[indic] Handle Avagraha

It can come either at the end(ish!) of the syllable, or independently.
When independent, it accepts a few bits and pieces.

src/hb-ot-shape-complex-indic-machine.rl

@@ -56,6 +56,7 @@ Coeng = 14;
 Repha = 15;
 Ra    = 16;
 CM    = 17;
+Avag  = 18;
 
 c = (C | Ra)CM*;		# is_consonant
 n = ((ZWNJ?.RS)? (N.N?)?);	# is_consonant_modifier
@@ -66,7 +67,7 @@ reph = (Ra H | Repha);		# possible reph
 cn = c.ZWJ?.n?;
 forced_rakar = ZWJ H ZWJ Ra;
 matra_group = z{0,3}.M.N?.(H | forced_rakar)?;
-syllable_tail =  (Coeng (cn|V))? (SM.ZWNJ?)? (VD VD?)?;
+syllable_tail =  (Coeng (cn|V))? (Avag.N?)? (SM.ZWNJ?)? (VD VD?)?;
 place_holder = NBSP | DOTTEDCIRCLE;
 halant_group = (z?.h.(ZWJ.N?)?);
 final_halant_group = halant_group | h.ZWNJ;
@@ -76,6 +77,7 @@ halant_or_matra_group = (final_halant_group | (h.ZWJ)? matra_group{0,4});
 consonant_syllable =	Repha? (cn.halant_group){0,4} cn A? halant_or_matra_group? syllable_tail;
 vowel_syllable =	reph? V.n? (ZWJ | (halant_group.cn){0,4} halant_or_matra_group? syllable_tail);
 standalone_cluster =	reph? place_holder.n? (halant_group.cn){0,4} halant_or_matra_group? syllable_tail;
+avagraha_cluster = 	Avag.N? (SM.ZWNJ?)? (VD VD?)?;
 broken_cluster =	reph? n? (halant_group.cn){0,4} halant_or_matra_group syllable_tail;
 other =			any;
 
@@ -83,6 +85,7 @@ main := |*
 	consonant_syllable	=> { found_syllable (consonant_syllable); };
 	vowel_syllable		=> { found_syllable (vowel_syllable); };
 	standalone_cluster	=> { found_syllable (standalone_cluster); };
+	avagraha_cluster	=> { found_syllable (avagraha_cluster); };
 	broken_cluster		=> { found_syllable (broken_cluster); };
 	other			=> { found_syllable (non_indic_cluster); };
 *|;

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

@@ -59,7 +59,8 @@ enum indic_category_t {
   OT_Coeng,
   OT_Repha,
   OT_Ra, /* Not explicitly listed in the OT spec, but used in the grammar. */
-  OT_CM
+  OT_CM,
+  OT_Avag
 };
 
 /* Visual positions in a syllable from left to right. */
@@ -93,7 +94,7 @@ enum indic_position_t {
 enum indic_syllabic_category_t {
   INDIC_SYLLABIC_CATEGORY_OTHER			= OT_X,
 
-  INDIC_SYLLABIC_CATEGORY_AVAGRAHA		= OT_X,
+  INDIC_SYLLABIC_CATEGORY_AVAGRAHA		= OT_Avag,
   INDIC_SYLLABIC_CATEGORY_BINDU			= OT_SM,
   INDIC_SYLLABIC_CATEGORY_CONSONANT		= OT_C,
   INDIC_SYLLABIC_CATEGORY_CONSONANT_DEAD	= OT_C,

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

@@ -249,7 +249,7 @@ set_indic_properties (hb_glyph_info_t &info)
   {
     pos = matra_position (u, pos);
   }
-  else if (cat == OT_SM || cat == OT_VD)
+  else if (cat == OT_SM || cat == OT_VD || cat == OT_Avag)
   {
     pos = POS_SMVD;
   }
@@ -584,6 +584,7 @@ enum syllable_type_t {
   consonant_syllable,
   vowel_syllable,
   standalone_cluster,
+  avagraha_cluster,
   broken_cluster,
   non_indic_cluster,
 };
@@ -1081,6 +1082,16 @@ initial_reordering_broken_cluster (const hb_ot_shape_plan_t *plan,
   initial_reordering_standalone_cluster (plan, face, buffer, start, end);
 }
 
+static void
+initial_reordering_avagraha_cluster (const hb_ot_shape_plan_t *plan HB_UNUSED,
+				     hb_face_t *face HB_UNUSED,
+				     hb_buffer_t *buffer HB_UNUSED,
+				     unsigned int start HB_UNUSED, unsigned int end HB_UNUSED)
+{
+  /* Nothing to do right now.  If we ever switch to using the output
+   * buffer in the reordering process, we'd need to next_glyph() here. */
+}
+
 static void
 initial_reordering_non_indic_cluster (const hb_ot_shape_plan_t *plan HB_UNUSED,
 				      hb_face_t *face HB_UNUSED,
@@ -1103,6 +1114,7 @@ initial_reordering_syllable (const hb_ot_shape_plan_t *plan,
   case consonant_syllable:	initial_reordering_consonant_syllable (plan, face, buffer, start, end); return;
   case vowel_syllable:		initial_reordering_vowel_syllable     (plan, face, buffer, start, end); return;
   case standalone_cluster:	initial_reordering_standalone_cluster (plan, face, buffer, start, end); return;
+  case avagraha_cluster:	initial_reordering_avagraha_cluster   (plan, face, buffer, start, end); return;
   case broken_cluster:		initial_reordering_broken_cluster     (plan, face, buffer, start, end); return;
   case non_indic_cluster:	initial_reordering_non_indic_cluster  (plan, face, buffer, start, end); return;
   }

test/shaping/texts/in-tree/shaper-indic/indic/script-devanagari/misc/misc.txt

@@ -30,3 +30,4 @@
 र्अ्‍
 र्आ्र्
 क‌ि
+ऽं

test/shaping/texts/in-tree/shaper-indic/indic/script-telugu/misc/misc.txt

@@ -9,3 +9,4 @@
 క్ష
 క్ష్
 క్ష్ణ
+ఽం