Add old-Myanmar shaper

Looks like Unsicribe responds to the 'mymr' tag by zeroing marks
GDEF_LATE instead of generic-shaper UNICODE_LATE.  Implement that.

Fixes
Bug 81775 - Incorrect Rendering with harfbuzz-ng myanmar unicode
https://bugs.freedesktop.org/show_bug.cgi?id=81775

Micro-test added based on Padauk.

7 files changed, 25 insertions, 2 deletions

diff --git a/src/hb-ot-shape-complex-myanmar.cc b/src/hb-ot-shape-complex-myanmar.cc
index 258ccc47..d016380c 100644
--- a/src/hb-ot-shape-complex-myanmar.cc
+++ b/src/hb-ot-shape-complex-myanmar.cc
@@ -536,6 +536,24 @@ final_reordering (const hb_ot_shape_plan_t *plan,
 }
 
 
+/* Uniscribe seems to have a shaper for 'mymr' that is like the
+ * generic shaper, except that it zeros mark advances GDEF_LATE. */
+const hb_ot_complex_shaper_t _hb_ot_complex_shaper_myanmar_old =
+{
+  "default",
+  NULL, /* collect_features */
+  NULL, /* override_features */
+  NULL, /* data_create */
+  NULL, /* data_destroy */
+  NULL, /* preprocess_text */
+  HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
+  NULL, /* decompose */
+  NULL, /* compose */
+  NULL, /* setup_masks */
+  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
+  true, /* fallback_position */
+};
+
 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_myanmar =
 {
   "myanmar",
diff --git a/src/hb-ot-shape-complex-private.hh b/src/hb-ot-shape-complex-private.hh
index 3e581afa..9a7afcbd 100644
--- a/src/hb-ot-shape-complex-private.hh
+++ b/src/hb-ot-shape-complex-private.hh
@@ -56,6 +56,7 @@ enum hb_ot_shape_zero_width_marks_type_t {
   HB_COMPLEX_SHAPER_IMPLEMENT (arabic) \
   HB_COMPLEX_SHAPER_IMPLEMENT (hangul) \
   HB_COMPLEX_SHAPER_IMPLEMENT (hebrew) \
+  HB_COMPLEX_SHAPER_IMPLEMENT (myanmar_old) \
   HB_COMPLEX_SHAPER_IMPLEMENT (indic) \
   HB_COMPLEX_SHAPER_IMPLEMENT (myanmar) \
   HB_COMPLEX_SHAPER_IMPLEMENT (sea) \
@@ -329,10 +330,10 @@ hb_ot_shape_complex_categorize (const hb_ot_shape_planner_t *planner)
 	return &_hb_ot_complex_shaper_default;
 
     case HB_SCRIPT_MYANMAR:
-      /* For Myanmar, we only want to use the Myanmar shaper if the "new" script
-       * tag is found.  For "old" script tag we want to use the default shaper. */
       if (planner->map.chosen_script[0] == HB_TAG ('m','y','m','2'))
 	return &_hb_ot_complex_shaper_myanmar;
+      else if (planner->map.chosen_script[0] == HB_TAG ('m','y','m','r'))
+	return &_hb_ot_complex_shaper_myanmar_old;
       else
 	return &_hb_ot_complex_shaper_default;
 
diff --git a/test/shaping/Makefile.am b/test/shaping/Makefile.am
index c2c4db69..f40f2fff 100644
--- a/test/shaping/Makefile.am
+++ b/test/shaping/Makefile.am
@@ -41,6 +41,7 @@ TESTS = \
 	tests/indic-old-spec.tests \
 	tests/indic-pref-blocking.tests \
 	tests/mongolian-variation-selector.tests \
+	tests/zero-width-marks.tests \
 	$(NULL)
 
 TEST_EXTENSIONS = \
diff --git a/test/shaping/fonts/sha1sum/MANIFEST b/test/shaping/fonts/sha1sum/MANIFEST
index 4aaa54d5..0e9da647 100644
--- a/test/shaping/fonts/sha1sum/MANIFEST
+++ b/test/shaping/fonts/sha1sum/MANIFEST
@@ -7,6 +7,7 @@
 8a9fea2a7384f2116e5b84a9b31f83be7850ce21.ttf
 a919b33197965846f21074b24e30250d67277bce.ttf
 bb29ce50df2bdba2d10726427c6b7609bf460e04.ttf
+bb9473d2403488714043bcfb946c9f78b86ad627.ttf
 d629e7fedc0b350222d7987345fe61613fa3929a.ttf
 e207635780b42f898d58654b65098763e340f5c7.ttf
 ef86fe710cfea877bbe0dbb6946a1f88d0661031.ttf
diff --git a/test/shaping/fonts/sha1sum/bb9473d2403488714043bcfb946c9f78b86ad627.ttf b/test/shaping/fonts/sha1sum/bb9473d2403488714043bcfb946c9f78b86ad627.ttf
new file mode 100644
index 00000000..b16dae6c
--- /dev/null
+++ b/test/shaping/fonts/sha1sum/bb9473d2403488714043bcfb946c9f78b86ad627.ttf
diff --git a/test/shaping/tests/MANIFEST b/test/shaping/tests/MANIFEST
index a792e91b..8c2bdca1 100644
--- a/test/shaping/tests/MANIFEST
+++ b/test/shaping/tests/MANIFEST
@@ -3,3 +3,4 @@ context-matching.tests
 indic-old-spec.tests
 indic-pref-blocking.tests
 mongolian-variation-selector.tests
+zero-width-marks.tests
diff --git a/test/shaping/tests/zero-width-marks.tests b/test/shaping/tests/zero-width-marks.tests
new file mode 100644
index 00000000..bfe08093
--- /dev/null
+++ b/test/shaping/tests/zero-width-marks.tests
@@ -0,0 +1 @@
+fonts/sha1sum/bb9473d2403488714043bcfb946c9f78b86ad627.ttf:U+1030:[circledash=0+636|u1030.med=0@-162,0+0]