Merge branch 'master' into treewip

* master:
  eliminate warnings about multiple primary keys on habtm join tables
  Add methods to array delegation from `Relation`
  Fix button_to's params option to support nested names.
  Dependencies clean up
  Deprecate AC::Parameters#== with a Hash
  Fix AC::Parameters#== with other AC::Parameters
  Tests for AC::Parameters#==
  better docs for ActiveSupport::TestCase#assert_nothing_raised
  remove needless `debug_exception_response_format` config [ci skip]
  partial pass over the API guide [ci skip]
  Fix `unsubscribed` server side behavior
  Use a semaphore to signal message availability
  Fix master build
  Remove github gems from the master bug report templates
  Truncate ActionCable broadcast message to 300 chars
  Remove unused require

3 files changed, 86 insertions, 4 deletions

diff --git a/actionview/CHANGELOG.md b/actionview/CHANGELOG.md
index bebe78c360..461a26b10b 100644
--- a/actionview/CHANGELOG.md
+++ b/actionview/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Fix `button_to`'s `:params` option support to correctly generated input names for nested hashes/arrays.
+
+    *James Coleman*
+
 ## Rails 5.0.0.beta2 (February 01, 2016) ##
 
 *   Fix stripping the digest from the automatically generated img tag alt
diff --git a/actionview/lib/action_view/helpers/url_helper.rb b/actionview/lib/action_view/helpers/url_helper.rb
index 3a4561a083..87218821ed 100644
--- a/actionview/lib/action_view/helpers/url_helper.rb
+++ b/actionview/lib/action_view/helpers/url_helper.rb
@@ -329,8 +329,8 @@ module ActionView
 
         inner_tags = method_tag.safe_concat(button).safe_concat(request_token_tag)
         if params
-          params.each do |param_name, value|
-            inner_tags.safe_concat tag(:input, type: "hidden", name: param_name, value: value.to_param)
+          to_form_params(params).each do |param|
+            inner_tags.safe_concat tag(:input, type: "hidden", name: param[:name], value: param[:value])
           end
         end
         content_tag('form', inner_tags, form_options)
@@ -595,6 +595,42 @@ module ActionView
         def method_tag(method)
           tag('input', type: 'hidden', name: '_method', value: method.to_s)
         end
+
+        # Returns an array of hashes each containing :name and :value keys
+        # suitable for use as the names and values of form input fields:
+        #
+        #   to_form_params(name: 'David', nationality: 'Danish')
+        #   # => [{name: :name, value: 'David'}, {name: 'nationality', value: 'Danish'}]
+        #
+        #   to_form_params(country: {name: 'Denmark'})
+        #   # => [{name: 'country[name]', value: 'Denmark'}]
+        #
+        #   to_form_params(countries: ['Denmark', 'Sweden']})
+        #   # => [{name: 'countries[]', value: 'Denmark'}, {name: 'countries[]', value: 'Sweden'}]
+        #
+        # An optional namespace can be passed to enclose key names:
+        #
+        #   to_form_params({ name: 'Denmark' }, 'country')
+        #   # => [{name: 'country[name]', value: 'Denmark'}]
+        def to_form_params(attribute, namespace = nil) # :nodoc:
+          params = []
+          case attribute
+          when Hash
+            attribute.each do |key, value|
+              prefix = namespace ? "#{namespace}[#{key}]" : key
+              params.push(*to_form_params(value, prefix))
+            end
+          when Array
+            array_prefix = "#{namespace}[]"
+            attribute.each do |value|
+              params.push(*to_form_params(value, array_prefix))
+            end
+          else
+            params << { name: namespace, value: attribute.to_param }
+          end
+
+          params.sort_by { |pair| pair[:name] }
+        end
     end
   end
 end
diff --git a/actionview/test/template/url_helper_test.rb b/actionview/test/template/url_helper_test.rb
index 3010656166..d6a19a829f 100644
--- a/actionview/test/template/url_helper_test.rb
+++ b/actionview/test/template/url_helper_test.rb
@@ -71,6 +71,34 @@ class UrlHelperTest < ActiveSupport::TestCase
     assert_equal 'javascript:history.back()', url_for(:back)
   end
 
+  def test_to_form_params_with_hash
+    assert_equal(
+      [{ name: :name, value: 'David' }, { name: :nationality, value: 'Danish' }],
+      to_form_params(name: 'David', nationality: 'Danish')
+    )
+  end
+
+  def test_to_form_params_with_nested_hash
+    assert_equal(
+      [{ name: 'country[name]', value: 'Denmark' }],
+      to_form_params(country: { name: 'Denmark' })
+    )
+  end
+
+  def test_to_form_params_with_array_nested_in_hash
+    assert_equal(
+      [{ name: 'countries[]', value: 'Denmark' }, { name: 'countries[]', value: 'Sweden' }],
+      to_form_params(countries: ['Denmark', 'Sweden'])
+    )
+  end
+
+  def test_to_form_params_with_namespace
+    assert_equal(
+      [{ name: 'country[name]', value: 'Denmark' }],
+      to_form_params({name: 'Denmark'}, 'country')
+    )
+  end
+
   def test_button_to_with_straight_url
     assert_dom_equal %{<form method="post" action="http://www.example.com" class="button_to"><input type="submit" value="Hello" /></form>}, button_to("Hello", "http://www.example.com")
   end
@@ -189,8 +217,22 @@ class UrlHelperTest < ActiveSupport::TestCase
 
   def test_button_to_with_params
     assert_dom_equal(
-      %{<form action="http://www.example.com" class="button_to" method="post"><input type="submit" value="Hello" /><input type="hidden" name="foo" value="bar" /><input type="hidden" name="baz" value="quux" /></form>},
-      button_to("Hello", "http://www.example.com", params: {foo: :bar, baz: "quux"})
+      %{<form action="http://www.example.com" class="button_to" method="post"><input type="submit" value="Hello" /><input type="hidden" name="baz" value="quux" /><input type="hidden" name="foo" value="bar" /></form>},
+      button_to("Hello", "http://www.example.com", params: { foo: :bar, baz: "quux" })
+    )
+  end
+
+  def test_button_to_with_nested_hash_params
+    assert_dom_equal(
+      %{<form action="http://www.example.com" class="button_to" method="post"><input type="submit" value="Hello" /><input type="hidden" name="foo[bar]" value="baz" /></form>},
+      button_to("Hello", "http://www.example.com", params: { foo: { bar: 'baz' } })
+    )
+  end
+
+  def test_button_to_with_nested_array_params
+    assert_dom_equal(
+      %{<form action="http://www.example.com" class="button_to" method="post"><input type="submit" value="Hello" /><input type="hidden" name="foo[]" value="bar" /></form>},
+      button_to("Hello", "http://www.example.com", params: { foo: ['bar'] })
     )
   end