Refs #32738 -- Added sanitize_strftime_format() to replace datetime_safe.

4 files changed, 89 insertions, 7 deletions

diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index 1e67857c31..0a24e924a5 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -10,7 +10,7 @@ from itertools import chain
 
 from django.forms.utils import to_current_timezone
 from django.templatetags.static import static
-from django.utils import datetime_safe, formats
+from django.utils import formats
 from django.utils.datastructures import OrderedSet
 from django.utils.dates import MONTHS
 from django.utils.formats import get_format
@@ -1070,13 +1070,13 @@ class SelectDateWidget(Widget):
             return None
         if y is not None and m is not None and d is not None:
             input_format = get_format('DATE_INPUT_FORMATS')[0]
+            input_format = formats.sanitize_strftime_format(input_format)
             try:
                 date_value = datetime.date(int(y), int(m), int(d))
             except ValueError:
                 # Return pseudo-ISO dates with zeros for any unselected values,
                 # e.g. '2017-0-23'.
                 return '%s-%s-%s' % (y or 0, m or 0, d or 0)
-            date_value = datetime_safe.new_date(date_value)
             return date_value.strftime(input_format)
         return data.get(name)
 
diff --git a/django/utils/formats.py b/django/utils/formats.py
index 028e11415a..3bad64150a 100644
--- a/django/utils/formats.py
+++ b/django/utils/formats.py
@@ -1,10 +1,12 @@
 import datetime
 import decimal
+import functools
+import re
 import unicodedata
 from importlib import import_module
 
 from django.conf import settings
-from django.utils import dateformat, datetime_safe, numberformat
+from django.utils import dateformat, numberformat
 from django.utils.functional import lazy
 from django.utils.translation import (
     check_for_language, get_language, to_locale,
@@ -221,12 +223,12 @@ def localize_input(value, default=None):
     elif isinstance(value, (decimal.Decimal, float, int)):
         return number_format(value)
     elif isinstance(value, datetime.datetime):
-        value = datetime_safe.new_datetime(value)
         format = default or get_format('DATETIME_INPUT_FORMATS')[0]
+        format = sanitize_strftime_format(format)
         return value.strftime(format)
     elif isinstance(value, datetime.date):
-        value = datetime_safe.new_date(value)
         format = default or get_format('DATE_INPUT_FORMATS')[0]
+        format = sanitize_strftime_format(format)
         return value.strftime(format)
     elif isinstance(value, datetime.time):
         format = default or get_format('TIME_INPUT_FORMATS')[0]
@@ -234,6 +236,39 @@ def localize_input(value, default=None):
     return value
 
