From 57fb47de3a41c724c3bf1051d00715e08d86141e Mon Sep 17 00:00:00 2001
From: Simon Cozens <simon@simon-cozens.org>
Date: Mon, 7 Aug 2023 17:12:12 +0100
Subject: [PATCH] Allow for merging of NULL anchors (#3248)

* A failing test for #3247

* Fix up NULL entry/exit records on merge, fixes #3247
---
 Lib/fontTools/varLib/merger.py | 9 +++++++++
 Tests/varLib/merger_test.py    | 6 ++++++
 2 files changed, 15 insertions(+)

diff --git a/Lib/fontTools/varLib/merger.py b/Lib/fontTools/varLib/merger.py
index a4db492b7..b2c34016b 100644
--- a/Lib/fontTools/varLib/merger.py
+++ b/Lib/fontTools/varLib/merger.py
@@ -936,6 +936,15 @@ def merge(merger, self, lst):
     self.EntryExitCount = len(self.EntryExitRecord)
 
 
+@AligningMerger.merger(ot.EntryExitRecord)
+def merge(merger, self, lst):
+    if all(master.EntryAnchor is None for master in lst):
+        self.EntryAnchor = None
+    if all(master.ExitAnchor is None for master in lst):
+        self.ExitAnchor = None
+    merger.mergeObjects(self, lst)
+
+
 @AligningMerger.merger(ot.Lookup)
 def merge(merger, self, lst):
     subtables = merger.lookup_subtables = [l.SubTable for l in lst]
diff --git a/Tests/varLib/merger_test.py b/Tests/varLib/merger_test.py
index e5ae61c60..e44d466da 100644
--- a/Tests/varLib/merger_test.py
+++ b/Tests/varLib/merger_test.py
@@ -1902,32 +1902,38 @@ class SparsePositioningMergerTest:
 
         ds.sources[0].font.newGlyph("a").unicode = ord("a")
         ds.sources[0].font.newGlyph("b").unicode = ord("b")
+        ds.sources[0].font.newGlyph("c").unicode = ord("c")
         ds.sources[
             0
         ].font.features.text = """
         feature curs {
           position cursive a <anchor 400 20> <anchor 0 -20>;
+          position cursive c <anchor NULL> <anchor 0 -20>;
         } curs;
         """
 
         ds.sources[1].font.newGlyph("a").unicode = ord("a")
         ds.sources[1].font.newGlyph("b").unicode = ord("b")
+        ds.sources[1].font.newGlyph("c").unicode = ord("c")
         ds.sources[
             1
         ].font.features.text = """
         feature curs {
           position cursive a <anchor 500 20> <anchor 0 -20>;
           position cursive b <anchor 50 22> <anchor 0 -10>;
+          position cursive c <anchor NULL> <anchor 0 -20>;
         } curs;
         """
 
         ds.sources[2].font.newGlyph("a").unicode = ord("a")
         ds.sources[2].font.newGlyph("b").unicode = ord("b")
+        ds.sources[2].font.newGlyph("c").unicode = ord("c")
         ds.sources[
             2
         ].font.features.text = """
         feature curs {
           position cursive b <anchor 100 40> <anchor 0 -30>;
+          position cursive c <anchor NULL> <anchor 0 -20>;
         } curs;
         """