From 2dcdb17e9096247be58a1a41bae7d0d8a8c9634a Mon Sep 17 00:00:00 2001
From: Cosimo Lupo <clupo@google.com>
Date: Thu, 20 Jul 2023 11:15:03 +0100
Subject: [PATCH] instancer_test: add test for null ConditionSet offset

---
 Tests/varLib/instancer/instancer_test.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Tests/varLib/instancer/instancer_test.py b/Tests/varLib/instancer/instancer_test.py
index 7ee0a6a14..0b0702d7a 100644
--- a/Tests/varLib/instancer/instancer_test.py
+++ b/Tests/varLib/instancer/instancer_test.py
@@ -1822,6 +1822,24 @@ class InstantiateFeatureVariationsTest(object):
         else:
             assert not gsub.FeatureList.FeatureRecord
 
+    def test_null_conditionset(self):
+        # A null ConditionSet offset should be treated like an empty ConditionTable, i.e.
+        # all contexts are matched; see https://github.com/fonttools/fonttools/issues/3211
+        font = makeFeatureVarsFont(
+            [([{"wght": (-1.0, 1.0)}], {"uni0024": "uni0024.nostroke"})]
+        )
+        gsub = font["GSUB"].table
+        gsub.FeatureVariations.FeatureVariationRecord[0].ConditionSet = None
+
+        location = instancer.NormalizedAxisLimits({"wght": 0.5})
+        instancer.instantiateFeatureVariations(font, location)
+
+        assert not hasattr(gsub, "FeatureVariations")
+        assert gsub.Version == 0x00010000
+
+        lookupIndices = gsub.FeatureList.FeatureRecord[0].Feature.LookupListIndex
+        assert _getSubstitutions(gsub, lookupIndices) == {"uni0024": "uni0024.nostroke"}
+
     def test_unsupported_condition_format(self, caplog):
         font = makeFeatureVarsFont(
             [