GMarkup: add G_MARKUP_IGNORE_QUALIFIED

Add a flag to GMarkupParserFlags to ignore qualified tags (along with
their contents) and attributes.

This will provide a nice way for some of our parsers (GDBus
introspection, GSettings schema, etc) to ignore additional tags that
users have added to their files, under a different namespace.

https://bugzilla.gnome.org/show_bug.cgi?id=665634

glib/gmarkup.c

@@ -1004,21 +1004,39 @@ static inline void
 emit_start_element (GMarkupParseContext  *context,
                     GError              **error)
 {
-  int i;
+  int i, j = 0;
   const gchar *start_name;
   const gchar **attr_names;
   const gchar **attr_values;
   GError *tmp_error;
 
+  /* In case we want to ignore qualified tags and we see that we have
+   * one here, we push a subparser.  This will ignore all tags inside of
+   * the qualified tag.
+   *
+   * We deal with the end of the subparser from emit_end_element.
+   */
+  if (context->flags & G_MARKUP_IGNORE_QUALIFIED && strchr (current_element (context), ':'))
+    {
+      static const GMarkupParser ignore_parser;
+      g_markup_parse_context_push (context, &ignore_parser, NULL);
+      return;
+    }
+
   attr_names = g_newa (const gchar *, context->cur_attr + 2);
   attr_values = g_newa (const gchar *, context->cur_attr + 2);
   for (i = 0; i < context->cur_attr + 1; i++)
     {
-      attr_names[i] = context->attr_names[i]->str;
+      /* Possibly omit qualified attribute names from the list */
-      attr_values[i] = context->attr_values[i]->str;
+      if ((context->flags & G_MARKUP_IGNORE_QUALIFIED) && strchr (context->attr_names[i]->str, ':'))
+        continue;
+
+      attr_names[j] = context->attr_names[i]->str;
+      attr_values[j] = context->attr_values[i]->str;
+      j++;
     }
-  attr_names[i] = NULL;
+  attr_names[j] = NULL;
-  attr_values[i] = NULL;
+  attr_values[j] = NULL;
 
   /* Call user callback for element start */
   tmp_error = NULL;
@@ -1051,6 +1069,14 @@ emit_end_element (GMarkupParseContext  *context,
 
   possibly_finish_subparser (context);
 
+  /* We might have just returned from our ignore subparser */
+  if (context->flags & G_MARKUP_IGNORE_QUALIFIED && strchr (current_element (context), ':'))
+    {
+      g_markup_parse_context_pop (context);
+      pop_tag (context);
+      return;
+    }
+
   tmp_error = NULL;
   if (context->parser->end_element)
     (* context->parser->end_element) (context,

glib/gmarkup.h

@@ -87,6 +87,10 @@ GQuark g_markup_error_quark (void);
  *     caller know the location of the error. When this flag is set the
  *     location information is also prefixed to errors generated by the
  *     #GMarkupParser implementation functions
+ * @G_MARKUP_IGNORE_QUALIFIED: Ignore (don't report) qualified
+ *     attributes and tags, along with their contents.  A qualified
+ *     attribute or tag is one that contains ':' in its name (ie: is in
+ *     another namespace).  Since: 2.40.
  *
  * Flags that affect the behaviour of the parser.
  */
@@ -94,7 +98,8 @@ typedef enum
 {
   G_MARKUP_DO_NOT_USE_THIS_UNSUPPORTED_FLAG = 1 << 0,
   G_MARKUP_TREAT_CDATA_AS_TEXT              = 1 << 1,
-  G_MARKUP_PREFIX_ERROR_POSITION            = 1 << 2
+  G_MARKUP_PREFIX_ERROR_POSITION            = 1 << 2,
+  G_MARKUP_IGNORE_QUALIFIED                 = 1 << 3
 } GMarkupParseFlags;
 
 /**