[gnome-control-center/benzea/ensure-valid-config-after-loading: 5/6] display: Ensure at least one display is enabled

[Benjamin Berg <bberg src gnome org>]

commit f45dcff81f94f1ba8805fb836adbf3e5cb20087c
Author: Benjamin Berg <bberg redhat com>
Date:   Wed Mar 20 15:16:51 2019 +0100

    display: Ensure at least one display is enabled
    
    When the user has more than two monitors, then they can disable each
    monitor separately. If the user creates an invalid configuration because
    they disabled the last monitor, then enable a different one immediately.

 panels/display/cc-display-panel.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)
---
diff --git a/panels/display/cc-display-panel.c b/panels/display/cc-display-panel.c
index 13ff9ce88..c0a3438cb 100644
--- a/panels/display/cc-display-panel.c
+++ b/panels/display/cc-display-panel.c
@@ -493,8 +493,32 @@ on_output_enabled_active_changed_cb (CcDisplayPanel *panel)
   if (cc_display_monitor_is_active (panel->current_output) == active)
     return;
 
-  /* Changing the active state requires a UI rebuild. */
   cc_display_monitor_set_active (panel->current_output, active);
+
+  /* Prevent the invalid configuration of disabling the last monitor
+   * by switching on a different one. */
+  if (config_get_current_type (panel) == CC_DISPLAY_CONFIG_INVALID_NONE)
+    {
+      GList *outputs, *l;
+
+      outputs = cc_display_config_get_ui_sorted_monitors (panel->current_config);
+      for (l = outputs; l; l = l->next)
+        {
+          CcDisplayMonitor *output = CC_DISPLAY_MONITOR (l->data);
+
+          if (output == panel->current_output)
+            continue;
+
+          if (!cc_display_monitor_is_usable (output))
+            continue;
+
+          cc_display_monitor_set_active (output, TRUE);
+          cc_display_monitor_set_primary (output, TRUE);
+          break;
+        }
+    }
+
+  /* Changing the active state requires a UI rebuild. */
   rebuild_ui (panel);
 }