)
+    {
+      if (g_str_equal (signal_name, "monitors-changed"))
+        {
+          MetaBackend *backend = meta_context_get_backend (test->context);
+          MetaMonitorManager *monitor_manager =
+            meta_backend_get_monitor_manager (backend);
+
+          instance_obj = G_OBJECT (monitor_manager);
+        }
+      else
+        {
+          BAD_COMMAND ("Unknown global signal name '%s'", signal_name);
+        }
+    }
+
+  if (!g_signal_lookup (signal_name, G_TYPE_FROM_INSTANCE (instance_obj)))
+    {
+      BAD_COMMAND ("No signal '%s' in object of type %s",
+                   signal_name,
+                   g_type_name_from_instance ((GTypeInstance *) instance_obj));
+    }
+
+  *out_signal_instance = g_object_ref (instance_obj);
+  *out_signal_name = g_strdup (signal_name);
+
+  return TRUE;
+}
+
 static gboolean
 test_case_do (TestCase    *test,
               const char  *filename,
@@ -1794,6 +1908,33 @@ test_case_do (TestCase    *test,
                                         (gpointer *) &window_actor);
         }
     }
+  else if (argc > 2 && g_str_equal (argv[1], "=>"))
+    {
+      g_autoptr (GObject) signal_instance = NULL;
+      g_autofree char *signal_name = NULL;
+      TestCaseArgs *test_case_args;
+
+      if (!test_case_parse_signal (test, argc, argv,
+                                   &signal_name, &signal_instance, error))
+        return FALSE;
+
+      g_debug ("Connected to signal '%s' on object %p (%s)",
+               signal_name, signal_instance,
+               g_type_name_from_instance ((GTypeInstance *) signal_instance));
+
+      test_case_args = g_new0 (TestCaseArgs, 1);
+      test_case_args->test_case = test;
+      test_case_args->filename = filename;
+      test_case_args->line_no = line_no;
+      test_case_args->argc = argc - 2;
+      test_case_args->argv = g_strdupv (&argv[2]);
+      test_case_args->instance = signal_instance;
+      test_case_args->handler_id =
+        g_signal_connect_swapped (signal_instance,
+                                  signal_name,
+                                  G_CALLBACK (test_case_signal_cb),
+                                  test_case_args);
+    }
   else
     {
       BAD_COMMAND("Unknown command %s", argv[0]);