Support symbols in :cache_path option

This tiny commit allows to use symbols in the `:cache_path` option via
the standard behavior of `Symbol#to_proc`. The controller's instance
method pointed by the symbol should be in a `protected` scope.

Author: estum

lib/action_controller/caching/actions.rb

@@ -154,7 +154,7 @@ def initialize(options, &block)
         def around(controller)
           cache_layout = @cache_layout.respond_to?(:call) ? @cache_layout.call(controller) : @cache_layout
 
-          path_options = if @cache_path.is_a?(Proc)
+          path_options = if @cache_path.is_a?(Proc) || @cache_path.respond_to?(:to_proc)
             controller.instance_exec(controller, &@cache_path)
           elsif @cache_path.respond_to?(:call)
             @cache_path.call(controller)

test/caching_test.rb

@@ -35,6 +35,7 @@ class ActionCachingTestController < CachingController
   caches_action :show, cache_path: 'http://test.host/custom/show'
   caches_action :edit, cache_path: Proc.new { |c| c.params[:id] ? "http://test.host/#{c.params[:id]};edit" : 'http://test.host/edit' }
   caches_action :custom_cache_path, cache_path: CachePath.new
+  caches_action :symbol_cache_path, cache_path: :cache_path_protected_method
   caches_action :with_layout
   caches_action :with_format_and_http_param, cache_path: Proc.new { |c| { key: 'value' } }
   caches_action :with_symbol_format, cache_path: 'http://test.host/action_caching_test/with_symbol_format'
@@ -92,6 +93,7 @@ def simple_runtime_error
   alias_method :edit, :index
   alias_method :destroy, :index
   alias_method :custom_cache_path, :index
+  alias_method :symbol_cache_path, :index
   alias_method :layout_false, :with_layout
   alias_method :with_layout_proc_param, :with_layout
 
@@ -121,6 +123,12 @@ def invalid
       format.json{ render json: @cache_this }
     end
   end
+
+  protected
+
+  def cache_path_protected_method
+    ['controller', params[:id]].compact.join('-')
+  end
 end
 
 class MockTime < Time
@@ -327,6 +335,16 @@ def test_action_cache_with_custom_cache_path_with_custom_object
     assert fragment_exist?('controller-1')
   end
 
+  def test_action_cache_with_symbol_cache_path
+    get :symbol_cache_path
+    assert_response :success
+    assert fragment_exist?('controller')
+
+    get :symbol_cache_path, id: 1
+    assert_response :success
+    assert fragment_exist?('controller-1')
+  end
+
   def test_cache_expiration
     get :index
     assert_response :success