Form cluster for Emoji sub-region tag sequences

Fixes https://github.com/harfbuzz/harfbuzz/issues/1556

src/hb-ot-shape.cc

@@ -428,6 +428,19 @@ hb_set_unicode_props (hb_buffer_t *buffer)
 	_hb_glyph_info_set_continuation (&info[i]);
       }
     }
+    /* Or part of the Other_Grapheme_Extend that is not marks.
+     * As of Unicode 11 that is just:
+     *
+     * 200C          ; Other_Grapheme_Extend # Cf       ZERO WIDTH NON-JOINER
+     * FF9E..FF9F    ; Other_Grapheme_Extend # Lm   [2] HALFWIDTH KATAKANA VOICED SOUND MARK..HALFWIDTH KATAKANA SEMI-VOICED SOUND MARK
+     * E0020..E007F  ; Other_Grapheme_Extend # Cf  [96] TAG SPACE..CANCEL TAG
+     *
+     * ZWNJ is special, we decide about that seprately.  Ignore Katakana.
+     * Tags are used for Emoji sub-region flag sequences:
+     * https://github.com/harfbuzz/harfbuzz/issues/1556
+     */
+    else if (unlikely (hb_in_range<hb_codepoint_t> (info[i].codepoint, 0xE0020u, 0xE007Fu)))
+      _hb_glyph_info_set_continuation (&info[i]);
   }
 }
 

test/shaping/data/in-house/tests/cluster.tests

@@ -1,2 +1,3 @@
 ../fonts/4fac3929fc3332834e93673780ec0fe94342d193.ttf:--cluster-level=2:U+0078,U+030A,U+0058,U+030A:[gid2=0+1083|gid3=1@-1132,-8+0|gid1=2+1200|gid3=3@-1190,349+0]
 ../fonts/43ef465752be9af900745f72fe29cb853a1401a5.ttf:--cluster-level=1:U+05D4,U+05B7,U+05E9,U+05BC,U+05C1,U+05B8,U+05DE,U+05B4,U+05DD:[uni05DD=8+1359|uni05B4=7@111,0+0|uni05DE=6+1391|uni05B8=5+0|uni05BC=3+0|uni05C1=3+0|uni05E9=2+1451|uni05B7=1@28,0+0|uni05D4=0+1338]
+../fonts/8d9c4b193808b8bde94389ba7831c1fc6f9e794e.ttf::U+1F3F4,U+E0067,U+E0062,U+E0077,U+E006C,U+E0073,U+E007F:[.notdef=0+1229|space=0+0|space=0+0|space=0+0|space=0+0|space=0+0|space=0+0]