Render It!: A Deep Dive into ActionView and Template Engines

Slides for Rails Pacific 2014 talk "Render It!: A Deep Dive into ActionView and Template Engines" http://railspacific.com/

1. A Deep Dive into ActionView and Template Engines Render It! Akira Matsuda
5. begin
6. Contents Part 1: Action View Part 2: Template Engines
7. Part 1: Action View
8. Action View The view layer of Ruby on Rails framework
9. Action View Rails <= 4.0: Part of Action Pack Rails 4.1: Extracted to a separate gem
10. Names Documented name: Action View Gem name: actionview Directory name: action_view Module name: ActionView
11. The gemspec
12. actionview.gemspec Gem::Specification.new do |s| ... s.add_dependency 'activesupport', version s.add_dependency 'builder', '~> 3.1' s.add_dependency 'erubis', '~> 2.7.0' s.add_dependency 'rails-html-sanitizer', '~> 1.0' s.add_dependency 'rails-dom-testing', '~> 1.0', '>= 1.0.2' s.add_development_dependency 'actionpack', version s.add_development_dependency 'activemodel', version end
13. actionview's dependencies actionview is not depending on rails
14. actionview.gemspec Gem::Specification.new do |s| ... s.add_dependency 'activesupport', version s.add_dependency 'builder', '~> 3.1' s.add_dependency 'erubis', '~> 2.7.0' s.add_dependency 'rails-html-sanitizer', '~> 1.0' s.add_dependency 'rails-dom-testing', '~> 1.0', '>= 1.0.2' s.add_development_dependency 'actionpack', version s.add_development_dependency 'activemodel', version end
15. s.add_development_dependency 'actionpack' Uses actionpack only for its testing Doesn't require actionpack in runtime
16. Why was ActionView extracted? Any usecase?
17. Why was ActionView extracted? Rails apps without ActionView Something more lightweight, maybe?
18. Why was ActionView extracted? Rails apps without ActionView Something more lightweight, maybe? Apps without rails / actionpack e.g. Sinatra You can use ActionView's rich helper methods View files could be rails compatible
19. Why was ActionView extracted? Rails apps without ActionView Apps without rails / actionpack
20. Rails apps without ActionView
21. Rails apps without ActionView Let's make sure if this is possible.
22. rails --help Options: -r, [--ruby=PATH] # Path to the Ruby binary of your choice # Default: /Users/a_matsuda/.rbenv/versions/2.1.3/bin/ruby -m, [--template=TEMPLATE] # Path to some application template (can be a filesystem path or URL) [--skip-gemfile], [--no-skip-gemfile] # Don't create a Gemfile -B, [--skip-bundle], [--no-skip-bundle] # Don't run bundle install -G, [--skip-git], [--no-skip-git] # Skip .gitignore file [--skip-keeps], [--no-skip-keeps] # Skip source control .keep files -O, [--skip-active-record], [--no-skip-active-record] # Skip Active Record files -V, [--skip-action-view], [--no-skip-action-view] # Skip Action View files -S, [--skip-sprockets], [--no-skip-sprockets] # Skip Sprockets files [--skip-spring], [--no-skip-spring] # Don't install Spring application preloader -d, [--database=DATABASE] # Preconfigure for selected database (options: mysql/oracle/postgresql/ sqlite3/frontbase/ibm_db/sqlserver/jdbcmysql/jdbcsqlite3/jdbcpostgresql/jdbc) # Default: sqlite3 -j, [--javascript=JAVASCRIPT] # Preconfigure for selected JavaScript library # Default: jquery -J, [--skip-javascript], [--no-skip-javascript] # Skip JavaScript files [--dev], [--no-dev] # Setup the application with Gemfile pointing to your Rails checkout [--edge], [--no-edge] # Setup the application with Gemfile pointing to Rails repository -T, [--skip-test-unit], [--no-skip-test-unit] # Skip Test::Unit files [--rc=RC] # Path to file containing extra configuration options for rails command [--no-rc], [--no-no-rc] # Skip loading of extra configuration options from .railsrc file
23. OMG there it is! Options: -r, [--ruby=PATH] # Path to the Ruby binary of your choice # Default: /Users/a_matsuda/.rbenv/versions/2.1.3/bin/ruby -m, [--template=TEMPLATE] # Path to some application template (can be a filesystem path or URL) [--skip-gemfile], [--no-skip-gemfile] # Don't create a Gemfile -B, [--skip-bundle], [--no-skip-bundle] # Don't run bundle install -G, [--skip-git], [--no-skip-git] # Skip .gitignore file [--skip-keeps], [--no-skip-keeps] # Skip source control .keep files -O, [--skip-active-record], [--no-skip-active-record] # Skip Active Record files -V, [--skip-action-view], [--no-skip-action-view] # Skip Action View files -S, [--skip-sprockets], [--no-skip-sprockets] # Skip Sprockets files [--skip-spring], [--no-skip-spring] # Don't install Spring application preloader -d, [--database=DATABASE] # Preconfigure for selected database (options: mysql/oracle/postgresql/ sqlite3/frontbase/ibm_db/sqlserver/jdbcmysql/jdbcsqlite3/jdbcpostgresql/jdbc) # Default: sqlite3 -j, [--javascript=JAVASCRIPT] # Preconfigure for selected JavaScript library # Default: jquery -J, [--skip-javascript], [--no-skip-javascript] # Skip JavaScript files [--dev], [--no-dev] # Setup the application with Gemfile pointing to your Rails checkout [--edge], [--no-edge] # Setup the application with Gemfile pointing to Rails repository -T, [--skip-test-unit], [--no-skip-test-unit] # Skip Test::Unit files [--rc=RC] # Path to file containing extra configuration options for rails command [--no-rc], [--no-no-rc] # Skip loading of extra configuration options from .railsrc file
24. % rails new no_actionview -V
25. config/application.rb # Pick the frameworks you want: require "active_model/railtie" require "active_record/railtie" require "action_controller/railtie" require "action_mailer/railtie" # require "action_view/railtie" require "sprockets/railtie" require "rails/test_unit/railtie"
