[AAT] Do not prune AATLookup values

Before this change, the decoder would silently remove "redundant" values
when decompiling AAT lookups. However, it is perfectly valid for a lookup
to map a glyph ID to itself, and also not all AAT lookups have glyph IDs as
their value range.

Lib/fontTools/ttLib/tables/otConverters.py

@@ -565,18 +565,16 @@ class AATLookup(BaseConverter):
 	def read(self, reader, font, tableDict):
 		format = reader.readUShort()
 		conv = self.tableClass(name='Value', repeat=None, aux=None)
-		# TODO: Do not prune the results.
-		prune = lambda x: {k:v for k,v in x.items() if k != v}
 		if format == 0:
-			return prune(self.readFormat0(reader, font, conv))
+			return self.readFormat0(reader, font, conv)
 		elif format == 2:
-			return prune(self.readFormat2(reader, font, conv))
+			return self.readFormat2(reader, font, conv)
 		elif format == 4:
-			return prune(self.readFormat4(reader, font, conv))
+			return self.readFormat4(reader, font, conv)
 		elif format == 6:
-			return prune(self.readFormat6(reader, font, conv))
+			return self.readFormat6(reader, font, conv)
 		elif format == 8:
-			return prune(self.readFormat8(reader, font, conv))
+			return self.readFormat8(reader, font, conv)
 		else:
 			assert False, "unsupported lookup format: %d" % format
 

Tests/ttLib/tables/otConverters_test.py

@@ -189,6 +189,9 @@ class AATLookupTest(unittest.TestCase):
     def test_readFormat0(self):
         reader = OTTableReader(deHexStr("0000 0000 0001 0002 0000 7D00 0001"))
         self.assertEqual(self.converter.read(reader, self.font, None), {
+            ".notdef": ".notdef",
+            "A": "A",
+            "B": "B",
             "C": ".notdef",
             "D": "glyph32000",
             "E": "A"