Make digest cache work in development.

Avoid computing the same fragment digest many times when looping over templates.

The cache is cleared on every request so template changes are still picked up.

actionview/lib/action_view/digestor.rb

@@ -8,6 +8,13 @@ class Digestor
     @@cache          = ThreadSafe::Cache.new
     @@digest_monitor = Monitor.new
 
+    class PerRequestDigestCacheExpiry < Struct.new(:app) # :nodoc:
+      def call(env)
+        ActionView::Digestor.cache.clear
+        app.call(env)
+      end
+    end
+
     class << self
       # Supported options:
       #
@@ -41,10 +48,7 @@ def compute_and_store_digest(cache_key, options) # called under @@digest_monitor
             Digestor
           end
 
-          digest = klass.new(options).digest
-          # Store the actual digest if config.cache_template_loading is true
-          @@cache[cache_key] = stored_digest = digest if ActionView::Resolver.caching?
-          digest
+          @@cache[cache_key] = stored_digest = klass.new(options).digest
         ensure
           # something went wrong or ActionView::Resolver.caching? is false, make sure not to corrupt the @@cache
           @@cache.delete_pair(cache_key, false) if pre_stored && !stored_digest

actionview/lib/action_view/railtie.rb

@@ -42,6 +42,14 @@ class Railtie < Rails::Railtie # :nodoc:
       end
     end
 
+    initializer "action_view.per_request_digest_cache" do |app|
+      ActiveSupport.on_load(:action_view) do
+        if app.config.consider_all_requests_local
+          app.middleware.use ActionView::Digestor::PerRequestDigestCacheExpiry
+        end
+      end
+    end
+
     initializer "action_view.setup_action_pack" do |app|
       ActiveSupport.on_load(:action_controller) do
         ActionView::RoutingUrlFor.include(ActionDispatch::Routing::UrlFor)

actionview/test/template/digestor_test.rb

@@ -239,16 +239,6 @@ def test_dependencies_via_options_results_in_different_digest
     assert_not_equal digest_phone, digest_fridge_phone
   end
 
-  def test_cache_template_loading
-    resolver_before = ActionView::Resolver.caching
-    ActionView::Resolver.caching = false
-    assert_digest_difference("messages/edit", true) do
-      change_template("comments/_comment")
-    end
-  ensure
-    ActionView::Resolver.caching = resolver_before
-  end
-
   def test_digest_cache_cleanup_with_recursion
     first_digest = digest("level/_recursion")
     second_digest = digest("level/_recursion")

railties/test/application/per_request_digest_cache_test.rb

+require 'isolation/abstract_unit'
+require 'rack/test'
+require 'minitest/mock'
+
+require 'action_view'
+require 'active_support/testing/method_call_assertions'
+
+class PerRequestDigestCacheTest < ActiveSupport::TestCase
+  include ActiveSupport::Testing::Isolation
+  include ActiveSupport::Testing::MethodCallAssertions
+  include Rack::Test::Methods
+
+  setup do
+    build_app
+    add_to_config 'config.consider_all_requests_local = true'
+
+    app_file 'app/models/customer.rb', <<-RUBY
+      class Customer < Struct.new(:name, :id)
+        extend ActiveModel::Naming
+        include ActiveModel::Conversion
+      end
+    RUBY
+
+    app_file 'config/routes.rb', <<-RUBY
+      Rails.application.routes.draw do
+        resources :customers, only: :index
+      end
+    RUBY
+
+    app_file 'app/controllers/customers_controller.rb', <<-RUBY
+      class CustomersController < ApplicationController
+        def index
+          render [ Customer.new('david', 1), Customer.new('dingus', 2) ]
+        end
+      end
+    RUBY
+
+    app_file 'app/views/customers/_customer.html.erb', <<-RUBY
+      <% cache customer do %>
+        <%= customer.name %>
+      <% end %>
+    RUBY
+
+    require "#{app_path}/config/environment"
+  end
+
+  teardown :teardown_app
+
+  test "digests are reused when rendering the same template twice" do
+    get '/customers'
+    assert_equal 200, last_response.status
+
+    assert_equal [ '8ba099b7749542fe765ff34a6824d548' ], ActionView::Digestor.cache.values
+    assert_equal %w(david dingus), last_response.body.split.map(&:strip)
+  end
+
+  test "template digests are cleared before a request" do
+    assert_called(ActionView::Digestor.cache, :clear) do
+      get '/customers'
+      assert_equal 200, last_response.status
+    end
+  end
+end