prefs: Add dynamic-workspaces setting

We currently sync the number of workspaces with the corresponding
preference. This is not really useful with GNOME Shell's dynamic
handling of workspaces, not least as the setting is effectively
ignored. Worse, it will trigger writes to dconf on login, slowing
down startup, so add a setting to indicate that workspaces are managed
dynamically and really ignore the num-workspaces setting when set.

https://bugzilla.gnome.org/show_bug.cgi?id=671568

src/core/prefs.c

@@ -82,6 +82,7 @@ static int num_workspaces = 4;
 static GDesktopTitlebarAction action_double_click_titlebar = G_DESKTOP_TITLEBAR_ACTION_TOGGLE_MAXIMIZE;
 static GDesktopTitlebarAction action_middle_click_titlebar = G_DESKTOP_TITLEBAR_ACTION_LOWER;
 static GDesktopTitlebarAction action_right_click_titlebar = G_DESKTOP_TITLEBAR_ACTION_MENU;
+static gboolean dynamic_workspaces = FALSE;
 static gboolean application_based = FALSE;
 static gboolean disable_workarounds = FALSE;
 static gboolean auto_raise = FALSE;
@@ -280,6 +281,13 @@ static MetaBoolPreference preferences_bool[] =
       },
       &use_system_font,
     },
+    {
+      { "dynamic-workspaces",
+        SCHEMA_MUTTER,
+        META_PREF_DYNAMIC_WORKSPACES,
+      },
+      &dynamic_workspaces,
+    },
     {
       { "application-based",
         SCHEMA_GENERAL,
@@ -1498,6 +1506,12 @@ meta_prefs_get_num_workspaces (void)
   return num_workspaces;
 }
 
+gboolean
+meta_prefs_get_dynamic_workspaces (void)
+{
+  return dynamic_workspaces;
+}
+
 gboolean
 meta_prefs_get_application_based (void)
 {

src/core/screen.c

@@ -1173,7 +1173,9 @@ prefs_changed_callback (MetaPreference pref,
 {
   MetaScreen *screen = data;
   
-  if (pref == META_PREF_NUM_WORKSPACES)
+  if ((pref == META_PREF_NUM_WORKSPACES ||
+       pref == META_PREF_DYNAMIC_WORKSPACES) &&
+      !meta_prefs_get_dynamic_workspaces ())
     {
       /* GSettings doesn't provide timestamps, but luckily update_num_workspaces
        * often doesn't need it...
@@ -1483,7 +1485,9 @@ meta_screen_remove_workspace (MetaScreen *screen, MetaWorkspace *workspace,
   new_num = g_list_length (screen->workspaces);
 
   set_number_of_spaces_hint (screen, new_num);
-  meta_prefs_set_num_workspaces (new_num);
+
+  if (!meta_prefs_get_dynamic_workspaces ())
+    meta_prefs_set_num_workspaces (new_num);
 
   /* If deleting a workspace before the current workspace, the active
    * workspace index changes, so we need to update that hint */
@@ -1538,7 +1542,9 @@ meta_screen_append_new_workspace (MetaScreen *screen, gboolean activate,
   new_num = g_list_length (screen->workspaces);
 
   set_number_of_spaces_hint (screen, new_num);
-  meta_prefs_set_num_workspaces (new_num);
+
+  if (!meta_prefs_get_dynamic_workspaces ())
+    meta_prefs_set_num_workspaces (new_num);
 
   meta_screen_queue_workarea_recalc (screen);
 

src/meta/prefs.h

@@ -47,6 +47,7 @@ typedef enum
   META_PREF_THEME,
   META_PREF_TITLEBAR_FONT,
   META_PREF_NUM_WORKSPACES,
+  META_PREF_DYNAMIC_WORKSPACES,
   META_PREF_APPLICATION_BASED,
   META_PREF_KEYBINDINGS,
   META_PREF_DISABLE_WORKAROUNDS,
@@ -94,6 +95,7 @@ const char*                 meta_prefs_get_theme              (void);
 /* returns NULL if GTK default should be used */
 const PangoFontDescription* meta_prefs_get_titlebar_font      (void);
 int                         meta_prefs_get_num_workspaces     (void);
+gboolean                    meta_prefs_get_dynamic_workspaces (void);
 gboolean                    meta_prefs_get_application_based  (void);
 gboolean                    meta_prefs_get_disable_workarounds (void);
 gboolean                    meta_prefs_get_auto_raise         (void);

src/org.gnome.mutter.gschema.xml.in

@@ -45,6 +45,16 @@
       </_description>
     </key>
 
+    <key name="dynamic-workspaces" type="b">
+      <default>false</default>
+      <_summary>Workspaces are managed dynamically</_summary>
+      <_description>
+        Determines whether workspaces are managed dynamically or
+        whether there's a static number of workspaces (determined
+        by the num-workspaces key in org.gnome.desktop.wm.preferences).
+      </_description>
+    </key>
+
     <key name="workspaces-only-on-primary" type="b">
       <default>false</default>
       <_summary>Workspaces only on primary</_summary>