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@@ -1,5 +1,7 @@
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 *Edge*
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+* Deprecated implicit local assignments when rendering partials [Josh Peek]
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+
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 * Introduce current_cycle helper method to return the current value without bumping the cycle.  #417 [Ken Collins]
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 * Allow polymorphic_url helper to take url options. #880 [Tarmo Tänav]

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@@ -27,8 +27,14 @@ module ActionView
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     def render_partial(view, object = nil, local_assigns = {}, as = nil)
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       object ||= local_assigns[:object] ||
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-        local_assigns[variable_name] ||
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-        view.controller.instance_variable_get("@#{variable_name}") if view.respond_to?(:controller)
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+        local_assigns[variable_name]
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+
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+      if view.respond_to?(:controller)
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+        object ||= ActiveSupport::Deprecation::DeprecatedObjectProxy.new(
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+          view.controller.instance_variable_get("@#{variable_name}"),
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+          "@#{variable_name} will no longer be implicitly assigned to #{variable_name}"
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+        )
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+      end
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       # Ensure correct object is reassigned to other accessors
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       local_assigns[:object] = local_assigns[variable_name] = object

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@@ -832,8 +832,10 @@ EOS
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   end
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   def test_partial_with_implicit_local_assignment
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-    get :partial_with_implicit_local_assignment
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-    assert_equal "Hello: Marcel", @response.body
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+    assert_deprecated do
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+      get :partial_with_implicit_local_assignment
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+      assert_equal "Hello: Marcel", @response.body
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+    end
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   end
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   def test_render_missing_partial_template

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@@ -162,6 +162,22 @@ module ActiveSupport
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         end
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     end
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+    class DeprecatedObjectProxy < DeprecationProxy
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+      def initialize(object, message)
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+        @object = object
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+        @message = message
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+      end
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+
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+      private
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+        def target
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+          @object
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+        end
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+
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+        def warn(callstack, called, args)
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+          ActiveSupport::Deprecation.warn(@message, callstack)
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+        end
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+    end
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+
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     # Stand-in for <tt>@request</tt>, <tt>@attributes</tt>, <tt>@params</tt>, etc.
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     # which emits deprecation warnings on any method call (except +inspect+).
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     class DeprecatedInstanceVariableProxy < DeprecationProxy #:nodoc: