[subset] fox for (Chain)ContextFormat3: subset lookupRecord

skip copying a lookupRecord if lookup referenced in the lookupRecord is
not retained after subset

src/hb-ot-layout-gsubgpos.hh

@@ -1618,7 +1618,14 @@ struct Rule
     const UnsizedArrayOf<LookupRecord> &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
 						       (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));
     for (unsigned i = 0; i < (unsigned) lookupCount; i++)
+    {
+      if (!lookup_map->has (lookupRecord[i].lookupListIndex))
+      {
+        out->lookupCount--;
+        continue;
+      }
       c->copy (lookupRecord[i], lookup_map);
+    }
 
     return_trace (true);
   }
@@ -2234,7 +2241,14 @@ struct ContextFormat3
     const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
     const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
     for (unsigned i = 0; i < (unsigned) lookupCount; i++)
+    {
+      if (!lookup_map->has (lookupRecord[i].lookupListIndex))
+      {
+        out->lookupCount--;
+        continue;
+      }
       c->serializer->copy (lookupRecord[i], lookup_map);
+    }
 
     return_trace (true);
   }
@@ -3303,13 +3317,21 @@ struct ChainContextFormat3
       return_trace (false);
 
     const Array16Of<LookupRecord> &lookupRecord = StructAfter<Array16Of<LookupRecord>> (lookahead);
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+    hb_set_t lookup_indices;
+    for (unsigned i = 0; i < (unsigned) lookupRecord.len; i++)
+      if (lookup_map->has (lookupRecord[i].lookupListIndex))
+        lookup_indices.add (i);
+
     HBUINT16 lookupCount;
-    lookupCount = lookupRecord.len;
+    lookupCount = lookup_indices.get_population ();
     if (!c->serializer->copy (lookupCount)) return_trace (false);
 
-    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
-    for (unsigned i = 0; i < (unsigned) lookupCount; i++)
-      if (!c->serializer->copy (lookupRecord[i], lookup_map)) return_trace (false);
+    for (unsigned i : lookup_indices.iter ())
+    {
+      if (!c->serializer->copy (lookupRecord[i], lookup_map))
+        return_trace (false);
+    }
 
     return_trace (true);
   }

test/subset/data/Makefile.am

@@ -34,6 +34,7 @@ EXTRA_DIST += \
 	expected/layout.gdef-varstore \
 	expected/layout.gdef-attachlist \
 	expected/layout.notonastaliqurdu \
+	expected/layout.tinos \
 	expected/cmap \
 	expected/cmap14 \
 	expected/sbix \

test/subset/data/Makefile.sources

@@ -31,6 +31,7 @@ TESTS = \
 	tests/layout.khmer.tests \
 	tests/layout.notonastaliqurdu.tests \
 	tests/layout.tests \
+	tests/layout.tinos.tests \
 	tests/sbix.tests \
 	tests/variable.tests \
 	tests/glyph_names.tests \

test/subset/data/tests/layout.tinos.tests

@@ -0,0 +1,12 @@
+FONTS:
+Tinos-Italic.ttf
+
+PROFILES:
+default.txt
+retain-gids.txt
+glyph-names.txt
+notdef-outline.txt
+
+SUBSETS:
+U+5bf,U+5f0,U+5f1,U+5f2,U+fb21,U+fb22,U+fb23,U+fb24,U+fb25,U+fb26,U+fb27,U+fb28
+*

test/subset/meson.build

@@ -26,6 +26,7 @@ tests = [
   'layout.gdef-varstore',
   'layout.gdef-attachlist',
   'layout.notonastaliqurdu',
+  'layout.tinos',
   'cmap',
   'cmap14',
   'sbix',