[typelib] Clean up dlopen handling

It's was busted that g_typelib_new_* does the dlopen() since that caused
g-ir-compiler to load the modules even though it wasn't going to do
anything with them.

Instead, change things so that g_module_symbol does the dlopen on-demand.
Remove the extra dlopen(NULL) inside girepository.c, we had another
already in gtypelib.c.

Thanks to Owen Taylor for suggesting this approach.

girepository.c

@@ -363,9 +363,6 @@ register_internal (GIRepository *repository,
       g_hash_table_insert (repository->priv->typelibs, key, (void *)typelib);
     }
 
-  if (typelib->modules == NULL)
-    typelib->modules = g_list_append(typelib->modules, g_module_open (NULL, 0));
-
   return namespace;
 }
 

gtypelib.c

@@ -1946,21 +1946,20 @@ g_typelib_error_quark (void)
   return quark;
 }
 
-static inline void
-_g_typelib_init (GTypelib *typelib)
+static void
+_g_typelib_do_dlopen (GTypelib *typelib)
 {
   Header *header;
+  const char *shlib_str;
   
   header = (Header *) typelib->data;
-  if (header->shared_library)
-    {
-      const gchar *shlib_str;
-      GModule *app_module = NULL;
-
-      shlib_str = g_typelib_get_string (typelib, header->shared_library);
   /* note that NULL shlib means to open the main app, which is allowed */
+  if (header->shared_library)
+    shlib_str = g_typelib_get_string (typelib, header->shared_library);
+  else
+    shlib_str = NULL;
 
-      if (shlib_str != NULL)
+  if (shlib_str != NULL && shlib_str[0] != '\0')
     {
       gchar **shlibs;
       gint i;
@@ -2018,16 +2017,30 @@ _g_typelib_init (GTypelib *typelib)
 
       g_strfreev (shlibs);
     }
-
-        /* we should make sure the app_module in the end of list so that
-         * it's last symbol source when loading any symbols from modules.
-         * See comments in g_typelib_symbol */
-        app_module = g_module_open (NULL, G_MODULE_BIND_LAZY);
-        if (app_module)
-          typelib->modules = g_list_append (typelib->modules, app_module);
+  else
+    {
+      /* If there's no shared-library entry for this module, assume that
+       * the module is for the application.  Some of the hand-written .gir files
+       * in gobject-introspection don't have shared-library entries, but no one
+       * is really going to be calling g_module_symbol on them either.
+       */
+      GModule *module = g_module_open (NULL, 0);
+      if (module == NULL)
+        g_warning ("gtypelib.c: Failed to g_module_open (NULL): %s", g_module_error ());
+      else
+        typelib->modules = g_list_prepend (typelib->modules, module);
     }
 }
 
+static inline void
+_g_typelib_ensure_open (GTypelib *typelib)
+{
+  if (typelib->open_attempted)
+    return;
+  typelib->open_attempted = TRUE;
+  _g_typelib_do_dlopen (typelib);
+}
+
 /**
  * g_typelib_new_from_memory:
  * @memory: address of memory chunk containing the typelib
@@ -2049,7 +2062,7 @@ g_typelib_new_from_memory (guchar *memory, gsize len)
   meta->len = len;
   meta->owns_memory = TRUE;
   meta->modules = NULL;
-  _g_typelib_init (meta);
+
   return meta;
 }
 
@@ -2072,7 +2085,7 @@ g_typelib_new_from_const_memory (const guchar *memory, gsize len)
   meta->len = len;
   meta->owns_memory = FALSE;
   meta->modules = NULL;
-  _g_typelib_init (meta);
+
   return meta;
 }
 
@@ -2094,7 +2107,7 @@ g_typelib_new_from_mapped_file (GMappedFile *mfile)
   meta->owns_memory = FALSE;
   meta->data = (guchar *) g_mapped_file_get_contents (mfile);
   meta->len = g_mapped_file_get_length (mfile);
-  _g_typelib_init (meta);
+
   return meta;
 }
 
@@ -2141,20 +2154,18 @@ g_typelib_symbol (GTypelib *typelib, const char *symbol_name, gpointer *symbol)
 {
   GList *l;
   
+  _g_typelib_ensure_open (typelib);
+
   /*
-   * We want to be able to add symbols to an app or an auxiliary
-   * library to fill in gaps in an introspected library. However,
-   * normally we would only look for symbols in the main library
-   * (the first items in typelib->modules).
+   * The reason for having multiple modules dates from gir-repository
+   * when it was desired to inject code (accessors, etc.) into an
+   * existing library.  In that situation, the first module listed
+   * will be the custom one, which overrides the main one.  A bit
+   * inefficient, but the problem will go away when gir-repository
+   * does.
    * 
-   * A more elaborate solution is probably possible, but as a
-   * simple approach for now, if we fail to find a symbol we look
-   * for it in the global module (the last item in type->modules).
-   *
-   * This would not be very efficient if it happened often, since
-   * we always do the failed lookup above first, but very few
-   * symbols should be outside of the main libraries in
-   * typelib->modules so it doesn't matter.
+   * For modules with no shared library, we dlopen'd the current
+   * process above.  
    */
   for (l = typelib->modules; l; l = l->next)
     {

gtypelib.h

@@ -1021,6 +1021,7 @@ struct _GTypelib {
   gboolean owns_memory;
   GMappedFile *mfile;
   GList *modules;
+  gboolean open_attempted;
 };
 
 DirEntry *g_typelib_get_dir_entry (GTypelib *typelib,