Add a new #GtkSourceCompletionProvider to the completion object. This will add a reference provider, so make sure to unref your own copy when you no longer need it.
a #GtkSourceCompletionProvider.
true if provider was successfully added, otherwise if error is provided, it will be set with the error and false is returned.
ErrorWrap
Add a new #GtkSourceCompletionProvider to the completion object. This will add a reference provider, so make sure to unref your own copy when you no longer need it.