filechooserwidget: Reimplement DnD Drop Target

This reverts commit 34752a15a71597d00a8d08befc545ac1c178b81b.

Leaving out the drag source portion as that needs a total
reimplementation.  The GtkDropTarget only required minor
modifications.

gtk/gtkfilechooserwidget.c

@@ -1585,6 +1585,115 @@ change_show_time_state (GSimpleAction *action,
   impl->show_time = g_variant_get_boolean (state);
 }
 
+/* Shows an error dialog about not being able to select a dragged file */
+static void
+error_selecting_dragged_file_dialog (GtkFileChooserWidget *impl,
+                                     GFile                 *file,
+                                     GError                *error)
+{
+  error_dialog (impl,
+                _("Could not select file"),
+                error);
+}
+
+static void
+file_list_drag_data_select_files (GtkFileChooserWidget  *impl,
+                                  GSList                *files)
+{
+  GtkFileChooser *chooser = GTK_FILE_CHOOSER (impl);
+  GSList *l;
+
+  for (l = files; l; l = l->next)
+    {
+      GFile *file = l->data;
+      GError *error = NULL;
+
+      gtk_file_chooser_widget_select_file (chooser, file, &error);
+      if (error)
+        error_selecting_dragged_file_dialog (impl, file, error);
+    }
+}
+
+typedef struct
+{
+  GtkFileChooserWidget *impl;
+  GSList *files;
+} FileListDragData;
+
+static void
+file_list_drag_data_received_get_info_cb (GObject      *source,
+                                          GAsyncResult *result,
+                                          gpointer      user_data)
+{
+  GFile *file = G_FILE (source);
+  FileListDragData *data = user_data;
+  GFileInfo *info;
+  GtkFileChooserWidget *impl = data->impl;
+  GtkFileChooser *chooser = GTK_FILE_CHOOSER (impl);
+
+  g_clear_object (&impl->file_list_drag_data_received_cancellable);
+
+  info = g_file_query_info_finish (file, result, NULL);
+  if (!info)
+    goto out;
+
+  if ((impl->action == GTK_FILE_CHOOSER_ACTION_OPEN ||
+       impl->action == GTK_FILE_CHOOSER_ACTION_SAVE) &&
+      data->files->next == NULL && _gtk_file_info_consider_as_directory (info))
+    change_folder_and_display_error (data->impl, data->files->data, FALSE);
+  else
+    {
+      GError *local_error = NULL;
+
+      gtk_file_chooser_widget_unselect_all (chooser);
+      gtk_file_chooser_widget_select_file (chooser, data->files->data, &local_error);
+      if (local_error)
+        error_selecting_dragged_file_dialog (data->impl, data->files->data, local_error);
+    }
+
+  if (impl->select_multiple)
+    file_list_drag_data_select_files (data->impl, data->files->next);
+
+out:
+  g_object_unref (data->impl);
+  g_slist_free_full (data->files, g_object_unref);
+  g_free (data);
+
+  g_clear_object (&info);
+}
+
+static gboolean
+file_list_drag_drop_cb (GtkDropTarget        *dest,
+                        const GValue         *value,
+                        double                x,
+                        double                y,
+                        GtkFileChooserWidget *impl)
+{
+  GSList *files;
+  FileListDragData *data;
+
+  files = g_value_get_boxed (value);
+
+  data = g_new0 (FileListDragData, 1);
+  data->impl = g_object_ref (impl);
+  data->files = g_slist_copy_deep (files, (GCopyFunc) g_object_ref, NULL);
+
+  if (impl->file_list_drag_data_received_cancellable)
+    g_cancellable_cancel (impl->file_list_drag_data_received_cancellable);
+  g_clear_object (&impl->file_list_drag_data_received_cancellable);
+
+  impl->file_list_drag_data_received_cancellable = g_cancellable_new ();
+  g_file_query_info_async (data->files->data,
+                           "standard::type",
+                           G_FILE_QUERY_INFO_NONE,
+                           G_PRIORITY_DEFAULT,
+                           impl->file_list_drag_data_received_cancellable,
+                           file_list_drag_data_received_get_info_cb,
+                           data);
+
+  return TRUE;
+}
+
 /* Sensitizes the "Copy file’s location" and other context menu items if there is actually
  * a selection active.
  */
@@ -7007,12 +7116,17 @@ static void
 post_process_ui (GtkFileChooserWidget *impl)
 {
   GFile            *file;
+  GtkDropTarget *target;
   GtkGesture *gesture;
   GtkEventController *controller;
   GtkShortcutTrigger *trigger;
   GtkShortcutAction *action;
   GtkShortcut *shortcut;
 
+  target = gtk_drop_target_new (GDK_TYPE_FILE_LIST, GDK_ACTION_COPY | GDK_ACTION_MOVE);
+  g_signal_connect (target, "drop", G_CALLBACK (file_list_drag_drop_cb), impl);
+  gtk_widget_add_controller (impl->browse_files_swin, GTK_EVENT_CONTROLLER (target));
+
   file = g_file_new_for_path ("/");
   _gtk_path_bar_set_file (GTK_PATH_BAR (impl->browse_path_bar), file, FALSE);
   g_object_unref (file);