7 files changed, 67 insertions, 22 deletions
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 435c863025..14435649cd 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,30 @@
+*   Add same method signature for `Time#prev_month` and `Time#next_month`
+    in accordance with `Date#prev_month`, `Date#next_month`.
+
+    Allows pass argument for `Time#prev_month` and `Time#next_month`.
+
+    Before:
+    ```
+    Time.new(2017, 9, 16, 17, 0).prev_month    # => 2017-08-16 17:00:00 +0300
+    Time.new(2017, 9, 16, 17, 0).prev_month(1)
+    # => ArgumentError: wrong number of arguments (given 1, expected 0)
+
+    Time.new(2017, 9, 16, 17, 0).next_month    # => 2017-10-16 17:00:00 +0300
+    Time.new(2017, 9, 16, 17, 0).next_month(1)
+    # => ArgumentError: wrong number of arguments (given 1, expected 0)
+    ```
+
+    After:
+    ```
+    Time.new(2017, 9, 16, 17, 0).prev_month    # => 2017-08-16 17:00:00 +0300
+    Time.new(2017, 9, 16, 17, 0).prev_month(1) # => 2017-08-16 17:00:00 +0300
+
+    Time.new(2017, 9, 16, 17, 0).next_month    # => 2017-10-16 17:00:00 +0300
+    Time.new(2017, 9, 16, 17, 0).next_month(1) # => 2017-10-16 17:00:00 +0300
+    ```
+
+    *bogdanvlviv*
+
 *   Add same method signature for `Time#prev_day` and `Time#next_day`
     in accordance with `Date#prev_day`, `Date#next_day`.
 
diff --git a/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb b/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb
index 9b5477b199..59c87b9c06 100644
--- a/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb
+++ b/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb
@@ -188,9 +188,9 @@ module DateAndTime
       end
     end
 
-    # Short-hand for months_since(1).
-    def next_month
-      months_since(1)
+    # Returns a new date/time the specified number of months in the future.
+    def next_month(months = 1)
+      advance(months: months)
     end
 
     # Short-hand for months_since(3)
@@ -223,11 +223,15 @@ module DateAndTime
     end
     alias_method :last_weekday, :prev_weekday
 
+    # Returns a new date/time the specified number of months ago.
+    def prev_month(months = 1)
+      advance(months: -months)
+    end
+
     # Short-hand for months_ago(1).
-    def prev_month
+    def last_month
       months_ago(1)
     end
-    alias_method :last_month, :prev_month
 
     # Short-hand for months_ago(3).
     def prev_quarter
diff --git a/activesupport/test/core_ext/date_and_time_behavior.rb b/activesupport/test/core_ext/date_and_time_behavior.rb
index 438eb8b755..091d5611d0 100644
--- a/activesupport/test/core_ext/date_and_time_behavior.rb
+++ b/activesupport/test/core_ext/date_and_time_behavior.rb
@@ -161,6 +161,16 @@ module DateAndTimeBehavior
     assert_equal date_time_init(2015, 1, 5, 15, 15, 10), date_time_init(2015, 1, 3, 15, 15, 10).next_weekday
   end
 
+  def test_next_month
+    assert_equal date_time_init(2004, 12, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month(-2)
+    assert_equal date_time_init(2005, 1, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month(-1)
+    assert_equal date_time_init(2005, 2, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month(0)
+    assert_equal date_time_init(2005, 3, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month(1)
+    assert_equal date_time_init(2005, 4, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month(2)
+    assert_equal date_time_init(2005, 3, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month
+    assert_equal date_time_init(2005, 4, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).next_month.next_month
+  end
+
   def test_next_month_on_31st
     assert_equal date_time_init(2005, 9, 30, 15, 15, 10), date_time_init(2005, 8, 31, 15, 15, 10).next_month
   end
@@ -213,6 +223,16 @@ module DateAndTimeBehavior
     assert_equal date_time_init(2015, 1, 2, 15, 15, 10), date_time_init(2015, 1, 4, 15, 15, 10).prev_weekday
   end
 
+  def test_prev_month
+    assert_equal date_time_init(2005, 4, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month(-2)
+    assert_equal date_time_init(2005, 3, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month(-1)
+    assert_equal date_time_init(2005, 2, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month(0)
+    assert_equal date_time_init(2005, 1, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month(1)
+    assert_equal date_time_init(2004, 12, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month(2)
+    assert_equal date_time_init(2005, 1, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month
+    assert_equal date_time_init(2004, 12, 22, 10, 10, 10), date_time_init(2005, 2, 22, 10, 10, 10).prev_month.prev_month
+  end
+
   def test_prev_month_on_31st
     assert_equal date_time_init(2004, 2, 29, 10, 10, 10), date_time_init(2004, 3, 31, 10, 10, 10).prev_month
   end
@@ -225,6 +245,10 @@ module DateAndTimeBehavior
     assert_equal date_time_init(2004, 6, 5, 10, 10, 10),  date_time_init(2005, 6, 5, 10, 10, 10).prev_year
   end
 
