From 2d3610bb6b191a8a9fda9bc4621c2bd27c44468d Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 26 Dec 2016 17:26:14 -0500
Subject: [PATCH] Ignore class=0 when reading & writing ClassDef objects

class=0 items might be added as an optimization.  They have no semantic value.
Ignore them.

Fixes the last of mtiLib tests.
---
 .../mtiLib/testdata/mti/gposkernset.ttx.GPOS       |  2 --
 Lib/fontTools/ttLib/tables/otTables.py             | 14 ++++++++------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/Lib/fontTools/mtiLib/testdata/mti/gposkernset.ttx.GPOS b/Lib/fontTools/mtiLib/testdata/mti/gposkernset.ttx.GPOS
index 1f7db54fe..850129f4c 100644
--- a/Lib/fontTools/mtiLib/testdata/mti/gposkernset.ttx.GPOS
+++ b/Lib/fontTools/mtiLib/testdata/mti/gposkernset.ttx.GPOS
@@ -54,8 +54,6 @@
           <ClassDef glyph="Ocircumflex" class="2"/>
           <ClassDef glyph="Ograve" class="2"/>
           <ClassDef glyph="T" class="3"/>
-          <ClassDef glyph="V" class="0"/>
-          <ClassDef glyph="acircumflex" class="0"/>
         </ClassDef1>
         <ClassDef2 Format="2">
           <ClassDef glyph="V" class="1"/>
diff --git a/Lib/fontTools/ttLib/tables/otTables.py b/Lib/fontTools/ttLib/tables/otTables.py
index 9e7b3c002..3016db989 100644
--- a/Lib/fontTools/ttLib/tables/otTables.py
+++ b/Lib/fontTools/ttLib/tables/otTables.py
@@ -389,7 +389,8 @@ class ClassDef(FormatSwitchingBaseTable):
 				endID = len(glyphOrder)
 
 			for glyphID, cls in zip(range(startID, endID), classList):
-				classDefs[glyphOrder[glyphID]] = cls
+				if cls:
+					classDefs[glyphOrder[glyphID]] = cls
 
 		elif self.Format == 2:
 			records = rawTable["ClassRangeRecord"]
@@ -412,7 +413,8 @@ class ClassDef(FormatSwitchingBaseTable):
 					# but none that we have seen in the wild.
 					endID = len(glyphOrder)
 				for glyphID in range(startID, endID):
-					classDefs[glyphOrder[glyphID]] = cls
+					if cls:
+						classDefs[glyphOrder[glyphID]] = cls
 		else:
 			assert 0, "unknown format: %s" % self.Format
 		self.classDefs = classDefs
@@ -421,13 +423,13 @@ class ClassDef(FormatSwitchingBaseTable):
 		classDefs = getattr(self, "classDefs", None)
 		if classDefs is None:
 			classDefs = self.classDefs = {}
-		items = list(classDefs.items())
 		format = 2
 		rawTable = {"ClassRangeRecord": []}
 		getGlyphID = font.getGlyphID
-		for i in range(len(items)):
-			glyphName, cls = items[i]
-			items[i] = getGlyphID(glyphName), glyphName, cls
+		items = []
+		for glyphName, cls in classDefs.items():
+			if not cls: continue
+			items.append((getGlyphID(glyphName), glyphName, cls))
 		items.sort()
 		if items:
 			last, lastName, lastCls = items[0]