Do NOT ignore Mongolian Free Variation Selectors during matching

Fixes https://github.com/behdad/harfbuzz/issues/234

src/hb-ot-layout-gsubgpos-private.hh

@@ -319,7 +319,7 @@ struct hb_apply_context_t :
       if (!c->check_glyph_property (&info, lookup_props))
 	return SKIP_YES;
 
-      if (unlikely (_hb_glyph_info_is_default_ignorable (&info) &&
+      if (unlikely (_hb_glyph_info_is_default_ignorable_and_not_fvs (&info) &&
 		    (ignore_zwnj || !_hb_glyph_info_is_zwnj (&info)) &&
 		    (ignore_zwj || !_hb_glyph_info_is_zwj (&info))))
 	return SKIP_MAYBE;

src/hb-ot-layout-private.hh

@@ -218,7 +218,8 @@ _next_syllable (hb_buffer_t *buffer, unsigned int start)
  * - General_Category: 5 bits.
  * - A bit each for:
  *   * Is it Default_Ignorable(); we have a modified Default_Ignorable().
- *   * Two free bits right now.
+ *   * Whether it's one of the three Mongolian Free Variation Selectors.
+ *   * One free bit right now.
  *
  * The high-byte has different meanings, switched by the Gen-Cat:
  * - For Mn,Mc,Me: the modified Combining_Class.
@@ -230,6 +231,7 @@ _next_syllable (hb_buffer_t *buffer, unsigned int start)
 enum hb_unicode_props_flags_t {
   UPROPS_MASK_GEN_CAT	= 0x001Fu,
   UPROPS_MASK_IGNORABLE	= 0x0020u,
+  UPROPS_MASK_FVS	= 0x0040u, /* MONGOLIAN FREE VARIATION SELECTOR 1..3 */
 
   /* If GEN_CAT=FORMAT, top byte masks: */
   UPROPS_MASK_Cf_ZWJ	= 0x0100u,
@@ -254,6 +256,15 @@ _hb_glyph_info_set_unicode_props (hb_glyph_info_t *info, hb_buffer_t *buffer)
       props |=  UPROPS_MASK_IGNORABLE;
       if (u == 0x200Cu) props |= UPROPS_MASK_Cf_ZWNJ;
       if (u == 0x200Du) props |= UPROPS_MASK_Cf_ZWJ;
+      /* Mongolian Free Variation Selectors need to be remembered
+       * because although we need to hide them like default-ignorables,
+       * they need to non-ignorable during shaping.  This is similar to
+       * what we do for joiners in Indic-like shapers, but since the
+       * FVSes are GC=Mn, we have use a separate bit to remember them.
+       * Fixes:
+       * https://github.com/behdad/harfbuzz/issues/234
+       */
+      if (unlikely (hb_in_range (u, 0x180Bu, 0x180Du))) props |= UPROPS_MASK_FVS;
     }
     else if (unlikely (HB_UNICODE_GENERAL_CATEGORY_IS_NON_ENCLOSING_MARK_OR_MODIFIER_SYMBOL (gen_cat)))
     {
@@ -349,7 +360,15 @@ static inline bool _hb_glyph_info_ligated (const hb_glyph_info_t *info);
 static inline hb_bool_t
 _hb_glyph_info_is_default_ignorable (const hb_glyph_info_t *info)
 {
-  return (info->unicode_props() & UPROPS_MASK_IGNORABLE) && !_hb_glyph_info_ligated (info);
+  return (info->unicode_props() & UPROPS_MASK_IGNORABLE) &&
+	 !_hb_glyph_info_ligated (info);
+}
+static inline hb_bool_t
+_hb_glyph_info_is_default_ignorable_and_not_fvs (const hb_glyph_info_t *info)
+{
+  return ((info->unicode_props() & (UPROPS_MASK_IGNORABLE|UPROPS_MASK_FVS))
+	  == UPROPS_MASK_IGNORABLE) &&
+	 !_hb_glyph_info_ligated (info);
 }
 
 static inline bool

src/hb-ot-shape-complex-arabic.cc

@@ -215,7 +215,7 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
   {
     bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);
     map->add_feature (arabic_features[i], 1, has_fallback ? F_HAS_FALLBACK : F_NONE);
-    map->add_gsub_pause (NULL);
+    //map->add_gsub_pause (NULL);
   }
 
   map->add_feature (HB_TAG('r','l','i','g'), 1, F_GLOBAL|F_HAS_FALLBACK);

