Deprecate Hash#diff.

It's no longer used in Rails any more.

See https://github.com/rails/rails/pull/8142\#issuecomment-10227297 for more

3 files changed, 5 insertions, 3 deletions

diff --git a/actionpack/lib/action_dispatch/testing/assertions/routing.rb b/actionpack/lib/action_dispatch/testing/assertions/routing.rb
index 305bafc0c5..8f17ee05be 100644
--- a/actionpack/lib/action_dispatch/testing/assertions/routing.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions/routing.rb
@@ -1,5 +1,4 @@
 require 'uri'
-require 'active_support/core_ext/hash/diff'
 require 'active_support/core_ext/hash/indifferent_access'
 require 'action_controller/metal/exceptions'
 
@@ -44,9 +43,8 @@ module ActionDispatch
 
         expected_options.stringify_keys!
 
-        # FIXME: minitest does object diffs, do we need to have our own?
         message ||= sprintf("The recognized options <%s> did not match <%s>, difference: <%s>",
-            request.path_parameters, expected_options, expected_options.diff(request.path_parameters))
+            request.path_parameters, expected_options, diff(expected_options, request.path_parameters))
         assert_equal(expected_options, request.path_parameters, message)
       end
 
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 61d85543d1..dc84b44dec 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,4 +1,7 @@
 ## Rails 4.0.0 (unreleased) ##
+
+*   Deprecate Hash#diff in favor of MiniTest's #diff. *Steve Klabnik*
+
 *   Kernel#capture can catch output from subprocesses *Dmitry Vorotilin*
 
 *   `to_xml` conversions now use builder's `tag!` method instead of explicit invocation of `method_missing`.
diff --git a/activesupport/lib/active_support/core_ext/hash/diff.rb b/activesupport/lib/active_support/core_ext/hash/diff.rb
index 831dee8ecb..a27c55479a 100644
--- a/activesupport/lib/active_support/core_ext/hash/diff.rb
+++ b/activesupport/lib/active_support/core_ext/hash/diff.rb
@@ -6,6 +6,7 @@ class Hash
   #   {}.diff(1 => 2)               # => {1 => 2}
   #   {1 => 2, 3 => 4}.diff(1 => 2) # => {3 => 4}
   def diff(other)
+    ActiveSupport::Deprecation.warn "Hash#diff is no longer used inside of Rails, and is being deprecated with no replacement. If you're using it to compare hashes for the purpose of testing, please use MiniTest's diff instead."
     dup.
       delete_if { |k, v| other[k] == v }.
       merge!(other.dup.delete_if { |k, v| has_key?(k) })