From 8b69b9412e6ccf3aad4fa488470a0c2a18d0176f Mon Sep 17 00:00:00 2001
From: David Corbett <corbett.dav@northeastern.edu>
Date: Sat, 13 May 2023 13:24:58 -0400
Subject: [PATCH] feaLib: Dedupe multiple substitutions with classes

---
 Lib/fontTools/feaLib/ast.py | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/Lib/fontTools/feaLib/ast.py b/Lib/fontTools/feaLib/ast.py
index bbe6e6e74..17c6cc3fb 100644
--- a/Lib/fontTools/feaLib/ast.py
+++ b/Lib/fontTools/feaLib/ast.py
@@ -1272,15 +1272,18 @@ class MultipleSubstStatement(Statement):
             replaces.append(replace)
         replaces = list(zip(*replaces))
 
+        seen_originals = set()
         for i, original in enumerate(originals):
-            builder.add_multiple_subst(
-                self.location,
-                prefix,
-                original,
-                suffix,
-                replaces and replaces[i] or (),
-                self.forceChain,
-            )
+            if original not in seen_originals:
+                seen_originals.add(original)
+                builder.add_multiple_subst(
+                    self.location,
+                    prefix,
+                    original,
+                    suffix,
+                    replaces and replaces[i] or (),
+                    self.forceChain,
+                )
 
     def asFea(self, indent=""):
         res = "sub "