+  def test_last_month_on_31st
+    assert_equal date_time_init(2004, 2, 29, 0, 0, 0), date_time_init(2004, 3, 31, 0, 0, 0).last_month
+  end
+
   def test_days_to_week_start
     assert_equal 0, date_time_init(2011, 11, 01, 0, 0, 0).days_to_week_start(:tuesday)
     assert_equal 1, date_time_init(2011, 11, 02, 0, 0, 0).days_to_week_start(:tuesday)
diff --git a/activesupport/test/core_ext/date_ext_test.rb b/activesupport/test/core_ext/date_ext_test.rb
index b8672eac4b..1d05ac6157 100644
--- a/activesupport/test/core_ext/date_ext_test.rb
+++ b/activesupport/test/core_ext/date_ext_test.rb
@@ -185,10 +185,6 @@ class DateExtCalculationsTest < ActiveSupport::TestCase
     assert_equal Date.new(1582, 10, 18), Date.new(1582, 10, 4).next_week
   end
 
-  def test_last_month_on_31st
-    assert_equal Date.new(2004, 2, 29), Date.new(2004, 3, 31).last_month
-  end
-
   def test_last_quarter_on_31st
     assert_equal Date.new(2004, 2, 29), Date.new(2004, 5, 31).last_quarter
   end
diff --git a/activesupport/test/core_ext/date_time_ext_test.rb b/activesupport/test/core_ext/date_time_ext_test.rb
index a3c2018a31..a795ed0102 100644
--- a/activesupport/test/core_ext/date_time_ext_test.rb
+++ b/activesupport/test/core_ext/date_time_ext_test.rb
@@ -248,10 +248,6 @@ class DateTimeExtCalculationsTest < ActiveSupport::TestCase
     assert_equal DateTime.civil(2016, 2, 29), DateTime.civil(2016, 3, 7).last_week
   end
 
-  def test_last_month_on_31st
-    assert_equal DateTime.civil(2004, 2, 29), DateTime.civil(2004, 3, 31).last_month
-  end
-
   def test_last_quarter_on_31st
     assert_equal DateTime.civil(2004, 2, 29), DateTime.civil(2004, 5, 31).last_quarter
   end
diff --git a/activesupport/test/core_ext/time_ext_test.rb b/activesupport/test/core_ext/time_ext_test.rb
index dc2f4c5ac7..b720e32022 100644
--- a/activesupport/test/core_ext/time_ext_test.rb
+++ b/activesupport/test/core_ext/time_ext_test.rb
@@ -664,10 +664,6 @@ class TimeExtCalculationsTest < ActiveSupport::TestCase
     end
   end
 
-  def test_last_month_on_31st
-    assert_equal Time.local(2004, 2, 29), Time.local(2004, 3, 31).last_month
-  end
-
   def test_xmlschema_is_available
     assert_nothing_raised { Time.now.xmlschema }
   end
diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index 54d3dec1c2..ae64ad93d6 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -3019,11 +3019,9 @@ Date.new(2000, 5, 31).next_month # => Fri, 30 Jun 2000
 Date.new(2000, 1, 31).next_month # => Tue, 29 Feb 2000
 ```
 
-`prev_month` is aliased to `last_month`.
-
 ##### `prev_quarter`, `next_quarter`
 
-Same as `prev_month` and `next_month`. It returns the date with the same day in the previous or next quarter:
+`prev_quarter` and `next_quarter` return the date with the same day in the previous or next quarter:
 
 ```ruby
 t = Time.local(2010, 5, 8) # => Sat, 08 May 2010
@@ -3175,6 +3173,8 @@ Date.new(2010, 4, 30).months_ago(2)    # => Sun, 28 Feb 2010
 Date.new(2009, 12, 31).months_since(2) # => Sun, 28 Feb 2010
 ```
 
+`last_month` is short-hand for `#months_ago(1)`.
+
 ##### `weeks_ago`
 
 The method `weeks_ago` works analogously for weeks:
@@ -3353,8 +3353,9 @@ months_ago
 months_since
 beginning_of_month (at_beginning_of_month)
 end_of_month (at_end_of_month)
-prev_month (last_month)
+prev_month
 next_month
+last_month
 beginning_of_quarter (at_beginning_of_quarter)
 end_of_quarter (at_end_of_quarter)
 beginning_of_year (at_beginning_of_year)
@@ -3541,8 +3542,9 @@ months_ago
 months_since
 beginning_of_month (at_beginning_of_month)
 end_of_month (at_end_of_month)
-prev_month (last_month)
+prev_month
 next_month
+last_month
 beginning_of_quarter (at_beginning_of_quarter)
 end_of_quarter (at_end_of_quarter)
 beginning_of_year (at_beginning_of_year)