From 171f1804dc76dfcc2857e809d49a2290b15612c4 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@debian.org>
Date: Fri, 29 Dec 2023 16:15:10 +0000
Subject: [PATCH] girepository: Skip GIRepository versions not matching
 GIRepository-2.0

A few applications such as gnome-music load the GIRepository typelib
and use it to adjust their search paths.

GLib 2.79.x now provides libgirepository-2.0.so.0 (GIRepository-3.0),
but each OS distribution is likely to have a transitional period during
which GLib's libgirepository-2.0.so.0 has become available, but bindings
like PyGI and gjs are still linked to gobject-introspection's
libgirepository-1.0.so.1 (GIRepository-2.0).

During this transitional period, interpreted languages that load the
GIRepository namespace could get the "wrong" version, which will result
in adjusting a search path that will not actually affect the language
binding's typelib lookup, and could also lead to symbol and type-system
conflicts.

We can avoid this collision by making GLib's GIRepository library refuse
to load versions of the GIRepository typelib that are not 3.0, and
similarly making gobject-introspection's GIRepository library refuse to
load typelib versions that are not 2.0. A relatively neat way to achieve
that is to make each version behave as if the other one doesn't exist.

Signed-off-by: Simon McVittie <smcv@debian.org>
---
 girepository/girepository.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/girepository/girepository.c b/girepository/girepository.c
index a0754f456..12eaf366f 100644
--- a/girepository/girepository.c
+++ b/girepository/girepository.c
@@ -54,6 +54,13 @@
  * and the g_irepository_prepend_search_path() calls.
  */
 
+/* The namespace and version corresponding to libgirepository itself, so
+ * that we can refuse to load typelibs corresponding to the newer,
+ * incompatible version of this same library in GLib. */
+#define GIREPOSITORY_TYPELIB_NAME "GIRepository"
+#define GIREPOSITORY_TYPELIB_VERSION "2.0"
+#define GIREPOSITORY_TYPELIB_FILENAME \
+  GIREPOSITORY_TYPELIB_NAME "-" GIREPOSITORY_TYPELIB_VERSION ".typelib"
 
 static GIRepository *default_repository = NULL;
 static GSList *typelib_search_path = NULL;
@@ -1255,6 +1262,16 @@ find_namespace_version (const gchar  *namespace,
   GMappedFile *mfile = NULL;
   char *fname;
 
+  if (g_str_equal (namespace, GIREPOSITORY_TYPELIB_NAME) &&
+      !g_str_equal (version, GIREPOSITORY_TYPELIB_VERSION))
+    {
+      g_debug ("Ignoring %s-%s.typelib because this libgirepository "
+              "corresponds to %s-%s",
+               namespace, version,
+               namespace, GIREPOSITORY_TYPELIB_VERSION);
+      return NULL;
+    }
+
   fname = g_strdup_printf ("%s-%s.typelib", namespace, version);
 
   for (ldir = search_path; ldir; ldir = ldir->next)
@@ -1406,6 +1423,15 @@ enumerate_namespace_versions (const gchar *namespace,
 	      const char *name_end;
 	      int major, minor;
 
+	     if (g_str_equal (namespace, GIREPOSITORY_TYPELIB_NAME) &&
+		 !g_str_equal (entry, GIREPOSITORY_TYPELIB_FILENAME))
+	       {
+		 g_debug ("Ignoring %s because this libgirepository "
+			  "corresponds to %s",
+			  entry, GIREPOSITORY_TYPELIB_FILENAME);
+		 continue;
+	       }
+
 	      name_end = strrchr (entry, '.');
 	      last_dash = strrchr (entry, '-');
 	      version = g_strndup (last_dash+1, name_end-(last_dash+1));
-- 
GitLab