From 4ad6b0db134e75dbf9845ea6c9577b0beb3d5ef8 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 27 May 2024 16:22:19 -0600
Subject: [PATCH] [CFF2ToCFF] Map charset to CIDs

This seems to fix the case of ttx not handling the results.
I *think* this fixes the rest of the issues I've been seeing
with this conversion.
---
 Lib/fontTools/cffLib/CFF2ToCFF.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Lib/fontTools/cffLib/CFF2ToCFF.py b/Lib/fontTools/cffLib/CFF2ToCFF.py
index 6002069a2..f929cc968 100644
--- a/Lib/fontTools/cffLib/CFF2ToCFF.py
+++ b/Lib/fontTools/cffLib/CFF2ToCFF.py
@@ -100,6 +100,21 @@ def _convertCFF2ToCFF(cff, otFont):
         if width != private.defaultWidthX:
             cs.program.insert(0, width - private.nominalWidthX)
 
+    mapping = {
+        name: ("cid" + str(n) if n else ".notdef")
+        for n, name in enumerate(topDict.charset)
+    }
+    topDict.charset = [
+        "cid" + str(n) if n else ".notdef" for n in range(len(topDict.charset))
+    ]
+    charStrings.charStrings = {
+        mapping[name]: v for name, v in charStrings.charStrings.items()
+    }
+
+    # I'm not sure why the following is *not* necessary. And it breaks
+    # the output if I add it.
+    # topDict.ROS = ("Adobe", "Identity", 0)
+
 
 def convertCFF2ToCFF(font, *, updatePostTable=True):
     cff = font["CFF2"].cff