[gtksourceview] ContextEngine: set a GtkTextTag name for context classes

[Sébastien Wilmet <swilmet src gnome org>]

commit a3e289b2cde7f6cfb62cc9c24f64d8d2a8df39ad
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Fri May 8 11:57:17 2015 +0200

    ContextEngine: set a GtkTextTag name for context classes
    
    The use case is for GtkSpell to use the no-spell-check context class
    without a hard-dependency on GtkSourceView (GtkSpell only depends on
    GTK+).
    
    There should be no visible performance difference. The tag is just
    inserted in a hash table in the tag table.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=749100

 gtksourceview/gtksourcebuffer.c        |   11 +++++++++++
 gtksourceview/gtksourcecontextengine.c |    8 +++++++-
 2 files changed, 18 insertions(+), 1 deletions(-)
---
diff --git a/gtksourceview/gtksourcebuffer.c b/gtksourceview/gtksourcebuffer.c
index 7663a86..7797e7f 100644
--- a/gtksourceview/gtksourcebuffer.c
+++ b/gtksourceview/gtksourcebuffer.c
@@ -106,6 +106,17 @@
  * Custom language definition files can create their own context classes,
  * since the functions like gtk_source_buffer_iter_has_context_class() take
  * a string parameter as the context class.
+ *
+ * Each context class has an associated #GtkTextTag with the name
+ * <emphasis>gtksourceview:context-classes:&lt;name&gt;</emphasis>. For example to
+ * retrieve the #GtkTextTag for the string context class, one can write:
+ * |[
+ * GtkTextTagTable *tag_table;
+ * GtkTextTag *tag;
+ *
+ * tag_table = gtk_text_buffer_get_tag_table (buffer);
+ * tag = gtk_text_tag_table_lookup (tag_table, "gtksourceview:context-classes:string");
+ * ]|
  */
 
 /*
diff --git a/gtksourceview/gtksourcecontextengine.c b/gtksourceview/gtksourcecontextengine.c
index 7f3f504..0cfea5b 100644
--- a/gtksourceview/gtksourcecontextengine.c
+++ b/gtksourceview/gtksourcecontextengine.c
@@ -979,7 +979,11 @@ get_context_class_tag (GtkSourceContextEngine *ce,
 
        if (ret == NULL)
        {
-               ret = gtk_text_buffer_create_tag (ce->priv->buffer, NULL, NULL);
+               gchar *tag_name;
+
+               tag_name = g_strdup_printf ("gtksourceview:context-classes:%s", name);
+
+               ret = gtk_text_buffer_create_tag (ce->priv->buffer, tag_name, NULL);
                g_object_set_data_full (G_OBJECT (ret),
                                        TAG_CONTEXT_CLASS_NAME,
                                        g_strdup (name),
@@ -988,6 +992,8 @@ get_context_class_tag (GtkSourceContextEngine *ce,
                g_hash_table_insert (ce->priv->context_classes,
                                     g_strdup (name),
                                     ret);
+
+               g_free (tag_name);
        }
 
        return ret;