writeLayerContents: make sure bytes strings in layerOrder are decoded

looks like defcon LayerSet.newLayer does not ensure the 'name' argument is a unicode
string, so serializing the layercontents.plist with the new ufoLib.plistlib may
lead to the layer name being encoded as a <data> element instead of a <string>.

Thanks Miguel for noticing this.

Author: anthrotype

Lib/ufoLib/__init__.py

@@ -3,7 +3,7 @@
 import shutil
 from io import StringIO, BytesIO, open
 from copy import deepcopy
-from fontTools.misc.py23 import basestring, unicode
+from fontTools.misc.py23 import basestring, unicode, tounicode
 from ufoLib.glifLib import GlyphSet
 from ufoLib.validators import *
 from ufoLib.filenames import userNameToFileName
@@ -1109,6 +1109,8 @@ def writeLayerContents(self, layerOrder=None, validate=None):
 			for layerName in layerOrder:
 				if layerName is None:
 					layerName = DEFAULT_LAYER_NAME
+				else:
+					layerName = tounicode(layerName)
 				newOrder.append(layerName)
 			layerOrder = newOrder
 		else:

Lib/ufoLib/test/test_UFO3.py

@@ -5,6 +5,7 @@
 import unittest
 import tempfile
 from io import open
+from fontTools.misc.py23 import unicode
 from ufoLib import UFOReader, UFOWriter, UFOLibError
 from ufoLib.glifLib import GlifLibError
 from ufoLib import plistlib
@@ -4130,6 +4131,28 @@ def testRemoveDefaultLayer(self):
 		writer = UFOWriter(self.ufoPath)
 		self.assertRaises(UFOLibError, writer.deleteGlyphSet, "does not exist")
 
+	def testWriteAsciiLayerOrder(self):
+		self.makeUFO(
+			layerContents=[
+				["public.default", "glyphs"],
+				["layer 1", "glyphs.layer 1"],
+				["layer 2", "glyphs.layer 2"],
+			]
+		)
+		writer = UFOWriter(self.ufoPath)
+		# if passed bytes string, it'll be decoded to ASCII unicode string
+		writer.writeLayerContents(["public.default", "layer 2", b"layer 1"])
+		path = os.path.join(self.ufoPath, "layercontents.plist")
+		with open(path, "rb") as f:
+			result = plistlib.load(f)
+		expected = [
+			["public.default", "glyphs"],
+			["layer 2", "glyphs.layer 2"],
+			["layer 1", "glyphs.layer 1"],
+		]
+		self.assertEqual(expected, result)
+		for layerName, directory in result:
+			assert isinstance(layerName, unicode)
 
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