[pango/prevent-mixed-linkage] Add a check for mixed linkage

[Matthias Clasen <matthiasc src gnome org>]

commit 19992104201f198da7ce477410a606d7d0e4c7a5
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Jun 23 09:31:06 2022 -0400

    Add a check for mixed linkage
    
    Having both pango 1.x and pango 2 linked into
    the same process will cause trouble, because the
    type and function names conflict.
    
    Error out if we detect this situation.

 pango/pango-context.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
---
diff --git a/pango/pango-context.c b/pango/pango-context.c
index d5e73cfe5..9c0b81c10 100644
--- a/pango/pango-context.c
+++ b/pango/pango-context.c
@@ -80,11 +80,33 @@ pango_context_init (PangoContext *context)
   pango_font_description_set_size (context->font_desc, 12 * PANGO_SCALE);
 }
 
+static gboolean
+pango_has_mixed_deps (void)
+{
+  GModule *module;
+  gpointer func;
+  gboolean result = FALSE;
+
+  module = g_module_open (NULL, 0);
+
+  if (g_module_symbol (module, "pango_hb_font_new", &func))
+    result = TRUE;
+
+  g_module_close (module);
+
+  return result;
+}
+
 static void
 pango_context_class_init (PangoContextClass *klass)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
 
+ /* Put the check for mixed linkage here, for lack of a better place */
+  if (pango_has_mixed_deps ())
+    g_error ("Pango 2 symbols detected.\n"
+             "Using Pango 1.x and 2 in the same process is not supported.");
+
   object_class->finalize = pango_context_finalize;
 }