From 8697f91cdc3f8e5fed67cdee3b45635b662711ac Mon Sep 17 00:00:00 2001
From: Cosimo Lupo <clupo@google.com>
Date: Fri, 11 Nov 2022 12:20:37 +0000
Subject: [PATCH] [unicodedata] map Zmth<->math in ot_tag_{to,from}_script

Fixes https://github.com/fonttools/fonttools/issues/1737
---
 Lib/fontTools/unicodedata/OTTags.py   |  5 +++++
 Lib/fontTools/unicodedata/__init__.py | 13 +++++++------
 Tests/unicodedata_test.py             |  2 ++
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/Lib/fontTools/unicodedata/OTTags.py b/Lib/fontTools/unicodedata/OTTags.py
index a9d8cd1ce..859a3bcdc 100644
--- a/Lib/fontTools/unicodedata/OTTags.py
+++ b/Lib/fontTools/unicodedata/OTTags.py
@@ -22,11 +22,16 @@ SCRIPT_EXCEPTIONS = {
     "Yiii": "yi  ",
     "Nkoo": "nko ",
     "Vaii": "vai ",
+    "Zmth": "math",
     "Zinh": DEFAULT_SCRIPT,
     "Zyyy": DEFAULT_SCRIPT,
     "Zzzz": DEFAULT_SCRIPT,
 }
 
+SCRIPT_EXCEPTIONS_REVERSED = {
+    "math": "Zmth",
+}
+
 NEW_SCRIPT_TAGS = {
     "Beng": ("bng2",),
     "Deva": ("dev2",),
diff --git a/Lib/fontTools/unicodedata/__init__.py b/Lib/fontTools/unicodedata/__init__.py
index 4546ef3f0..29f7252b6 100644
--- a/Lib/fontTools/unicodedata/__init__.py
+++ b/Lib/fontTools/unicodedata/__init__.py
@@ -239,15 +239,13 @@ def ot_tags_from_script(script_code):
     Unicode script code.
     Return ['DFLT'] script tag for invalid/unknown script codes.
     """
+    if script_code in OTTags.SCRIPT_EXCEPTIONS:
+        return [OTTags.SCRIPT_EXCEPTIONS[script_code]]
+
     if script_code not in Scripts.NAMES:
         return [OTTags.DEFAULT_SCRIPT]
 
-    script_tags = [
-        OTTags.SCRIPT_EXCEPTIONS.get(
-            script_code,
-            script_code[0].lower() + script_code[1:]
-        )
-    ]
+    script_tags = [script_code[0].lower() + script_code[1:]]
     if script_code in OTTags.NEW_SCRIPT_TAGS:
         script_tags.extend(OTTags.NEW_SCRIPT_TAGS[script_code])
         script_tags.reverse()  # last in, first out
@@ -278,6 +276,9 @@ def ot_tag_to_script(tag):
     if tag in OTTags.NEW_SCRIPT_TAGS_REVERSED:
         return OTTags.NEW_SCRIPT_TAGS_REVERSED[tag]
 
+    if tag in OTTags.SCRIPT_EXCEPTIONS_REVERSED:
+        return OTTags.SCRIPT_EXCEPTIONS_REVERSED[tag]
+
     # This side of the conversion is fully algorithmic
 
     # Any spaces at the end of the tag are replaced by repeating the last
diff --git a/Tests/unicodedata_test.py b/Tests/unicodedata_test.py
index 92995b4a1..bc950e550 100644
--- a/Tests/unicodedata_test.py
+++ b/Tests/unicodedata_test.py
@@ -210,6 +210,7 @@ def test_ot_tags_from_script():
     assert unicodedata.ot_tags_from_script("Deva") == ["dev2", "deva"]
     # exceptions
     assert unicodedata.ot_tags_from_script("Hira") == ["kana"]
+    assert unicodedata.ot_tags_from_script("Zmth") == ["math"]
     # special script codes map to DFLT
     assert unicodedata.ot_tags_from_script("Zinh") == ["DFLT"]
     assert unicodedata.ot_tags_from_script("Zyyy") == ["DFLT"]
@@ -232,6 +233,7 @@ def test_ot_tag_to_script():
     assert unicodedata.ot_tag_to_script("vai ") == "Vaii"
     assert unicodedata.ot_tag_to_script("lao ") == "Laoo"
     assert unicodedata.ot_tag_to_script("yi") == "Yiii"
+    assert unicodedata.ot_tag_to_script("math") == "Zmth"
     # both 'hang' and 'jamo' tags map to the Hangul script
     assert unicodedata.ot_tag_to_script("hang") == "Hang"
     assert unicodedata.ot_tag_to_script("jamo") == "Hang"