Regression: After a7bd6d7a4c53ff61 hb_ot_layout_lookup_collect_glyphs fails to collect glyphs when params before, input, after are NULL

[drott]

See also https://bugs.chromium.org/p/chromium/issues/detail?id=796124

Patching afshaper as follows:

diff --git a/src/autofit/afshaper.c b/src/autofit/afshaper.c
index 8ee9ba1a..4e03c7bc 100644
--- a/src/autofit/afshaper.c
+++ b/src/autofit/afshaper.c
@@ -108,6 +108,9 @@
     hb_set_t*  gsub_glyphs  = NULL; /* glyphs covered by GSUB lookups  */
     hb_set_t*  gpos_lookups = NULL; /* GPOS lookups for a given script */
     hb_set_t*  gpos_glyphs  = NULL; /* glyphs covered by GPOS lookups  */
+    hb_set_t* dummy_glyphs_1 = NULL;
+    hb_set_t* dummy_glyphs_2 = NULL;
+    hb_set_t* dummy_glyphs_3 = NULL;
 
     hb_script_t      script;
     const hb_tag_t*  coverage_tags;
@@ -183,6 +186,9 @@
 #endif
 
     gsub_glyphs = hb_set_create();
+    dummy_glyphs_1 = hb_set_create();
+    dummy_glyphs_2 = hb_set_create();
+    dummy_glyphs_3 = hb_set_create();
     for ( idx = HB_SET_VALUE_INVALID; hb_set_next( gsub_lookups, &idx ); )
     {
 #ifdef FT_DEBUG_LEVEL_TRACE
@@ -191,12 +197,19 @@
 #endif
 
       /* get output coverage of GSUB feature */
+      /* hb_ot_layout_lookup_collect_glyphs( face, */
+      /*                                     HB_OT_TAG_GSUB, */
+      /*                                     idx, */
+      /*                                     NULL, */
+      /*                                     NULL, */
+      /*                                     NULL, */
+      /*                                     gsub_glyphs ); */
       hb_ot_layout_lookup_collect_glyphs( face,
                                           HB_OT_TAG_GSUB,
                                           idx,
-                                          NULL,
-                                          NULL,
-                                          NULL,
+                                          dummy_glyphs_1,
+                                          dummy_glyphs_2,
+                                          dummy_glyphs_3,
                                           gsub_glyphs );
     }
 

produces a glyph with autohinting, while without this patch, it doesn't. This is after HarfBuzz commit a7bd6d7.

This breaks a Noto Devanagari layout test on Chrome as the new result does not have autohinting.

[drott]

https://gist.github.com/drott/c78215e20bf23648f11a05ff3850a13c was used for testing, building against libfreetype_harfbuzz.so as part of the Chromium checkout.

[behdad]

Thanks. Let me check.

[drott]

Thanks very much, locally verified fixed. Roll CL up in https://chromium-review.googlesource.com/c/chromium/src/+/831946

[drott]

Yep, landed the roll in https://chromium-review.googlesource.com/c/chromium/src/+/831946

[behdad]

Great. Thanks. Released 1.7.4 as well.