[indic] Fix https://github.com/behdad/harfbuzz/issues/478

src/hb-ot-shape-complex-indic-private.hh

@@ -132,7 +132,7 @@ enum indic_syllabic_category_t {
   INDIC_SYLLABIC_CATEGORY_NUMBER_JOINER			= OT_PLACEHOLDER, /* Don't care. */
   INDIC_SYLLABIC_CATEGORY_PURE_KILLER			= OT_M, /* Is like a vowel matra. */
   INDIC_SYLLABIC_CATEGORY_REGISTER_SHIFTER		= OT_RS,
-  INDIC_SYLLABIC_CATEGORY_SYLLABLE_MODIFIER		= OT_M, /* Misc Khmer signs. */
+  INDIC_SYLLABIC_CATEGORY_SYLLABLE_MODIFIER		= OT_SM,
   INDIC_SYLLABIC_CATEGORY_TONE_LETTER			= OT_X,
   INDIC_SYLLABIC_CATEGORY_TONE_MARK			= OT_N,
   INDIC_SYLLABIC_CATEGORY_VIRAMA			= OT_H,

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

@@ -200,6 +200,14 @@ set_indic_properties (hb_glyph_info_t &info)
     cat = OT_Symbol;
     ASSERT_STATIC ((int) INDIC_SYLLABIC_CATEGORY_AVAGRAHA == OT_Symbol);
   }
+  else if (unlikely (hb_in_range (u, 0x17CDu, 0x17D1u) ||
+		     u == 0x17CBu || u == 0x17D3u || u == 0x17DDu)) /* Khmer Various signs */
+  {
+    /* These can occur mid-syllable (eg. before matras), even though Unicode marks them as Syllable_Modifier. */
+    cat = OT_M;
+    pos = POS_ABOVE_C;
+  }
+
   else if (unlikely (u == 0x17C6u)) cat = OT_N; /* Khmer Bindu doesn't like to be repositioned. */
   else if (unlikely (hb_in_range<hb_codepoint_t> (u, 0x2010u, 0x2011u)))
 				    cat = OT_PLACEHOLDER;

test/shaping/Makefile.am

@@ -59,6 +59,7 @@ TESTS = \
 	tests/indic-joiners.tests \
 	tests/indic-old-spec.tests \
 	tests/indic-pref-blocking.tests \
+	tests/indic-syllable.tests \
 	tests/language-tags.tests \
 	tests/ligature-id.tests \
 	tests/mark-filtering-sets.tests \

test/shaping/tests/indic-syllable.tests

@@ -0,0 +1 @@
+fonts/sha1sum/54674a3111d209fb6be0ed31745314b7a8d2c244.ttf::U+0BA4,U+0BCD,U+00B3:[taprehalftamil=0+1509|uni00B3=2+674]