meldwindow: Add simple HeaderBar for the ex-application menu to live in

Ideally we'd move a bunch of our UI there, but at this point we just
want to meet the GNOME goal of removing application menu usage, and this
seems like the easiest and most future-proof option.

Author: kaiw

data/ui/application.ui

@@ -44,7 +44,7 @@ Josef Vybíral</property>
       </object>
     </child>
   </object>
-  <menu id="app-menu">
+  <menu id="gear-menu">
     <section>
       <item>
         <attribute name="label" translatable="yes">_Preferences</attribute>

data/ui/meldapp.ui

@@ -7,6 +7,29 @@
     <property name="title" translatable="yes">Meld</property>
     <property name="icon_name">org.gnome.meld</property>
     <signal name="delete-event" handler="on_delete_event" swapped="no"/>
+
+    <child type="titlebar">
+      <object class="GtkHeaderBar" id="header_bar">
+        <property name="show-close-button">true</property>
+        <property name="visible">true</property>
+        <child>
+          <object class="GtkMenuButton" id="gear_menu_button">
+            <property name="visible">true</property>
+            <property name="can_focus">False</property>
+            <child>
+              <object class="GtkImage">
+                <property name="icon-name">open-menu-symbolic</property>
+                <property name="visible">true</property>
+              </object>
+            </child>
+          </object>
+          <packing>
+            <property name="pack-type">end</property>
+          </packing>
+        </child>
+      </object>
+    </child>
+
     <child>
       <object class="GtkVBox" id="appvbox">
         <property name="visible">True</property>

meld/meldapp.py

@@ -65,11 +65,6 @@ def do_startup(self):
             action.connect('activate', callback)
             self.add_action(action)
 
-        # TODO: Should not be necessary but Builder doesn't understand Menus
-        builder = meld.ui.util.get_builder("application.ui")
-        menu = builder.get_object("app-menu")
-        self.set_app_menu(menu)
-        # self.set_menubar()
         self.new_window()
 
     def do_activate(self):

meld/meldwindow.py

@@ -251,6 +251,7 @@ def app_action(*args):
         self.ui.ensure_update()
         self.diff_handler = None
         self.undo_handlers = tuple()
+        self.widget.connect('realize', self.on_realize)
         self.widget.connect('focus_in_event', self.on_focus_change)
         self.widget.connect('focus_out_event', self.on_focus_change)
 
@@ -262,6 +263,18 @@ def app_action(*args):
         shortcut_window = builder.get_object("shortcuts-meld")
         self.widget.set_help_overlay(shortcut_window)
 
+    def on_realize(self, user_data):
+        # FIXME: Ideally this would be in do_realize, and we'd get the menu
+        # from resources, but MeldWindow would need to be a real GtkWindow
+        # subclass, and we'd need to... have resources.
+        builder = meld.ui.util.get_builder("application.ui")
+        menu = builder.get_object("gear-menu")
+        self.gear_menu_button.set_popover(
+            Gtk.Popover.new_from_model(self.gear_menu_button, menu))
+
+        app = self.widget.get_application()
+        meld.ui.util.extract_accels_from_menu(menu, app)
+
     def _on_recentmenu_map(self, recentmenu):
         for imagemenuitem in recentmenu.get_children():
             imagemenuitem.set_tooltip_text(imagemenuitem.get_label())