Don't blank pad day of the month when formatting dates

We are currently using `%e` which adds a space before the result if the
digit is a single number. This leads to strings like `February  2, 2016`
which is undesireable. I've opted to replace with 0 padding instead of
removing the padding entirely, to preserve compatibility for those
relying on the fact that the width is constant, and to be consistent
with time formatting.

Fixes #25251.

activesupport/CHANGELOG.md

+*   `Date.to_s` doesn't produce too many spaces. For example, `to_s(:short)`
+    will now produce `01 Feb` instead of ` 1 Feb`.
+
+    Fixes #25251.
+
+    *Sean Griffin*
+
 *   Introduce Module#delegate_missing_to.
 
     When building a decorator, a common pattern emerges:

activesupport/lib/active_support/core_ext/date/conversions.rb

@@ -5,15 +5,15 @@
 
 class Date
   DATE_FORMATS = {
-    :short        => '%e %b',
-    :long         => '%B %e, %Y',
+    :short        => '%d %b',
+    :long         => '%B %d, %Y',
     :db           => '%Y-%m-%d',
     :number       => '%Y%m%d',
     :long_ordinal => lambda { |date|
       day_format = ActiveSupport::Inflector.ordinalize(date.day)
       date.strftime("%B #{day_format}, %Y") # => "April 25th, 2007"
     },
-    :rfc822       => '%e %b %Y',
+    :rfc822       => '%d %b %Y',
     :iso8601      => lambda { |date| date.iso8601 }
   }
 

activesupport/test/core_ext/date_ext_test.rb

@@ -30,6 +30,17 @@ def test_to_s
     assert_equal "2005-02-21",          date.to_s(:iso8601)
   end
 
+  def test_to_s_with_single_digit_day
+    date = Date.new(2005, 2, 1)
+    assert_equal "2005-02-01",          date.to_s
+    assert_equal "01 Feb",              date.to_s(:short)
+    assert_equal "February 01, 2005",   date.to_s(:long)
+    assert_equal "February 1st, 2005",  date.to_s(:long_ordinal)
+    assert_equal "2005-02-01",          date.to_s(:db)
+    assert_equal "01 Feb 2005",         date.to_s(:rfc822)
+    assert_equal "2005-02-01",          date.to_s(:iso8601)
+  end
+
   def test_readable_inspect
     assert_equal "Mon, 21 Feb 2005", Date.new(2005, 2, 21).readable_inspect
     assert_equal Date.new(2005, 2, 21).readable_inspect, Date.new(2005, 2, 21).inspect