Fixed #14711 -- Corrected the calculation for the previous month in generic date views. Thanks to msundstr for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15438 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/views/generic/dates.py

@@ -70,7 +70,7 @@ class MonthMixin(object):
         Get the previous valid month.
         """
         first_day, last_day = _month_bounds(date)
-        prev = (first_day - datetime.timedelta(days=1)).replace(day=1)
+        prev = (first_day - datetime.timedelta(days=1))
         return _get_next_prev_month(self, prev, is_previous=True, use_first_day=True)
 
 
@@ -516,7 +516,7 @@ def _get_next_prev_month(generic_view, naive_result, is_previous, use_first_day)
     This is a bit complicated since it handles both next and previous months
     and days (for MonthArchiveView and DayArchiveView); hence the coupling to generic_view.
 
-    However in essance the logic comes down to:
+    However in essence the logic comes down to:
 
         * If allow_empty and allow_future are both true, this is easy: just
           return the naive result (just the next/previous day or month,
@@ -546,7 +546,7 @@ def _get_next_prev_month(generic_view, naive_result, is_previous, use_first_day)
     # whose date_field is at least (greater than/less than) the given
     # naive result
     else:
-        # Construct a lookup and an ordering depending on weather we're doing
+        # Construct a lookup and an ordering depending on whether we're doing
         # a previous date or a next date lookup.
         if is_previous:
             lookup = {'%s__lte' % date_field: naive_result}
@@ -569,7 +569,7 @@ def _get_next_prev_month(generic_view, naive_result, is_previous, use_first_day)
         result = result.date()
 
     # For month views, we always want to have a date that's the first of the
-    # month for consistancy's sake.
+    # month for consistency's sake.
     if result and use_first_day:
         result = result.replace(day=1)
 

tests/regressiontests/generic_views/dates.py

@@ -198,6 +198,29 @@ class MonthArchiveViewTests(TestCase):
         res = self.client.get('/dates/books/2007/no_month/')
         self.assertEqual(res.status_code, 404)
 
+    def test_previous_month_without_content(self):
+        "Content can exist on any day of the previous month. Refs #14711"
+        self.pubdate_list = [
+            datetime.date(2010, month, day)
+            for month,day in ((9,1), (10,2), (11,3))
+        ]
+        for pubdate in self.pubdate_list:
+            name = str(pubdate)
+            Book.objects.create(name=name, slug=name, pages=100, pubdate=pubdate)
+
+        res = self.client.get('/dates/books/2010/nov/allow_empty/')
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.context['previous_month'], datetime.date(2010,10,1))
+        # The following test demonstrates the bug
+        res = self.client.get('/dates/books/2010/nov/')
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.context['previous_month'], datetime.date(2010,10,1))
+        # The bug does not occur here because a Book with pubdate of Sep 1 exists
+        res = self.client.get('/dates/books/2010/oct/')
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.context['previous_month'], datetime.date(2010,9,1))
+
+
 class WeekArchiveViewTests(TestCase):
     fixtures = ['generic-views-test-data.json']
     urls = 'regressiontests.generic_views.urls'
@@ -359,3 +382,4 @@ class DateDetailViewTests(TestCase):
 
     def test_invalid_url(self):
         self.assertRaises(AttributeError, self.client.get, "/dates/books/2008/oct/01/nopk/")
+