linkcheck: Use correct function to convert from UTC time to UNIX epoch

CHANGES

@@ -6,6 +6,7 @@ Bugs fixed
 
 * #11618: Fix a regression in the MoveModuleTargets transform,
   introduced in #10478 (#9662).
+* #11649: Use :py:func:`calendar.timegm` to convert from UTC time to UNIX epoch.
 
 Release 7.2.3 (released Aug 23, 2023)
 =====================================
@@ -24,7 +25,7 @@ Bugs fixed
   when ``autodoc_preserve_defaults`` is ``True``.
 * Restore support string methods on path objects.
   This is deprecated and will be removed in Sphinx 8.
-  Use :py:func`os.fspath` to convert :py:class:`~pathlib.Path` objects to strings,
+  Use :py:func:`os.fspath` to convert :py:class:`~pathlib.Path` objects to strings,
   or :py:class:`~pathlib.Path`'s methods to work with path objects.
 
 Release 7.2.2 (released Aug 17, 2023)

sphinx/builders/linkcheck.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import calendar
 import contextlib
 import json
 import re
@@ -491,7 +492,7 @@ def limit_rate(self, response_url: str, retry_after: str) -> float | None:
                     parsed = parsedate_tz(retry_after)
                     assert parsed is not None
                     # the 10th element is the GMT offset in seconds
-                    next_check = time.mktime(parsed[:9]) - (parsed[9] or 0)
+                    next_check = float(calendar.timegm(parsed[:9])) - (parsed[9] or 0)
                 except (AssertionError, TypeError, ValueError):
                     # TypeError: Invalid date format.
                     # ValueError: Invalid date, e.g. Oct 52th.

tests/test_build_linkcheck.py

@@ -4,6 +4,7 @@
 
 import http.server
 import json
+import os
 import re
 import textwrap
 import time
@@ -772,11 +773,22 @@ def test_too_many_requests_retry_after_int_delay(app, capsys, status):
     )
 
 
+@pytest.mark.parametrize('tz', ['GMT', 'GMT+3', 'GMT-3'])
 @pytest.mark.sphinx('linkcheck', testroot='linkcheck-localserver', freshenv=True)
-def test_too_many_requests_retry_after_HTTP_date(app, capsys):
-    retry_after = wsgiref.handlers.format_date_time(time.time())
-    with http_server(make_retry_after_handler([(429, retry_after), (200, None)])):
-        app.build()
+def test_too_many_requests_retry_after_HTTP_date(app, capsys, tz):
+    old_tz = os.environ.get('TZ')
+    os.environ['TZ'] = tz
+    if hasattr(time, 'tzset'):
+        time.tzset()
+    try:
+        retry_after = wsgiref.handlers.format_date_time(time.time())
+        with http_server(make_retry_after_handler([(429, retry_after), (200, None)])):
+            app.build()
+    finally:
+        if old_tz is None:
+            del os.environ['TZ']
+        else:
+            os.environ['TZ'] = old_tz
     content = (app.outdir / 'output.json').read_text(encoding='utf8')
     assert json.loads(content) == {
         "filename": "index.rst",