barrier: Add GInitable based constructor method

This one does proper error reporting. Via Javascript, barriers are
constructed directly via GObject construction, which currently can't
handle error reporting, but when calling from C we can. However, if we
initialize using GInitable, and use that in our constructor method, once
gjs gains support for construction using GInitable, including the error
reporting, we'll automatically get proper error reporting to Javascript.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2442>

src/backends/meta-barrier.c

@@ -35,7 +35,13 @@ typedef struct _MetaBarrierPrivate
   MetaBarrierImpl *impl;
 } MetaBarrierPrivate;
 
-G_DEFINE_TYPE_WITH_PRIVATE (MetaBarrier, meta_barrier, G_TYPE_OBJECT)
+static void initable_iface_init (GInitableIface *initable_iface);
+
+G_DEFINE_TYPE_WITH_CODE (MetaBarrier, meta_barrier, G_TYPE_OBJECT,
+                         G_ADD_PRIVATE (MetaBarrier)
+                         G_IMPLEMENT_INTERFACE (G_TYPE_INITABLE,
+                                                initable_iface_init))
+
 G_DEFINE_TYPE (MetaBarrierImpl, meta_barrier_impl, G_TYPE_OBJECT)
 
 G_STATIC_ASSERT ((int) META_BARRIER_DIRECTION_POSITIVE_X ==
@@ -225,6 +231,31 @@ meta_barrier_release (MetaBarrier      *barrier,
     META_BARRIER_IMPL_GET_CLASS (impl)->release (impl, event);
 }
 
+static gboolean
+meta_barrier_initable_init (GInitable     *initable,
+                            GCancellable  *cancellable,
+                            GError       **error)
+{
+  MetaBarrier *barrier = META_BARRIER (initable);
+  MetaBarrierPrivate *priv = meta_barrier_get_instance_private (barrier);
+
+  priv = meta_barrier_get_instance_private (barrier);
+  if (!priv->impl)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Failed to create barrier impl");
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
+static void
+initable_iface_init (GInitableIface *initable_iface)
+{
+  initable_iface->init = meta_barrier_initable_init;
+}
+
 static void
 init_barrier_impl (MetaBarrier *barrier)
 {
@@ -393,6 +424,26 @@ meta_barrier_init (MetaBarrier *barrier)
 {
 }
 
+MetaBarrier *
+meta_barrier_new (MetaBackend           *backend,
+                  int                    x1,
+                  int                    y1,
+                  int                    x2,
+                  int                    y2,
+                  MetaBarrierDirection   directions,
+                  GError               **error)
+{
+  return g_initable_new (META_TYPE_BARRIER,
+                         NULL, error,
+                         "backend", backend,
+                         "x1", x1,
+                         "y1", y1,
+                         "x2", x2,
+                         "y2", y2,
+                         "directions", directions,
+                         NULL);
+}
+
 void
 meta_barrier_emit_hit_signal (MetaBarrier      *barrier,
                               MetaBarrierEvent *event)

src/meta/barrier.h

@@ -33,6 +33,15 @@ G_DECLARE_FINAL_TYPE (MetaBarrier, meta_barrier,
 
 typedef struct _MetaBarrierEvent MetaBarrierEvent;
 
+META_EXPORT
+MetaBarrier * meta_barrier_new (MetaBackend           *backend,
+                                int                    x1,
+                                int                    y1,
+                                int                    x2,
+                                int                    y2,
+                                MetaBarrierDirection   directions,
+                                GError               **error);
+
 META_EXPORT
 gboolean meta_barrier_is_active (MetaBarrier *barrier);