[indic] Special-case Kannada Ra,H,ZWJ sequence

Fixes https://github.com/behdad/harfbuzz/issues/435

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

@@ -691,6 +691,21 @@ initial_reordering_consonant_syllable (const hb_ot_shape_plan_t *plan,
   const indic_shape_plan_t *indic_plan = (const indic_shape_plan_t *) plan->data;
   hb_glyph_info_t *info = buffer->info;
 
+  /* https://github.com/behdad/harfbuzz/issues/435#issuecomment-335560167
+   * // For compatibility with legacy useage in Kannada,
+   * // Ra+h+ZWJ must behave like Ra+ZWJ+h...
+   */
+  if (buffer->props.script == HB_SCRIPT_KANNADA &&
+      start + 3 <= end &&
+      is_one_of (info[start  ], FLAG (OT_Ra)) &&
+      is_one_of (info[start+1], FLAG (OT_H)) &&
+      is_one_of (info[start+2], FLAG (OT_ZWJ)))
+  {
+    buffer->merge_clusters (start+1, start+3);
+    hb_glyph_info_t tmp = info[start+1];
+    info[start+1] = info[start+2];
+    info[start+2] = tmp;
+  }
 
   /* 1. Find base consonant:
    *

test/shaping/Makefile.am

@@ -61,6 +61,7 @@ TESTS = \
 	tests/indic-joiners.tests \
 	tests/indic-old-spec.tests \
 	tests/indic-pref-blocking.tests \
+	tests/indic-special-cases.tests \
 	tests/indic-syllable.tests \
 	tests/language-tags.tests \
 	tests/ligature-id.tests \

test/shaping/tests/indic-special-cases.tests

+fonts/sha1sum/3cae6bfe5b57c07ba81ddbd54c02fe4f3a1e3bf6.ttf::U+0CB0,U+0CCD,U+0C95:[gid1=0+1176|gid5=0+1161]
+fonts/sha1sum/3cae6bfe5b57c07ba81ddbd54c02fe4f3a1e3bf6.ttf::U+0CB0,U+200D,U+0CCD,U+0C95:[gid2=0+1334|gid6=0+358]
+fonts/sha1sum/3cae6bfe5b57c07ba81ddbd54c02fe4f3a1e3bf6.ttf::U+0CB0,U+0CCD,U+200D,U+0C95:[gid2=0+1334|gid6=0+358]