Make `button_to` more model-aware

Infer HTTP verb `[method]` from a model or Array with model as the first
argument to `button_to` when combined with a block:

```ruby
button_to(Workshop.find(1)){ "Update" }
  #=> <form method="post" action="/workshops/1" class="button_to">
  #=>   <input type="hidden" name="_method" value="patch" autocomplete="off" />
  #=>   <button type="submit">Update</button>
  #=> </form>

button_to([ Workshop.find(1), Session.find(1) ]) { "Update" }
  #=> <form method="post" action="/workshops/1/sessions/1" class="button_to">
  #=>   <input type="hidden" name="_method" value="patch" autocomplete="off" />
  #=>   <button type="submit">Update</button>
  #=> </form>
```

Prior to this change, the constructed `<form>` was always submitted with
a `[method="post"]` and _always_ omitted the `<input type="hidden"
name="_method" value="...">` field, regardless of the return value of
the "model" argument's `#persisted?` predicate.

actionview/CHANGELOG.md

@@ -1,3 +1,22 @@
+*   Infer HTTP verb `[method]` from a model or Array with model as the first
+    argument to `button_to` when combined with a block:
+
+    ```ruby
+    button_to(Workshop.find(1)){ "Update" }
+    #=> <form method="post" action="/workshops/1" class="button_to">
+    #=>   <input type="hidden" name="_method" value="patch" autocomplete="off" />
+    #=>   <button type="submit">Update</button>
+    #=> </form>
+
+    button_to([ Workshop.find(1), Session.find(1) ]) { "Update" }
+    #=> <form method="post" action="/workshops/1/sessions/1" class="button_to">
+    #=>   <input type="hidden" name="_method" value="patch" autocomplete="off" />
+    #=>   <button type="submit">Update</button>
+    #=> </form>
+    ```
+
+    *Sean Doyle*
+
 *   Add `:day_format` option to `date_select`
 
         date_select("article", "written_on", day_format: ->(day) { day.ordinalize })

actionview/lib/action_view/helpers/url_helper.rb

@@ -332,7 +332,8 @@ module ActionView
         remote = html_options.delete("remote")
         params = html_options.delete("params")
 
-        method     = html_options.delete("method").to_s
+        method     = (html_options.delete("method").presence || method_for_options(options)).to_s
+
         method_tag = BUTTON_TAG_METHOD_VERBS.include?(method) ? method_tag(method) : "".html_safe
 
         form_method  = method == "get" ? "get" : "post"
@@ -753,6 +754,16 @@ module ActionView
           html_options["data-method"] = method
         end
 
+        def method_for_options(options)
+          if options.is_a?(Array)
+            method_for_options(options.last)
+          elsif options.respond_to?(:persisted?)
+            options.persisted? ? :patch : :post
+          elsif options.respond_to?(:to_model)
+            method_for_options(options.to_model)
+          end
+        end
+
         STRINGIFIED_COMMON_METHODS = {
           get:    "get",
           delete: "delete",

actionview/test/template/url_helper_test.rb

@@ -35,7 +35,10 @@ class UrlHelperTest < ActiveSupport::TestCase
     get "/other" => "foo#other"
     get "/article/:id" => "foo#article", :as => :article
     get "/category/:category" => "foo#category"
-    resources :workshops
+    resources :sessions
+    resources :workshops do
+      resources :sessions
+    end
 
     scope :engine do
       get "/" => "foo#bar"
@@ -161,6 +164,62 @@ class UrlHelperTest < ActiveSupport::TestCase
     )
   end
 
+  def test_button_to_with_new_record_model
+    session = Session.new(nil)
+
+    assert_dom_equal(
+      %{<form method="post" action="/sessions" class="button_to"><button type="submit">Create Session</button></form>},
+      button_to("Create Session", session)
+    )
+  end
+
+  def test_button_to_with_new_record_model_and_block
+    workshop = Workshop.new(nil)
+
+    assert_dom_equal(
+      %{<form method="post" action="/workshops" class="button_to"><button type="submit">Create</button></form>},
+      button_to(workshop) { "Create" }
+    )
+  end
+
+  def test_button_to_with_nested_new_record_model_and_block
+    workshop = Workshop.new("1")
+    session = Session.new(nil)
+
+    assert_dom_equal(
+      %{<form method="post" action="/workshops/1/sessions" class="button_to"><button type="submit">Create</button></form>},
+      button_to([workshop, session]) { "Create" }
+    )
+  end
+
+  def test_button_to_with_persisted_model
+    workshop = Workshop.new("1")
+
+    assert_dom_equal(
+      %{<form method="post" action="/workshops/1" class="button_to"><input type="hidden" name="_method" value="patch" autocomplete="off" /><button type="submit">Update</button></form>},
+      button_to(workshop) { "Update" }
+    )
+  end
+
+  def test_button_to_with_persisted_model_and_block
+    workshop = Workshop.new("1")
+
+    assert_dom_equal(
+      %{<form method="post" action="/workshops/1" class="button_to"><input type="hidden" name="_method" value="patch" autocomplete="off" /><button type="submit">Update</button></form>},
+      button_to(workshop) { "Update" }
+    )
+  end
+
+  def test_button_to_with_nested_persisted_model_and_block
+    workshop = Workshop.new("1")
+    session = Session.new("1")
+
+    assert_dom_equal(
+      %{<form method="post" action="/workshops/1/sessions/1" class="button_to"><input type="hidden" name="_method" value="patch" autocomplete="off" /><button type="submit">Update</button></form>},
+      button_to([workshop, session]) { "Update" }
+    )
+  end
+
   def test_button_to_with_straight_url_and_request_forgery
     self.request_forgery = true