 
+@functools.lru_cache()
+def sanitize_strftime_format(fmt):
+    """
+    Ensure that certain specifiers are correctly padded with leading zeros.
+
+    For years < 1000 specifiers %C, %F, %G, and %Y don't work as expected for
+    strftime provided by glibc on Linux as they don't pad the year or century
+    with leading zeros. Support for specifying the padding explicitly is
+    available, however, which can be used to fix this issue.
+
+    FreeBSD, macOS, and Windows do not support explicitly specifying the
+    padding, but return four digit years (with leading zeros) as expected.
+
+    This function checks whether the %Y produces a correctly padded string and,
+    if not, makes the following substitutions:
+
+    - %C → %02C
+    - %F → %010F
+    - %G → %04G
+    - %Y → %04Y
+
+    See https://bugs.python.org/issue13305 for more details.
+    """
+    if datetime.date(1, 1, 1).strftime('%Y') == '0001':
+        return fmt
+    mapping = {'C': 2, 'F': 10, 'G': 4, 'Y': 4}
+    return re.sub(
+        r'((?:^|[^%])(?:%%)*)%([CFGY])',
+        lambda m: r'%s%%0%s%s' % (m[1], mapping[m[2]], m[2]),
+        fmt,
+    )
+
+
 def sanitize_separators(value):
     """
     Sanitize a value according to the current decimal and
diff --git a/tests/forms_tests/widget_tests/test_selectdatewidget.py b/tests/forms_tests/widget_tests/test_selectdatewidget.py
index 00cfbae758..661268a08d 100644
--- a/tests/forms_tests/widget_tests/test_selectdatewidget.py
+++ b/tests/forms_tests/widget_tests/test_selectdatewidget.py
@@ -477,7 +477,8 @@ class SelectDateWidgetTest(WidgetTest):
             w.value_from_datadict({'date_year': '1899', 'date_month': '8', 'date_day': '13'}, {}, 'date'),
             '13-08-1899',
         )
-        # And years before 1000 (demonstrating the need for datetime_safe).
+        # And years before 1000 (demonstrating the need for
+        # sanitize_strftime_format).
         w = SelectDateWidget(years=('0001',))
         self.assertEqual(
             w.value_from_datadict({'date_year': '0001', 'date_month': '8', 'date_day': '13'}, {}, 'date'),
diff --git a/tests/i18n/tests.py b/tests/i18n/tests.py
index 7d81f2a07d..7705df738c 100644
--- a/tests/i18n/tests.py
+++ b/tests/i18n/tests.py
@@ -24,7 +24,8 @@ from django.test import (
 from django.utils import translation
 from django.utils.formats import (
     date_format, get_format, get_format_modules, iter_format_modules, localize,
-    localize_input, reset_format_cache, sanitize_separators, time_format,
+    localize_input, reset_format_cache, sanitize_separators,
+    sanitize_strftime_format, time_format,
 )
 from django.utils.numberformat import format as nformat
 from django.utils.safestring import SafeString, mark_safe
@@ -1074,6 +1075,51 @@ class FormattingTests(SimpleTestCase):
                 with self.subTest(value=value):
                     self.assertEqual(localize_input(value), expected)
 
+    def test_sanitize_strftime_format(self):
+        for year in (1, 99, 999, 1000):
+            dt = datetime.date(year, 1, 1)
+            for fmt, expected in [
+                ('%C', '%02d' % (year // 100)),
+                ('%F', '%04d-01-01' % year),
+                ('%G', '%04d' % year),
+                ('%Y', '%04d' % year),
+            ]:
+                with self.subTest(year=year, fmt=fmt):
+                    fmt = sanitize_strftime_format(fmt)
+                    self.assertEqual(dt.strftime(fmt), expected)
+
+    def test_sanitize_strftime_format_with_escaped_percent(self):
+        dt = datetime.date(1, 1, 1)
+        for fmt, expected in [
+            ('%%C', '%C'),
+            ('%%F', '%F'),
+            ('%%G', '%G'),
+            ('%%Y', '%Y'),
+            ('%%%%C', '%%C'),
+            ('%%%%F', '%%F'),
+            ('%%%%G', '%%G'),
+            ('%%%%Y', '%%Y'),
+        ]:
+            with self.subTest(fmt=fmt):
+                fmt = sanitize_strftime_format(fmt)
+                self.assertEqual(dt.strftime(fmt), expected)
+
+        for year in (1, 99, 999, 1000):
+            dt = datetime.date(year, 1, 1)
+            for fmt, expected in [
+                ('%%%C', '%%%02d' % (year // 100)),
+                ('%%%F', '%%%04d-01-01' % year),
+                ('%%%G', '%%%04d' % year),
+                ('%%%Y', '%%%04d' % year),
+                ('%%%%%C', '%%%%%02d' % (year // 100)),
+                ('%%%%%F', '%%%%%04d-01-01' % year),
+                ('%%%%%G', '%%%%%04d' % year),
+                ('%%%%%Y', '%%%%%04d' % year),
+            ]:
+                with self.subTest(year=year, fmt=fmt):
+                    fmt = sanitize_strftime_format(fmt)
+                    self.assertEqual(dt.strftime(fmt), expected)
+
     def test_sanitize_separators(self):
         """
         Tests django.utils.formats.sanitize_separators.