[pango/fix-another-crash] itemize: Work around gtk2 brokenness

[Matthias Clasen <matthiasc src gnome org>]

commit 279bd5256b17ed68d50fbaaf7df60f189de33c96
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jun 10 11:36:24 2020 -0400

    itemize: Work around gtk2 brokenness
    
    GTK 2 apparently manages to call pango_itemize_with_base_dir
    with a non-zero length for a string that contains 0 characters.
    That in turn causes pango_log2vis_get_embedding_levels to
    return NULL, and things go downhill from there.
    
    A test is included.
    
    Fixes: #480

 pango/pango-context.c |  2 +-
 tests/testmisc.c      | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
---
diff --git a/pango/pango-context.c b/pango/pango-context.c
index 7772878f..bebe804a 100644
--- a/pango/pango-context.c
+++ b/pango/pango-context.c
@@ -1566,7 +1566,7 @@ pango_itemize_with_base_dir (PangoContext      *context,
   g_return_val_if_fail (length >= 0, NULL);
   g_return_val_if_fail (length == 0 || text != NULL, NULL);
 
-  if (length == 0)
+  if (length == 0 || g_utf8_strlen (text, length) == 0)
     return NULL;
 
   itemize_state_init (&state, context, text, base_dir, start_index, length,
diff --git a/tests/testmisc.c b/tests/testmisc.c
index a078944d..f5583cab 100644
--- a/tests/testmisc.c
+++ b/tests/testmisc.c
@@ -41,12 +41,26 @@ test_shape_tab_crash (void)
   g_object_unref (context);
 }
 
+/* Test that itemizing a string with 0 characters works
+ */
+static void
+test_itemize_empty_crash (void)
+{
+  PangoContext *context;
+
+  context = pango_font_map_create_context (pango_cairo_font_map_get_default ());
+  pango_itemize_with_base_dir (context, PANGO_DIRECTION_LTR, "", 0, 1, NULL, NULL);
+
+  g_object_unref (context);
+}
+
 int
 main (int argc, char *argv[])
 {
   g_test_init (&argc, &argv, NULL);
 
   g_test_add_func ("/layout/shape-tab-crash", test_shape_tab_crash);
+  g_test_add_func ("/layout/itemize-empty-crash", test_itemize_empty_crash);
 
   return g_test_run ();
 }