girepository: Merge overrides with the regular search path

This reverts commit e81c4681cc88a00fcd841c5a68d860d3714b55d7

The GI_TYPELIB_PATH envvar will still allow overriding the default
typelib dir (based on gobject-introspection libdir), but applications
will have the last say about typelib lookup directories. The resulting
lookup order is now:

- Paths added through g_irepository_prepend_search_path()
- Paths in GI_TYPELIB_PATH
- The default gobject introspection lookup dir

This makes g_irespository_prepend_search_path() work as announced
despite environment variables. If any application was relying on
GI_TYPELIB_PATH overriding the paths of this function call (for e.g.
make check, or to be able to run code inside the project tree), it
is encouraged to set up a similar envvar for their application specific
lookup dir, or perform this override through other means.

https://bugzilla.gnome.org/show_bug.cgi?id=765735

girepository.c

@@ -46,7 +46,6 @@
 
 static GIRepository *default_repository = NULL;
 static GSList *search_path = NULL;
-static GSList *override_search_path = NULL;
 
 struct _GIRepositoryPrivate
 {
@@ -163,7 +162,6 @@ init_globals (void)
       type_lib_path_env = g_getenv ("GI_TYPELIB_PATH");
 
       search_path = NULL;
-      override_search_path = NULL;
       if (type_lib_path_env)
         {
           gchar **custom_dirs;
@@ -174,7 +172,7 @@ init_globals (void)
           d = custom_dirs;
           while (*d)
             {
-              override_search_path = g_slist_prepend (override_search_path, *d);
+              search_path = g_slist_prepend (search_path, *d);
               d++;
             }
 
@@ -182,9 +180,6 @@ init_globals (void)
           g_free (custom_dirs);
         }
 
-      if (override_search_path != NULL)
-        override_search_path = g_slist_reverse (override_search_path);
-
       libdir = GOBJECT_INTROSPECTION_LIBDIR;
 
       typelib_dir = g_build_filename (libdir, "girepository-1.0", NULL);
@@ -227,23 +222,6 @@ g_irepository_get_search_path (void)
   return search_path;
 }
 
-static GSList *
-build_search_path_with_overrides (void)
-{
-  GSList *result;
-
-  init_globals ();
-
-  if (override_search_path != NULL)
-    {
-      result = g_slist_copy (override_search_path);
-      g_slist_last (result)->next = g_slist_copy (search_path);
-    }
-  else
-    result = g_slist_copy (search_path);
-  return result;
-}
-
 static char *
 build_typelib_key (const char *name, const char *source)
 {
@@ -1394,13 +1372,11 @@ g_irepository_enumerate_versions (GIRepository *repository,
 			 const gchar  *namespace_)
 {
   GList *ret = NULL;
-  GSList *search_path;
   GSList *candidates, *link;
   const gchar *loaded_version;
 
-  search_path = build_search_path_with_overrides ();
+  init_globals ();
   candidates = enumerate_namespace_versions (namespace_, search_path);
-  g_slist_free (search_path);
 
   for (link = candidates; link; link = link->next)
     {
@@ -1563,13 +1539,11 @@ g_irepository_require (GIRepository  *repository,
 		       GIRepositoryLoadFlags flags,
 		       GError       **error)
 {
-  GSList *search_path;
   GITypelib *typelib;
 
-  search_path = build_search_path_with_overrides ();
+  init_globals ();
   typelib = require_internal (repository, namespace, version, flags,
 			      search_path, error);
-  g_slist_free (search_path);
 
   return typelib;
 }