[1.10.x] Fixed #27637 -- Fixed timesince, timeuntil in leap year edge case.

Backport of 3e5c5e6754 from master

django/utils/timesince.py

@@ -40,10 +40,15 @@ def timesince(d, now=None, reversed=False):
     if not now:
         now = datetime.datetime.now(utc if is_aware(d) else None)
 
-    delta = (d - now) if reversed else (now - d)
+    if reversed:
+        d, now = now, d
+    delta = now - d
 
     # Deal with leapyears by subtracing the number of leapdays
-    delta -= datetime.timedelta(calendar.leapdays(d.year, now.year))
+    leapdays = calendar.leapdays(d.year, now.year)
+    if leapdays != 0 and calendar.isleap(d.year):
+        leapdays -= 1
+    delta -= datetime.timedelta(leapdays)
 
     # ignore microseconds
     since = delta.days * 24 * 60 * 60 + delta.seconds

docs/releases/1.10.5.txt

@@ -14,3 +14,6 @@ Bugfixes
 
 * Fixed occasional missing plural forms in ``JavaScriptCatalog``
   (:ticket:`27418`).
+
+* Fixed a regression in the ``timesince`` and ``timeuntil`` filters that caused
+  incorrect results for dates in a leap year.

docs/releases/1.9.13.txt

@@ -0,0 +1,13 @@
+===========================
+Django 1.9.13 release notes
+===========================
+
+*Under development*
+
+Django 1.9.13 fixes a bug in 1.9.12.
+
+Bugfixes
+========
+
+* Fixed a regression in the ``timesince`` and ``timeuntil`` filters that caused
+  incorrect results for dates in a leap year.

docs/releases/index.txt

@@ -37,6 +37,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   1.9.13
    1.9.12
    1.9.11
    1.9.10

tests/utils_tests/test_timesince.py

@@ -105,6 +105,11 @@ class TimesinceTests(unittest.TestCase):
         self.assertEqual(timeuntil(today - self.oneday, today), '0\xa0minutes')
         self.assertEqual(timeuntil(today + self.oneweek, today), '1\xa0week')
 
+    def test_leap_year(self):
+        start_date = datetime.date(2016, 12, 25)
+        self.assertEqual(timeuntil(start_date + self.oneweek, start_date), '1\xa0week')
+        self.assertEqual(timesince(start_date, start_date + self.oneweek), '1\xa0week')
+
     def test_naive_datetime_with_tzinfo_attribute(self):
         class naive(datetime.tzinfo):
             def utcoffset(self, dt):
@@ -117,3 +122,4 @@ class TimesinceTests(unittest.TestCase):
     def test_thousand_years_ago(self):
         t = datetime.datetime(1007, 8, 14, 13, 46, 0)
         self.assertEqual(timesince(t, self.t), '1000\xa0years')
+        self.assertEqual(timeuntil(self.t, t), '1000\xa0years')