Remove final pause from Arabic shaper

Back in the old days, we used to apply 'calt' and 'cswh' in Arabic shaper,
with a pause in between.  Then we disabled the 'cswh' because Microsoft
disabled it, but forgot to remove the unnecessary pause.  Do that now.

This has the benefit that it fixes shaping with monbaiti from Windows 10.
In that version of that font, the lookups from 'calt' are duplicated in
'rclt', and Mongolian was changed to go through Universal Shaping Engine.
We still use the Arabic shaper for Mongolian.  With a pause after 'calt',
we were applying the duplicate lookups from 'calt' and 'rclt' twice.  It
happened to be the case that these lookups were NOT idempotent.  So we
were getting wrong shaping.  See thread "Windows 10 monbaiti.ttf upgrade
(5.01 -> 5.51) caused loss of diacritical marks when shaped with harfbuz"
on the mailing list.  This fixes that.

diff --git a/src/hb-ot-shape-complex-arabic.cc b/src/hb-ot-shape-complex-arabic.cc
index 6d9d093..8ab9a02 100644 (file)
--- a/src/hb-ot-shape-complex-arabic.cc
+++ b/src/hb-ot-shape-complex-arabic.cc
@@ -223,7 +223,6 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
     map->add_gsub_pause (arabic_fallback_shape);
 
   map->add_global_bool_feature (HB_TAG('c','a','l','t'));
-  map->add_gsub_pause (NULL);
 
   /* The spec includes 'cswh'.  Earlier versions of Windows
    * used to enable this by default, but testing suggests
@@ -233,6 +232,7 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
    * Note that IranNastaliq uses this feature extensively
    * to fixup broken glyph sequences.  Oh well...
    * Test case: U+0643,U+0640,U+0631. */
+  //map->add_gsub_pause (NULL);
   //map->add_global_bool_feature (HB_TAG('c','s','w','h'));
   map->add_global_bool_feature (HB_TAG('m','s','e','t'));
 }