gh-152847: Reject non-digit day-of-year in pure-Python zoneinfo POSIX TZ rules

The J and n day-of-year branches of _parse_dst_start_end() fell through to a
bare int(date), accepting input the C accelerator rejects (for example J1_0,
which int() reads as day 10, silently building a different zone). Guard the
branch with an re.ASCII digit match mirroring the C parser's
parse_digits(1, 3), so both implementations agree.

Author: tonghuaroot

Lib/test/test_zoneinfo/test_zoneinfo.py

@@ -1111,6 +1111,9 @@ def test_extreme_tzstr(self):
             "AAA4BBB,J1/2,J1/14",
             "AAA4BBB,J20/2,J365/2",
             "AAA4BBB,J365/2,J365/14",
+            # Leading-zero day-of-year
+            "AAA4BBB,J001/2,J065/2",
+            "AAA4BBB,001/2,065/2",
             # Extreme transition hour
             "AAA4BBB,J60/167,J300/2",
             "AAA4BBB,J60/+167,J300/2",
@@ -1209,6 +1212,15 @@ def test_invalid_tzstr(self):
             # Invalid julian offset
             "AAA4BBB,J0/2,J20/2",
             "AAA4BBB,J20/2,J366/2",
+            # gh-152847: non-digit day-of-year (e.g. J1_0)
+            "AAA4BBB,J1_0,J300/2",
+            "AAA4BBB,J60/2,J30_0/2",
+            "AAA4BBB,1_0,J300/2",
+            "AAA4BBB,J+1,J300/2",
+            "AAA4BBB,J 1,J300/2",
+            "AAA4BBB, 1,J300/2",
+            "AAA4BBB,J0001,J300/2",
+            "AAA4BBB,0001,J300/2",
             # Invalid transition time
             "AAA4BBB,J60/2/3,J300/2",
             "AAA4BBB,J60/2,J300/2/3",
@@ -1248,6 +1260,15 @@ def test_invalid_tzstr_non_ascii_abbr(self):
         with self.assertRaisesRegex(ValueError, expected):
             self.zone_from_tzstr(tzstr, encoding="utf-8")
 
+    def test_invalid_tzstr_non_ascii_dst_date(self):
+        tzstr = "AAA4BBB,J١,J300/2"
+        if self.module is py_zoneinfo:
+            expected = re.escape(tzstr)
+        else:
+            expected = re.escape(repr(tzstr.encode("utf-8")))
+        with self.assertRaisesRegex(ValueError, expected):
+            self.zone_from_tzstr(tzstr, encoding="utf-8")
+
     @classmethod
     def _populate_test_cases(cls):
         # This method uses a somewhat unusual style in that it populates the

Lib/zoneinfo/_zoneinfo.py

@@ -720,6 +720,8 @@ def _parse_dst_start_end(dststr):
         else:
             n_is_julian = False
 
+        if re.fullmatch(r"\d{1,3}", date, re.ASCII) is None:
+            raise ValueError(f"Invalid dst start/end date: {dststr}")
         doy = int(date)
         offset = _DayOffset(doy, n_is_julian)
 

Misc/NEWS.d/next/Library/2026-07-02-12-00-00.gh-issue-152847.PitKqc.rst

@@ -0,0 +1,3 @@
+Fix the pure-Python :mod:`zoneinfo` parser accepting non-digit characters in
+the day-of-year field of a POSIX TZ transition rule (such as ``J1_0``), which
+the C implementation rejects. Patch by tonghuaroot.