Add the ability to precompile error pages on asset precompile

.gitignore

@@ -22,3 +22,4 @@ tmp
 *.a
 mkmf.log
 *.log
+test/fake_app/public/*.html

Appraisals

@@ -44,9 +44,9 @@ appraise "rails_70" do
 end
 
 appraise "rails_71" do
-  gem "activesupport", "~> 7.1.0.beta1"
-  gem "actionpack", "~> 7.1.0.beta1"
-  gem "railties", "~> 7.1.0.beta1"
+  gem "activesupport", "~> 7.1.0.rc2"
+  gem "actionpack", "~> 7.1.0.rc2"
+  gem "railties", "~> 7.1.0.rc2"
 end
 
 appraise "rails_edge" do

README.md

@@ -87,6 +87,35 @@ It will generate your own custom exceptions app. You can use whatever techniques
 
 **Heavily customizing the exceptions app is strongly discouraged as there would be no guard against bugs that occur in the exceptions app.**
 
+## Static Error Page Precompilation
+
+Generating error pages dynamically can be risky at times, but it isn't always necessary, especially when the error page doesn't rely on dynamic data such as authentication information to render the entire page. What's more crucial when constructing an error page is ensuring the use of the same assets as the main application and static pages. In such cases, error pages could be generated during the asset pre-completion phase, rather than at runtime.
+
+As of version 3.1.0, Rambulance provides a way to precompile error pages at the time of asset precomplication.
+
+### How to Use the Static Error Page Precomplation Feature
+
+TBD
+
+```ruby
+# config/initializers/rambulance.rb
+config.static_error_pages = Rails.env.production?
+```
+
+### FAQ & Troubleshooting
+
+#### What are the main differences between the dynamic mode and static mode?
+
+TBD
+
+#### I'm using `devise` and can't precompile error pages
+
+If you are using Devise, then an error `Devise could not find the 'Warden::Proxy' instance on your request environment` may occur, as it monkey-patches the `ActionController::Base` class. The code below illustrates how the proxy object could be fulfilled manually:
+
+```ruby
+TBD
+```
+
 ## Testing
 
 Rambulance ships with a test helper that allows you to test an error page generated by Rails. All you have to do is to `include Rambulance::TestHelper` and you will be able to use the `with_exceptions_app` DSDL:

Rakefile

@@ -14,7 +14,12 @@ namespace :test do
   task :custom do
     sh "rake test:default CUSTOM_EXCEPTIONS_APP=1"
   end
+
+  desc "Run tests for the static page mode"
+  task :static_pages do
+    sh "TEST=test/requests/static_error_pages_test.rb STATIC_ERROR_PAGES=1 rake test:default"
+  end
 end
 
-task(:test).enhance %w(test:default test:custom)
+task(:test).enhance %w(test:default test:custom test:static_pages)
 task default: :test

gemfiles/rails_71.gemfile

@@ -2,8 +2,8 @@
 
 source "https://rubygems.org"
 
-gem "activesupport", "~> 7.1.0.beta1"
-gem "actionpack", "~> 7.1.0.beta1"
-gem "railties", "~> 7.1.0.beta1"
+gem "activesupport", "~> 7.1.0.rc2"
+gem "actionpack", "~> 7.1.0.rc2"
+gem "railties", "~> 7.1.0.rc2"
 
 gemspec path: "../"

lib/rambulance/exceptions_app.rb

@@ -45,6 +45,19 @@ def self.local_prefixes
       [Rambulance.view_path]
     end
 
+    def self.precompile!(env: {}, assigns: {})
+      ERROR_HTTP_STATUSES.each do |http_status, status_in_words|
+        begin
+          html = renderer.new(env).render(status_in_words, assigns: assigns)
+          path = Rails.public_path.join("#{http_status}.html").to_s
+
+          File.write(path, html)
+        rescue ActionView::MissingTemplate
+          Rails.logger.info "Template for #{http_status}(#{status_in_words}) does not exist. Skiping..."
+        end
+      end
+    end
+
     ERROR_HTTP_STATUSES.values.each do |status_in_words|
       eval <<-ACTION, nil, __FILE__, __LINE__ + 1
         def #{status_in_words}

lib/rambulance/railtie.rb

@@ -1,36 +1,54 @@
 module Rambulance
   class Railtie < Rails::Railtie
+    config.rambulance = ActiveSupport::OrderedOptions.new
+    config.rambulance.static_error_pages = false
+
     initializer 'rambulance', after: :prepend_helpers_path do |app|
       ActiveSupport.on_load(:action_controller) do
         require "rambulance/exceptions_app"
       end
 
