Merge pull request #1706 from dscorbett/splitMultipleSubst

Fix MultipleSubst subtable overflows

Lib/fontTools/ttLib/tables/otTables.py

@@ -1226,6 +1226,32 @@ def fixLookupOverFlows(ttf, overflowRecord):
 	ok = 1
 	return ok
 
+def splitMultipleSubst(oldSubTable, newSubTable, overflowRecord):
+	ok = 1
+	newSubTable.Format = oldSubTable.Format
+	oldMapping = sorted(oldSubTable.mapping.items())
+	oldLen = len(oldMapping)
+
+	if overflowRecord.itemName in ['Coverage', 'RangeRecord']:
+		# Coverage table is written last. Overflow is to or within the
+		# the coverage table. We will just cut the subtable in half.
+		newLen = oldLen // 2
+
+	elif overflowRecord.itemName == 'Sequence':
+		# We just need to back up by two items from the overflowed
+		# Sequence index to make sure the offset to the Coverage table
+		# doesn't overflow.
+		newLen = overflowRecord.itemIndex - 1
+
+	newSubTable.mapping = {}
+	for i in range(newLen, oldLen):
+		item = oldMapping[i]
+		key = item[0]
+		newSubTable.mapping[key] = item[1]
+		del oldSubTable.mapping[key]
+
+	return ok
+
 def splitAlternateSubst(oldSubTable, newSubTable, overflowRecord):
 	ok = 1
 	newSubTable.Format = oldSubTable.Format
@@ -1413,7 +1439,7 @@ def splitMarkBasePos(oldSubTable, newSubTable, overflowRecord):
 
 splitTable = {	'GSUB': {
 #					1: splitSingleSubst,
-#					2: splitMultipleSubst,
+					2: splitMultipleSubst,
 					3: splitAlternateSubst,
 					4: splitLigatureSubst,
 #					5: splitContextSubst,

Tests/ttLib/tables/otTables_test.py

@@ -546,6 +546,37 @@ class InsertionMorphActionTest(unittest.TestCase):
         })
 
 
+class SplitMultipleSubstTest:
+    def overflow(self, itemName, itemRecord):
+        from fontTools.otlLib.builder import buildMultipleSubstSubtable
+        from fontTools.ttLib.tables.otBase import OverflowErrorRecord
+
+        oldSubTable = buildMultipleSubstSubtable({'e': 1, 'a': 2, 'b': 3, 'c': 4, 'd': 5})
+        oldSubTable.Format = 1
+        newSubTable = otTables.MultipleSubst()
+
+        ok = otTables.splitMultipleSubst(oldSubTable, newSubTable, OverflowErrorRecord((None, None, None, itemName, itemRecord)))
+
+        assert ok
+        assert oldSubTable.Format == newSubTable.Format
+        return oldSubTable.mapping, newSubTable.mapping
+
+    def test_Coverage(self):
+        oldMapping, newMapping = self.overflow('Coverage', None)
+        assert oldMapping == {'a': 2, 'b': 3}
+        assert newMapping == {'c': 4, 'd': 5, 'e': 1}
+
+    def test_RangeRecord(self):
+        oldMapping, newMapping = self.overflow('RangeRecord', None)
+        assert oldMapping == {'a': 2, 'b': 3}
+        assert newMapping == {'c': 4, 'd': 5, 'e': 1}
+
+    def test_Sequence(self):
+        oldMapping, newMapping = self.overflow('Sequence', 4)
+        assert oldMapping == {'a': 2, 'b': 3,'c': 4}
+        assert newMapping == {'d': 5, 'e': 1}
+
+
 def test_splitMarkBasePos():
 	from fontTools.otlLib.builder import buildAnchor, buildMarkBasePosSubtable