popup-menu: Add support for child menus

Allow opening a popup menu from another menu. While the child menu
is open, events on the parent menu are blocked. The parent menu
is kept open when the child menu is closed; the child menu on the
other hand is closed with the parent, e.g. when the focus moves
to another toplevel menu.
This feature will be used to implement combo box menu items.

https://bugzilla.gnome.org/show_bug.cgi?id=652837

js/ui/popupMenu.js

@@ -800,6 +800,7 @@ PopupMenuBase.prototype = {
         this.passEvents = false;
 
         this._activeMenuItem = null;
+        this._childMenus = [];
     },
 
     addAction: function(title, callback) {
@@ -831,6 +832,28 @@ PopupMenuBase.prototype = {
         return menuItem;
     },
 
+    isChildMenu: function(menu) {
+        return this._childMenus.indexOf(menu) != -1;
+    },
+
+    addChildMenu: function(menu) {
+        if (this.isChildMenu(menu))
+            return;
+
+        this._childMenus.push(menu);
+        this.emit('child-menu-added', menu);
+    },
+
+    removeChildMenu: function(menu) {
+        let index = this._childMenus.indexOf(menu);
+
+        if (index == -1)
+            return;
+
+        this._childMenus.splice(index, 1);
+        this.emit('child-menu-removed', menu);
+    },
+
     /**
      * _connectSubMenuSignals:
      * @object: a menu item, or a menu section
@@ -1400,6 +1423,7 @@ PopupMenuManager.prototype = {
         this._keyFocusNotifyId = 0;
         this._activeMenu = null;
         this._menus = [];
+        this._menuStack = [];
         this._preGrabInputMode = null;
         this._grabbedFromKeynav = false;
     },
@@ -1408,6 +1432,8 @@ PopupMenuManager.prototype = {
         let menudata = {
             menu:              menu,
             openStateChangeId: menu.connect('open-state-changed', Lang.bind(this, this._onMenuOpenState)),
+            childMenuAddedId:  menu.connect('child-menu-added', Lang.bind(this, this._onChildMenuAdded)),
+            childMenuRemovedId: menu.connect('child-menu-removed', Lang.bind(this, this._onChildMenuRemoved)),
             destroyId:         menu.connect('destroy', Lang.bind(this, this._onMenuDestroy)),
             enterId:           0,
             focusInId:         0
@@ -1435,6 +1461,8 @@ PopupMenuManager.prototype = {
 
         let menudata = this._menus[position];
         menu.disconnect(menudata.openStateChangeId);
+        menu.disconnect(menudata.childMenuAddedId);
+        menu.disconnect(menudata.childMenuRemovedId);
         menu.disconnect(menudata.destroyId);
 
         if (menudata.enterId)
@@ -1472,8 +1500,20 @@ PopupMenuManager.prototype = {
     },
 
     _onMenuOpenState: function(menu, open) {
-        if (open)
+        if (open) {
+            if (this._activeMenu && this._activeMenu.isChildMenu(menu)) {
+                this._menuStack.push(this._activeMenu);
+                menu.actor.grab_key_focus();
+            }
             this._activeMenu = menu;
+        } else {
+            if (this._menuStack.length > 0) {
+                this._activeMenu = this._menuStack.pop();
+                if (menu.sourceActor)
+                    menu.sourceActor.grab_key_focus();
+                this._didPop = true;
+            }
+        }
 
         // Check what the focus was before calling pushModal/popModal
         let focus = global.stage.key_focus;
@@ -1506,6 +1546,14 @@ PopupMenuManager.prototype = {
         }
     },
 
+    _onChildMenuAdded: function(menu, childMenu) {
+        this.addMenu(childMenu);
+    },
+
+    _onChildMenuRemoved: function(menu, childMenu) {
+        this.removeMenu(childMenu);
+    },
+
     // change the currently-open menu without dropping grab
     _changeMenu: function(newMenu) {
         if (this._activeMenu) {
@@ -1514,6 +1562,8 @@ PopupMenuManager.prototype = {
             // before closing it to keep that from happening
             let oldMenu = this._activeMenu;
             this._activeMenu = null;
+            for (let i = this._menuStack.length - 1; i >= 0; i--)
+                this._menuStack[i].close(false);
             oldMenu.close(false);
             newMenu.open(false);
         } else
@@ -1524,6 +1574,15 @@ PopupMenuManager.prototype = {
         if (!this.grabbed || menu == this._activeMenu)
             return false;
 
+        if (this._activeMenu && this._activeMenu.isChildMenu(menu))
+            return false;
+
+        if (this._menuStack.indexOf(menu) != -1)
+            return false;
+
+        if (this._menuStack.length > 0 && this._menuStack[0].isChildMenu(menu))
+            return false;
+
         this._changeMenu(menu);
         return false;
     },
@@ -1536,6 +1595,8 @@ PopupMenuManager.prototype = {
         if (focus) {
             if (this._activeMenuContains(focus))
                 return;
+            if (this._menuStack.length > 0)
+                return;
             if (focus._delegate && focus._delegate.menu &&
                 this._findMenu(focus._delegate.menu) != -1)
                 return;
@@ -1594,6 +1655,11 @@ PopupMenuManager.prototype = {
         if (this._activeMenu != null && this._activeMenu.passEvents)
             return false;
 
+        if (this._didPop) {
+            this._didPop = false;
+            return true;
+        }
+
         let activeMenuContains = this._eventIsOnActiveMenu(event);
         let eventType = event.type();