From 890c5061b5058c5de08b12a5bf54c161bac3d25e Mon Sep 17 00:00:00 2001
From: Cosimo Lupo <clupo@google.com>
Date: Mon, 11 May 2020 13:32:18 +0100
Subject: [PATCH] subset: fix issue subsetting Context{Subst,Pos}Format3

Fixes https://github.com/fonttools/fonttools/issues/1879

In ChainContext{Subst,Pos}Format3, the array of input coverages is called
InputCoverage, whereas in non-Chain Context{Subst,Pos}Format3 subtables it
is called simply Coverage.
---
 Lib/fontTools/subset/__init__.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Lib/fontTools/subset/__init__.py b/Lib/fontTools/subset/__init__.py
index 0119a92bd..701c1aa25 100644
--- a/Lib/fontTools/subset/__init__.py
+++ b/Lib/fontTools/subset/__init__.py
@@ -894,6 +894,8 @@ def __subset_classify_context(self):
 				self.ClassDef = 'InputClassDef' if Chain else 'ClassDef'
 				self.ClassDefIndex = 1 if Chain else 0
 				self.Input = 'Input' if Chain else 'Class'
+			elif Format == 3:
+				self.Input = 'InputCoverage' if Chain else 'Coverage'
 
 	if self.Format not in [1, 2, 3]:
 		return None	# Don't shoot the messenger; let it go
@@ -976,6 +978,7 @@ def closure_glyphs(self, s, cur_glyphs):
 		if not all(x.intersect(s.glyphs) for x in c.RuleData(self)):
 			return []
 		r = self
+		input_coverages = getattr(r, c.Input)
 		chaos = set()
 		for ll in getattr(r, c.LookupRecord):
 			if not ll: continue
@@ -987,11 +990,11 @@ def closure_glyphs(self, s, cur_glyphs):
 				if seqi == 0:
 					pos_glyphs = frozenset(cur_glyphs)
 				else:
-					pos_glyphs = frozenset(r.InputCoverage[seqi].intersect_glyphs(s.glyphs))
+					pos_glyphs = frozenset(input_coverages[seqi].intersect_glyphs(s.glyphs))
 			lookup = s.table.LookupList.Lookup[ll.LookupListIndex]
 			chaos.add(seqi)
 			if lookup.may_have_non_1to1():
-				chaos.update(range(seqi, len(r.InputCoverage)+1))
+				chaos.update(range(seqi, len(input_coverages)+1))
 			lookup.closure_glyphs(s, cur_glyphs=pos_glyphs)
 	else:
 		assert 0, "unknown format: %s" % self.Format