clear cache on body close so that cache remains during rendering

fixes #13547

The body may use the local cache during rendering.  `call`ing the app
doesn't mean that rendering is finished, so we need to wait until
`close` is called on the body.

activesupport/lib/active_support/cache/strategy/local_cache.rb

@@ -1,5 +1,6 @@
 require 'active_support/core_ext/object/duplicable'
 require 'active_support/core_ext/string/inflections'
+require 'rack/body_proxy'
 
 module ActiveSupport
   module Cache
@@ -83,9 +84,14 @@ def new(app)
 
           def call(env)
             LocalCacheRegistry.set_cache_for(local_cache_key, LocalStore.new)
-            @app.call(env)
-          ensure
+            response = @app.call(env)
+            response[2] = ::Rack::BodyProxy.new(response[2]) do
+              LocalCacheRegistry.set_cache_for(local_cache_key, nil)
+            end
+            response
+          rescue Exception
             LocalCacheRegistry.set_cache_for(local_cache_key, nil)
+            raise
           end
         end
 

activesupport/test/caching_test.rb

@@ -3,6 +3,42 @@
 require 'active_support/cache'
 require 'dependencies_test_helpers'
 
+module ActiveSupport
+  module Cache
+    module Strategy
+      module LocalCache
+        class MiddlewareTest < ActiveSupport::TestCase
+          def test_local_cache_cleared_on_close
+            key = "super awesome key"
+            assert_nil LocalCacheRegistry.cache_for key
+            middleware = Middleware.new('<3', key).new(->(env) {
+              assert LocalCacheRegistry.cache_for(key), 'should have a cache'
+              [200, {}, []]
+            })
+            _, _, body = middleware.call({})
+            assert LocalCacheRegistry.cache_for(key), 'should still have a cache'
+            body.each { }
+            assert LocalCacheRegistry.cache_for(key), 'should still have a cache'
+            body.close
+            assert_nil LocalCacheRegistry.cache_for(key)
+          end
+
+          def test_local_cache_cleared_on_exception
+            key = "super awesome key"
+            assert_nil LocalCacheRegistry.cache_for key
+            middleware = Middleware.new('<3', key).new(->(env) {
+              assert LocalCacheRegistry.cache_for(key), 'should have a cache'
+              raise
+            })
+            assert_raises(RuntimeError) { middleware.call({}) }
+            assert_nil LocalCacheRegistry.cache_for(key)
+          end
+        end
+      end
+    end
+  end
+end
+
 class CacheKeyTest < ActiveSupport::TestCase
   def test_entry_legacy_optional_ivars
     legacy = Class.new(ActiveSupport::Cache::Entry) do
@@ -577,6 +613,7 @@ def test_middleware
       result = @cache.write('foo', 'bar')
       assert_equal 'bar', @cache.read('foo') # make sure 'foo' was written
       assert result
+      [200, {}, []]
     }
     app = @cache.middleware.new(app)
     app.call({})