Another try to fix Mongolian free variation selectors

This reverts bf029281 and fixes it properly.  That commit
was not enough as it was only inheriting the shaping_action
for prev_action, but not curr_action.

Micro-test added.

https://code.google.com/p/chromium/issues/detail?id=393896

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

@@ -225,8 +225,6 @@ arabic_joining (hb_buffer_t *buffer)
   unsigned int count = buffer->len;
   unsigned int prev = (unsigned int) -1, state = 0;
 
-  HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
-
   /* Check pre-context */
   if (!(buffer->flags & HB_BUFFER_FLAG_BOT))
     for (unsigned int i = 0; i < buffer->context_len[0]; i++)
@@ -253,8 +251,7 @@ arabic_joining (hb_buffer_t *buffer)
     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 
     if (entry->prev_action != NONE && prev != (unsigned int) -1)
-      for (; prev < i; prev++)
-	buffer->info[prev].arabic_shaping_action() = entry->prev_action;
+      buffer->info[prev].arabic_shaping_action() = entry->prev_action;
 
     buffer->info[i].arabic_shaping_action() = entry->curr_action;
 
@@ -275,9 +272,17 @@ arabic_joining (hb_buffer_t *buffer)
 	buffer->info[prev].arabic_shaping_action() = entry->prev_action;
       break;
     }
+}
 
-
-  HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
+static void
+mongolian_variation_selectors (hb_buffer_t *buffer)
+{
+  /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */
+  unsigned int count = buffer->len;
+  hb_glyph_info_t *info = buffer->info;
+  for (unsigned int i = 1; i < count; i++)
+    if (unlikely (hb_in_range (info[i].codepoint, 0x180Bu, 0x180Du)))
+      info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
 }
 
 static void
@@ -285,12 +290,19 @@ setup_masks_arabic (const hb_ot_shape_plan_t *plan,
 		    hb_buffer_t              *buffer,
 		    hb_font_t                *font HB_UNUSED)
 {
+  HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
+
   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 
   arabic_joining (buffer);
+  if (plan->props.script == HB_SCRIPT_MONGOLIAN)
+    mongolian_variation_selectors (buffer);
+
   unsigned int count = buffer->len;
   for (unsigned int i = 0; i < count; i++)
     buffer->info[i].mask |= arabic_plan->mask_array[buffer->info[i].arabic_shaping_action()];
+
+  HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
 }
 
 

src/hb-unicode-private.hh

@@ -122,8 +122,9 @@ HB_UNICODE_FUNCS_IMPLEMENT_CALLBACKS_SIMPLE
   static inline hb_bool_t
   is_variation_selector (hb_codepoint_t unicode)
   {
+    /* U+180B..180D MONGOLIAN FREE VARIATION SELECTORs are handled in the
+     * Arabic shaper.  No need to match them here. */
     return unlikely (hb_in_ranges (unicode,
-				   0x180Bu, 0x180Du, /* MONGOLIAN FREE VARIATION SELECTOR ONE..THREE */
 				   0xFE00u, 0xFE0Fu, /* VARIATION SELECTOR-1..16 */
 				   0xE0100u, 0xE01EFu));  /* VARIATION SELECTOR-17..256 */
   }

test/shaping/fonts/sha1sum/MANIFEST

@@ -3,4 +3,5 @@
 4cce528e99f600ed9c25a2b69e32eb94a03b4ae8.ttf
 d629e7fedc0b350222d7987345fe61613fa3929a.ttf
 e207635780b42f898d58654b65098763e340f5c7.ttf
+ef86fe710cfea877bbe0dbb6946a1f88d0661031.ttf
 f499fbc23865022234775c43503bba2e63978fe1.ttf

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

@@ -1 +1,2 @@
 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]