Don't let themes override explicit border-width in dialogs

This fixes an issue where the theme-provided border-width prevents
dialog contents from lining up properly with the headerbar. To make
this work in message dialogs, we have to explicitly set the border-
width of the action area to 0.

gtk/gtkcontainer.c

@@ -247,6 +247,7 @@ struct _GtkContainerPrivate
   guint resize_handler;
 
   guint border_width : 16;
+  guint border_width_set   : 1;
 
   guint has_focus_chain    : 1;
   guint reallocate_redraws : 1;
@@ -1381,6 +1382,7 @@ gtk_container_init (GtkContainer *container)
   priv->border_width = 0;
   priv->resize_mode = GTK_RESIZE_PARENT;
   priv->reallocate_redraws = FALSE;
+  priv->border_width_set = FALSE;
 }
 
 static void
@@ -1462,6 +1464,31 @@ gtk_container_get_property (GObject         *object,
     }
 }
 
+gboolean
+_gtk_container_get_border_width_set (GtkContainer *container)
+{
+  GtkContainerPrivate *priv;
+
+  g_return_val_if_fail (GTK_IS_CONTAINER (container), FALSE);
+
+  priv = container->priv;
+
+  return priv->border_width_set;
+}
+
+void
+_gtk_container_set_border_width_set (GtkContainer *container,
+                                     gboolean      border_width_set)
+{
+  GtkContainerPrivate *priv;
+
+  g_return_if_fail (GTK_IS_CONTAINER (container));
+
+  priv = container->priv;
+
+  priv->border_width_set = border_width_set ? TRUE : FALSE;
+}
+
 /**
  * gtk_container_set_border_width:
  * @container: a #GtkContainer
@@ -1492,6 +1519,8 @@ gtk_container_set_border_width (GtkContainer *container,
   if (priv->border_width != border_width)
     {
       priv->border_width = border_width;
+      _gtk_container_set_border_width_set (container, TRUE);
+
       g_object_notify (G_OBJECT (container), "border-width");
 
       if (gtk_widget_get_realized (GTK_WIDGET (container)))

gtk/gtkcontainerprivate.h

@@ -41,6 +41,9 @@ gboolean _gtk_container_get_reallocate_redraws (GtkContainer *container);
 
 void      _gtk_container_stop_idle_sizer        (GtkContainer *container);
 void      _gtk_container_maybe_start_idle_sizer (GtkContainer *container);
+gboolean  _gtk_container_get_border_width_set   (GtkContainer *container);
+void      _gtk_container_set_border_width_set   (GtkContainer *container,
+                                                 gboolean      border_width_set);
 
 G_END_DECLS
 

gtk/gtkdialog.c

@@ -35,6 +35,7 @@
 #include "gtkmarshalers.h"
 #include "gtkbox.h"
 #include "gtkboxprivate.h"
+#include "gtkcontainerprivate.h"
 #include "gtkmain.h"
 #include "gtkintl.h"
 #include "gtkbindings.h"
@@ -566,6 +567,15 @@ gtk_dialog_class_init (GtkDialogClass *class)
 		  _gtk_marshal_VOID__VOID,
 		  G_TYPE_NONE, 0);
 
+  /**
+   * GtkDialog:content-area-border:
+   *
+   * The default border width used around the
+   * content area of the dialog, as returned by
+   * gtk_dialog_get_content_area(), unless gtk_container_set_border_width()
+   * was called on that widget directly.
+   *
+   */
   gtk_widget_class_install_style_property (widget_class,
 					   g_param_spec_int ("content-area-border",
                                                              P_("Content area border"),
@@ -656,9 +666,11 @@ update_spacings (GtkDialog *dialog)
                         "button-spacing", &button_spacing,
                         "action-area-border", &action_area_border,
                         NULL);
-  
-  gtk_container_set_border_width (GTK_CONTAINER (priv->vbox),
-                                  content_area_border);
+
+  if (!_gtk_container_get_border_width_set (GTK_CONTAINER (priv->vbox)))
+    gtk_container_set_border_width (GTK_CONTAINER (priv->vbox),
+                                    content_area_border);
+
   if (!_gtk_box_get_spacing_set (GTK_BOX (priv->vbox)))
     {
       gtk_box_set_spacing (GTK_BOX (priv->vbox), content_area_spacing);
@@ -667,8 +679,10 @@ update_spacings (GtkDialog *dialog)
 
   gtk_box_set_spacing (GTK_BOX (priv->action_area),
                        button_spacing);
-  gtk_container_set_border_width (GTK_CONTAINER (priv->action_area),
-                                  action_area_border);
+
+  if (!_gtk_container_get_border_width_set (GTK_CONTAINER (priv->action_area)))
+    gtk_container_set_border_width (GTK_CONTAINER (priv->action_area),
+                                    action_area_border);
 }
 
 static void

gtk/resources/ui/gtkmessagedialog.ui

@@ -87,6 +87,11 @@
             <property name="position">0</property>
           </packing>
         </child>
+        <child internal-child="action_area">
+          <object class="GtkButtonBox">
+            <property name="border_width">0</property>
+          </object>
+        </child>
       </object>
     </child>
   </template>