From f1b2682d58f997fd26ed4d7df59d1910ce464203 Mon Sep 17 00:00:00 2001
From: Adam Turner <9087854+aa-turner@users.noreply.github.com>
Date: Sun, 13 Aug 2023 19:38:34 +0100
Subject: [PATCH] Format modified times without ``datetime``

---
 sphinx/builders/html/__init__.py | 18 +++++++++++-------
 sphinx/environment/__init__.py   | 24 +++++++++++-------------
 2 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/sphinx/builders/html/__init__.py b/sphinx/builders/html/__init__.py
index 5e20f7100..425d7bfa1 100644
--- a/sphinx/builders/html/__init__.py
+++ b/sphinx/builders/html/__init__.py
@@ -8,8 +8,8 @@ import os
 import posixpath
 import re
 import sys
+import time
 import warnings
-from datetime import datetime, timezone
 from os import path
 from typing import IO, TYPE_CHECKING, Any
 from urllib.parse import quote
@@ -397,17 +397,15 @@ class StandaloneHTMLBuilder(Builder):
             except Exception:
                 targetmtime = 0
             try:
-                srcmtime = max(path.getmtime(self.env.doc2path(docname)),
-                               template_mtime)
+                srcmtime = max(path.getmtime(self.env.doc2path(docname)), template_mtime)
                 if srcmtime > targetmtime:
                     logger.debug(
                         '[build target] targetname %r(%s), template(%s), docname %r(%s)',
                         targetname,
-                        datetime.fromtimestamp(targetmtime, tz=timezone.utc),
-                        datetime.fromtimestamp(template_mtime, tz=timezone.utc),
+                        _format_modified_time(targetmtime),
+                        _format_modified_time(template_mtime),
                         docname,
-                        datetime.fromtimestamp(path.getmtime(self.env.doc2path(docname)),
-                                               tz=timezone.utc),
+                        _format_modified_time(path.getmtime(self.env.doc2path(docname))),
                     )
                     yield docname
             except OSError:
@@ -1192,6 +1190,12 @@ def convert_html_css_files(app: Sphinx, config: Config) -> None:
     config.html_css_files = html_css_files  # type: ignore[attr-defined]
 
 
+def _format_modified_time(timestamp: float) -> str:
+    """Return an RFC 3339 formatted string representing the given timestamp."""
+    seconds, fraction = divmod(timestamp, 1)
+    return time.strftime("%Y-%m-%d %H:%M:%S", time.gmtime(seconds)) + f'.{fraction:.3f}'
+
+
 def convert_html_js_files(app: Sphinx, config: Config) -> None:
     """This converts string styled html_js_files to tuple styled one."""
     html_js_files: list[tuple[str, dict]] = []
diff --git a/sphinx/environment/__init__.py b/sphinx/environment/__init__.py
index 04c46f2e5..13a0ae400 100644
--- a/sphinx/environment/__init__.py
+++ b/sphinx/environment/__init__.py
@@ -5,9 +5,9 @@ from __future__ import annotations
 import functools
 import os
 import pickle
+import time
 from collections import defaultdict
 from copy import copy
-from datetime import datetime, timezone
 from os import path
 from typing import TYPE_CHECKING, Any, Callable
 
@@ -488,12 +488,9 @@ class BuildEnvironment:
                 mtime = self.all_docs[docname]
                 newmtime = _last_modified_time(self.doc2path(docname))
                 if newmtime > mtime:
-                    # convert integer microseconds to floating-point seconds,
-                    # and then to timezone-aware datetime objects.
-                    mtime_dt = datetime.fromtimestamp(mtime / 1_000_000, tz=timezone.utc)
-                    newmtime_dt = datetime.fromtimestamp(mtime / 1_000_000, tz=timezone.utc)
                     logger.debug('[build target] outdated %r: %s -> %s',
-                                 docname, mtime_dt, newmtime_dt)
+                                 docname,
+                                 _format_modified_time(mtime), _format_modified_time(newmtime))
                     changed.add(docname)
                     continue
                 # finally, check the mtime of dependencies
@@ -510,15 +507,10 @@ class BuildEnvironment:
                             break
                         depmtime = _last_modified_time(deppath)
                         if depmtime > mtime:
-                            mtime_dt = datetime.fromtimestamp(
-                                mtime / 1_000_000, tz=timezone.utc,
-                            )
-                            depmtime_dt = datetime.fromtimestamp(
-                                depmtime / 1_000_000, tz=timezone.utc,
-                            )
                             logger.debug(
                                 '[build target] outdated %r from dependency %r: %s -> %s',
-                                docname, deppath, mtime_dt, depmtime_dt,
+                                docname, deppath,
+                                _format_modified_time(mtime), _format_modified_time(depmtime),
                             )
                             changed.add(docname)
                             break
@@ -748,6 +740,12 @@ def _last_modified_time(filename: str | os.PathLike[str]) -> int:
     return -(os.stat(filename).st_mtime_ns // -1_000)
 
 
+def _format_modified_time(timestamp: int) -> str:
+    """Return an RFC 3339 formatted string representing the given timestamp."""
+    seconds, fraction = divmod(timestamp, 10**6)
+    return time.strftime("%Y-%m-%d %H:%M:%S", time.gmtime(seconds)) + f'.{fraction//1_000}'
+
+
 def _traverse_toctree(
     traversed: set[str],
     parent: str | None,