views/month-cell: Add activate signal

This will be needed for keyboard navigation.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/564>

src/gui/views/gcal-month-cell.blp

@@ -9,6 +9,7 @@ template $GcalMonthCell: Widget {
   }
 
   accessible-role: grid_cell;
+  receives-default: true;
   focusable: true;
 
   Adw.BreakpointBin breakpoint_bin {

src/gui/views/gcal-month-cell.c

@@ -62,6 +62,7 @@ G_DEFINE_TYPE (GcalMonthCell, gcal_month_cell, GTK_TYPE_WIDGET)
 enum
 {
   SHOW_OVERFLOW,
+  ACTIVATE,
   N_SIGNALS
 };
 
@@ -441,6 +442,40 @@ gcal_month_cell_class_init (GcalMonthCellClass *klass)
                                          1,
                                          GTK_TYPE_WIDGET);
 
+  signals[ACTIVATE] = g_signal_new ("activate",
+                                    GCAL_TYPE_MONTH_CELL,
+                                    G_SIGNAL_RUN_FIRST | G_SIGNAL_ACTION,
+                                    0,
+                                    NULL, NULL,
+                                    g_cclosure_marshal_VOID__VOID,
+                                    G_TYPE_NONE,
+                                    0);
+
+  gtk_widget_class_set_activate_signal (widget_class, signals[ACTIVATE]);
+
+  {
+    g_autoptr (GtkShortcutAction) activate_action = NULL;
+    const guint activate_keyvals[] = {
+      GDK_KEY_space,
+      GDK_KEY_KP_Space,
+      GDK_KEY_Return,
+      GDK_KEY_ISO_Enter,
+      GDK_KEY_KP_Enter,
+    };
+
+    activate_action = gtk_signal_action_new ("activate");
+
+    for (size_t i = 0; i < G_N_ELEMENTS (activate_keyvals); i++)
+      {
+        g_autoptr (GtkShortcut) activate_shortcut = NULL;
+
+        activate_shortcut = gtk_shortcut_new (gtk_keyval_trigger_new (activate_keyvals[i], 0),
+                                              g_object_ref (activate_action));
+
+        gtk_widget_class_add_shortcut (widget_class, activate_shortcut);
+      }
+  }
+
   properties[PROP_CONTEXT] = g_param_spec_object ("context",
                                                   "Context",
                                                   "The GcalContext of the application",