[indic] Allow double-halant in old-spec Devanagari

Fixes https://github.com/harfbuzz/harfbuzz/issues/1071

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

@@ -667,10 +667,10 @@ initial_reordering_consonant_syllable (const hb_ot_shape_plan_t *plan,
    * last consonant.
    *
    * Reports suggest that in some scripts Uniscribe does this only if there
-   * is *not* a Halant after last consonant already (eg. Kannada), while it
-   * does it unconditionally in other scripts (eg. Malayalam, Bengali).  We
-   * don't currently know about other scripts, so we whitelist Malayalam and
-   * Bengali for now.
+   * is *not* a Halant after last consonant already.  We know that is the
+   * case for Kannada, while it reorders unconditionally in other scripts,
+   * eg. Malayalam, Bengali, and Devanagari.  We don't currently know about
+   * other scripts, so we whitelist Malayalam, Bengali, and Devanagari.
    *
    * Kannada test case:
    * U+0C9A,U+0CCD,U+0C9A,U+0CCD
@@ -681,15 +681,21 @@ initial_reordering_consonant_syllable (const hb_ot_shape_plan_t *plan,
    * U+0D38,U+0D4D,U+0D31,U+0D4D,U+0D31,U+0D4D
    * With lohit-ttf-20121122/Lohit-Malayalam.ttf
    *
-   * Bengali test case
+   * Bengali test case:
    * U+0998,U+09CD,U+09AF,U+09CD
    * With Windows XP vrinda.ttf
    * https://github.com/harfbuzz/harfbuzz/issues/1073
+   *
+   * Devanagari test case:
+   * U+091F,U+094D,U+0930,U+094D
+   * With chandas.ttf
+   * https://github.com/harfbuzz/harfbuzz/issues/1071
    */
   if (indic_plan->is_old_spec)
   {
     bool disallow_double_halants = buffer->props.script != HB_SCRIPT_MALAYALAM &&
-				   buffer->props.script != HB_SCRIPT_BENGALI;
+				   buffer->props.script != HB_SCRIPT_BENGALI &&
+				   buffer->props.script != HB_SCRIPT_DEVANAGARI;
     for (unsigned int i = base + 1; i < end; i++)
       if (info[i].indic_category() == OT_H)
       {

test/shaping/data/in-house/tests/indic-old-spec.tests

 ../fonts/57a9d9f83020155cbb1d2be1f43d82388cbecc88.ttf::U+0C9A,U+0CCD,U+0C9A,U+0CCD:[U0C9A_U0CCD.haln=0+1066|U0C9A_0CCD.blwf=0+0]
 ../fonts/270b89df543a7e48e206a2d830c0e10e5265c630.ttf::U+0D38,U+0D4D,U+0D31,U+0D4D,U+0D31,U+0D4D:[glyph201=0+1183|U0D4D=0+0]
+../fonts/b722a7d09e60421f3efbc706ad348ab47b88567b.ttf::U+091F,U+094D,U+0930,U+094D,U+0020:[Tra=0+550|virAma=0@-73,-110+0|space=4+500]
+../fonts/b722a7d09e60421f3efbc706ad348ab47b88567b.ttf::U+091F,U+094D,U+0930,U+0942:[Tra=0+550|UT=0@42,-150+0]