[cffLib] Make sure glyph names are unique

Similar to what we do with “post” table names. I’d have said the font is
broken, but all applications I tried it with loaded it just fine, though
they differed in which glyph to pick from the duplicate ones.

Fixes https://github.com/fonttools/fonttools/issues/1602

Lib/fontTools/cffLib/__init__.py

@@ -1319,6 +1319,20 @@ class CharsetConverter(SimpleConverter):
 				raise NotImplementedError
 			assert len(charset) == numGlyphs
 			log.log(DEBUG, "    charset end at %s", file.tell())
+			# make sure glyph names are unique
+			allNames = {}
+			newCharset = []
+			for glyphName in charset:
+				if glyphName in allNames:
+					# make up a new glyphName that's unique
+					n = allNames[glyphName]
+					while (glyphName + "#" + str(n)) in allNames:
+						n += 1
+					allNames[glyphName] = n + 1
+					glyphName = glyphName + "#" + str(n)
+				allNames[glyphName] = 1
+				newCharset.append(glyphName)
+			charset = newCharset
 		else:  # offset == 0 -> no charset data.
 			if isCID or "CharStrings" not in parent.rawDict:
 				# We get here only when processing fontDicts from the FDArray of

Tests/cffLib/cffLib_test.py

@@ -92,6 +92,21 @@ class CffLibTest(DataFilesHandler):
         self.assertEqual(topDict2.FDSelect.format, 4)
         self.assertEqual(topDict2.FDSelect.gidArray, [0, 0, 1])
 
+    def test_unique_glyph_names(self):
+        font_path = self.getpath('LinLibertine_RBI.otf')
+        font = TTFont(font_path, recalcBBoxes=False, recalcTimestamp=False)
+
+        glyphOrder = font.getGlyphOrder()
+        self.assertEqual(len(glyphOrder), len(set(glyphOrder)))
+
+        self.temp_dir()
+        save_path = os.path.join(self.tempdir, 'TestOTF.otf')
+        font.save(save_path)
+
+        font2 = TTFont(save_path)
+        glyphOrder = font2.getGlyphOrder()
+        self.assertEqual(len(glyphOrder), len(set(glyphOrder)))
+
 
 if __name__ == "__main__":
     sys.exit(unittest.main())