test/shaping/tests/mongolian-variation-selector.tests

 fonts/sha1sum/37033cc5cf37bb223d7355153016b6ccece93b28.ttf::U+1826,U+180B,U+1826:[uni1826.E85E_ue.init1=0+599|uni1826.E856_ue.fina=2+750]
 fonts/sha1sum/ef86fe710cfea877bbe0dbb6946a1f88d0661031.ttf::U+1820,U+180B:[uni1820.E821_a.isol1=0+1199]
 fonts/sha1sum/bb29ce50df2bdba2d10726427c6b7609bf460e04.ttf::U+183A,U+1823,U+182E,U+182B,U+1822,U+1826,U+180B,U+1832,U+180B,U+1827,U+1837,U+0020,U+182D,U+182D,U+180B,U+0020,U+182D,U+180C,U+0020,U+182D,U+180D,U+200D,U+0020,U+182D,U+200D,U+182D,U+180B,U+200D,U+0020,U+182D,U+180C,U+200D,U+0020,U+182D,U+180D,U+200D,U+0020,U+200D,U+182D,U+200D,U+200D,U+182D,U+180B,U+200D,U+0020,U+200D,U+182D,U+180C,U+200D,U+0020,U+200D,U+182D,U+180D,U+200D,U+0020,U+200D,U+182D,U+200D,U+182D,U+180B,U+0020,U+200D,U+182D,U+180C,U+0020,U+1820,U+200C,U+182D,U+1820,U+1837,U+0020,U+1830,U+1824,U+1837,U+200D,U+200D,U+182D,U+1820,U+200D,U+0020,U+200D,U+182D,U+1824,U+182F,U+1822,U+0020,U+182A,U+1820,U+1822,U+182D,U+180E,U+1820,U+202F,U+1836,U+1822,U+1828:[uni183A1823.E971_ko.init=0+950|uni182E.E904_m.medi=2+400|uni182B1822.E8A6_pi.medi=3+1150|uni1826.E854_ue.medi1=5+1100|uni1832.E916_t.medi1=7+1000|uni1827.E85C_ee.medi=9+750|uni1837.E931_r.fina=10+750|space=11+500|uni182D.E8E2_g.init=12+1000|uni182D.E8E8_g.fina1=13+1250|space=15+500|uni182D.EA1B_g.isol2=16+1000|space=18+500|uni182D.EA1E_g.init3=19+650|space=19+0|space=22+500|uni182D.E8E2_g.init=23+1000|space=23+0|uni182D.E8E5_g.medi1=25+800|space=25+0|space=28+500|uni182D.EA1D_g.init2=29+950|space=29+0|space=32+500|uni182D.EA1E_g.init3=33+650|space=33+0|space=36+500|space=36+0|uni182D.E8E4_g.medi=38+800|space=38+0|space=38+0|uni182D.E8E5_g.medi1=41+800|space=41+0|space=44+500|space=44+0|uni182D.E8E6_g.medi2=46+650|space=46+0|space=49+500|space=49+0|uni182D.E8E6_g.medi2=51+650|space=51+0|space=54+500|space=54+0|uni182D.E8E4_g.medi=56+800|space=56+0|uni182D.E8E8_g.fina1=58+1250|space=60+500|space=60+0|uni182D.E8E9_g.fina2=62+1050|space=64+500|uni1820.E820_a.isol=65+1550|space=65+0|uni182D.E8E2_g.init=67+1000|uni1820.E823_a.medi=68+400|uni1837.E931_r.fina=69+750|space=70+500|uni1830.E90B_s.init=71+850|uni1824.E844_u.medi=72+600|uni1837.E930_r.medi=73+600|space=73+0|space=73+0|uni182D.E8E5_g.medi1=76+800|uni1820.E823_a.medi=77+400|space=77+0|space=79+500|space=79+0|uni182D.E8E5_g.medi1=81+800|uni1824.E844_u.medi=82+600|uni182F.E908_l.medi=83+400|uni1822.E837_i.fina=84+600|space=85+500|uni182A1820.E875_ba.init=86+1000|uni1822.E836_i.medi2=88+1000|uni182D.E8E8_g.fina1=89+1250|space=90+0|uni1820.E827_a.fina2=91+600|uni202F.nobreak=92+500|uni1836.E92B_y.init1=93+500|uni1822.E834_i.medi=94+500|uni1828.E866_n.fina=95+850]
+fonts/sha1sum/a34a7b00f22ffb5fd7eef6933b81c7e71bc2cdfb.ttf::U+180A,U+1868,U+180A,U+1868,U+180B,U+180A,U+1868,U+180C,U+180A,U+1868,U+180D,U+180A:[gid1=0+268|gid10=1+778|gid1=2+268|gid9=3+575|gid1=5+268|gid10=6+778|gid1=8+268|gid8=9+575|gid1=11+268]