-      app.config.exceptions_app =
-        if app.config.respond_to?(:autoloader) && app.config.autoloader == :classic
-          ->(env) {
-            begin
-              ActiveSupport::Dependencies.load_missing_constant(Object, :ExceptionsApp)
-              ::ExceptionsApp.call(env)
-            rescue NameError
-              require "rambulance/exceptions_app" if !defined?(::Rambulance::ExceptionsApp)
-              ::Rambulance::ExceptionsApp.call(env)
-            end
-          }
-        else
-          ->(env) {
-            begin
-              ::ExceptionsApp.call(env)
-            rescue NameError
-              require "rambulance/exceptions_app" if !defined?(::Rambulance::ExceptionsApp)
-              ::Rambulance::ExceptionsApp.call(env)
-            end
-          }
-        end
+      exceptions_app = if app.config.respond_to?(:autoloader) && app.config.autoloader == :classic
+                         ->(env) {
+                           begin
+                             ActiveSupport::Dependencies.load_missing_constant(Object, :ExceptionsApp)
+                             ::ExceptionsApp.call(env)
+                           rescue NameError
+                             require "rambulance/exceptions_app" if !defined?(::Rambulance::ExceptionsApp)
+                             ::Rambulance::ExceptionsApp.call(env)
+                           end
+                         }
+                       else
+                         ->(env) {
+                           begin
+                             ::ExceptionsApp.call(env)
+                           rescue NameError
+                             require "rambulance/exceptions_app" if !defined?(::Rambulance::ExceptionsApp)
+                             ::Rambulance::ExceptionsApp.call(env)
+                           end
+                         }
+                       end
+
+      if !app.config.rambulance.static_error_pages
+        app.config.exceptions_app = exceptions_app
+      end
 
       ActiveSupport.on_load(:after_initialize) do
-        Rails.application.routes.append do
-          mount app.config.exceptions_app, at: '/rambulance'
-        end if Rails.env.development?
+        if Rails.env.development?
+          Rails.application.routes.append do
+            mount exceptions_app, at: '/rambulance'
+          end
+        end
+      end
+    end
+
+    rake_tasks do
+      require 'rambulance/exceptions_app'
+
+      if config.rambulance.static_error_pages && Rake::Task.task_defined?("assets:precompile")
+        Rake::Task["assets:precompile"].enhance do
+          Rake::Task["rambulance:precompile"].invoke
+        end
       end
     end
   end

lib/tasks/rambulance.rake

@@ -0,0 +1,12 @@
+namespace :rambulance do
+  desc "Precompiles static HTML files for each error status"
+  task precompile: :environment do
+    exceptions_app = begin
+                       ::ExceptionsApp
+                     rescue NameError
+                       Rambulance::ExceptionsApp
+                     end
+
+    exceptions_app.precompile!
+  end
+end

test/exceptions_app_test.rb

@@ -2,8 +2,25 @@
 
 class ExeptionsAppTest < ActionDispatch::IntegrationTest
   test 'returns 404 for unknown format for pages that do not exist' do
-    get '/does_not_exist', headers: { 'Accept' => '*/*'  }
+    get '/does_not_exist', headers: { 'Accept' => '*/*' }
 
     assert_equal 404, response.status
   end
+
+  if Rails.version >= '5.0.0'
+    test '#precompile! generates static HTML files for each error status' do
+      Dir[Rails.public_path.join("*.html")].each do |file|
+        File.delete(file)
+      end
+
+      Rambulance::ExceptionsApp.precompile!
+
+      assert File.exist?(Rails.public_path.join("400.html"))
+      assert File.exist?(Rails.public_path.join("403.html"))
+      assert File.exist?(Rails.public_path.join("404.html"))
+      assert File.exist?(Rails.public_path.join("406.html"))
+      assert File.exist?(Rails.public_path.join("500.html"))
+      assert_not File.exist?(Rails.public_path.join("401.html"))
+    end
+  end
 end

test/fake_app/rails_app.rb

@@ -1,4 +1,8 @@
 require 'jbuilder'
+require 'rake'
+
+# This task needs to be defined before the Rails application is loaded so Rambulance can override it.
+Rake::Task.define_task('assets:precompile')
 
 # config
 class TestApp < Rails::Application
@@ -10,12 +14,14 @@ class TestApp < Rails::Application
   config.root = File.dirname(__FILE__)
   config.autoload_paths += ["#{config.root}/lib"] if ENV["CUSTOM_EXCEPTIONS_APP"]
   config.hosts = "www.example.com"
+  config.rambulance.static_error_pages = !!ENV["STATIC_ERROR_PAGES"]
 
   if Rails::VERSION::STRING >= "5.2"
     config.action_controller.default_protect_from_forgery = true
   end
 end
 Rails.backtrace_cleaner.remove_silencers!
+Rails.application.load_tasks if ENV["STATIC_ERROR_PAGES"]
 Rails.application.initialize!
 
 # routes

test/requests/static_error_pages_test.rb

@@ -0,0 +1,27 @@
+require 'test_helper'
+
+class StaticErrorPagesTest < ActionController::TestCase
+  if ENV["STATIC_ERROR_PAGES"]
+    test 'the exceptions app is set to PublicExceptions' do
+      assert_nil Rails.application.config.exceptions_app
+    end
+
+    test 'the assets:precompile task is enhanced with rambulance:precompile' do
+      assert_not_empty Rake::Task['assets:precompile'].actions
+    end
+  else
+    test 'the exceptions app is set to PublicExceptions' do
+      assert_not_nil Rails.application.config.exceptions_app
+    end
+
+    test 'the assets:precompile task is not enhanced with rambulance:precompile' do
+      assert_empty Rake::Task['assets:precompile'].actions
+    end
+  end
+
+  test 'the exceptions app is mounted on /rambulance' do
+    route = Rails.application.routes.routes.find { |route| route.path.spec.to_s == '/rambulance' }
+
+    assert_not_nil route
+  end
+end