26. OMG my app is actionview free! But how does it render?
27. Let's generate something % rails g scaffold user name % rake db:migrate % rails s % open http://localhost:3000/users
28. Apparently it renders the view...
29. config/application.rb # Pick the frameworks you want: require "active_model/railtie" require "active_record/railtie" require "action_controller/railtie" require "action_mailer/railtie" # require "action_view/railtie" require "sprockets/railtie" require "rails/test_unit/railtie"
30. actionpack/lib/action_controller/ railtie.rb require "rails" require "action_controller" require "action_dispatch/railtie" require "abstract_controller/railties/ routes_helpers" require "action_controller/railties/helpers" require "action_view/railtie"
31. WTF
32. This should be a bug. Let's just remove this line. require "action_dispatch/railtie" require "abstract_controller/railties/routes_helpers" require "action_controller/railties/helpers" -require "action_view/railtie" module ActionController class Railtie < Rails::Railtie #:nodoc:
33. That's it! Is everything OK?
34. Unfortunately, no.
35. Because these gems depend on actionview in their gemspecs actionpack actionmailer sprockets-rails (rails depends on it)
36. And they touch ActionView code casually. For example,
37. actionpack/lib/abstract_controller/ rendering.rb module AbstractController module Rendering extend ActiveSupport::Concern include ActionView::ViewPaths ennd
38. sprockets-rails/sprockets/rails/ helper.rb require 'action_view' require 'sprockets' require 'active_support/core_ext/class/attribute' module Sprockets module Rails module Helper ... include ActionView::Helpers::AssetUrlHelper include ActionView::Helpers::AssetTagHelper ...
39. You can not skip loading actionview --skip-action-view option was totally meaningless
40. So, I wrote an issue 3.days.ago
42. Jeremy said, :+1: to remove `skip-action-view`
43. So, the option was removed --skip-action-view option was only available in Rails 4.1 Will be removed since Rails 4.2
44. Why was ActionView extracted? Rails apps without ActionView Apps without rails / actionpack
45. Apps without rails / actionpack
46. Let's try creating a minimum ActionView app A command line app that renders a template to STDOUT
47. render :text Let's start off with a very simple case
48. How can I render? Maybe there's a method named "render" inside actionview?
49. % git grep "def render" % git grep "def render" actionview/lib dependency_tracker.rb: def render_dependencies helpers/rendering_helper.rb: def render(options = {}, locals = {}, &block) helpers/tags/base.rb: def render helpers/tags/check_box.rb: def render helpers/tags/collection_check_boxes.rb: def render(&block) helpers/tags/collection_check_boxes.rb: def render_component(builder) helpers/tags/collection_helpers.rb: def render_collection #:nodoc: helpers/tags/collection_radio_buttons.rb: def render(&block) helpers/tags/collection_radio_buttons.rb: def render_component(builder) helpers/tags/collection_select.rb: def render helpers/tags/color_field.rb: def render helpers/tags/date_select.rb: def render helpers/tags/datetime_field.rb: def render helpers/tags/grouped_collection_select.rb: def render helpers/tags/label.rb: def render(&block) helpers/tags/label.rb: def render_component(builder) helpers/tags/number_field.rb: def render helpers/tags/password_field.rb: def render helpers/tags/radio_button.rb: def render helpers/tags/search_field.rb: def render helpers/tags/select.rb: def render helpers/tags/text_area.rb: def render helpers/tags/text_field.rb: def render helpers/tags/time_zone_select.rb: def render log_subscriber.rb: def render_template(event) renderer/abstract_renderer.rb: def render renderer/partial_renderer.rb: def render(context, options, block) renderer/partial_renderer.rb: def render_collection renderer/partial_renderer.rb: def render_partial renderer/renderer.rb: def render(context, options) renderer/renderer.rb: def render_body(context, options) renderer/renderer.rb: def render_template(context, options) #:nodoc: renderer/renderer.rb: def render_partial(context, options, &block) #:nodoc: renderer/streaming_template_renderer.rb: def render_template(template, layout_name = nil, locals = {}) #:nodoc: renderer/template_renderer.rb: def render(context, options) renderer/template_renderer.rb: def render_template(template, layout_name = nil, locals = nil) #:nodoc: renderer/template_renderer.rb: def render_with_layout(path, locals) #:nodoc: rendering.rb: def render_to_body(options = {}) rendering.rb: def rendered_format template.rb: def render(view, locals, buffer=nil, &block) template/html.rb: def render(*args) template/text.rb: def render(*args) test_case.rb: def render(options = {}, local_assigns = {}, &block) test_case.rb: def rendered_views test_case.rb: def rendered_views test_case.rb: def render(options = {}, local_assigns = {})
50. % git grep "def render" 46 render-ish methods inside actionview!
51. Helpers::Tags and TestCase % git grep "def render" actionview/lib dependency_tracker.rb: def render_dependencies helpers/rendering_helper.rb: def render(options = {}, locals = {}, &block) helpers/tags/base.rb: def render helpers/tags/check_box.rb: def render helpers/tags/collection_check_boxes.rb: def render(&block) helpers/tags/collection_check_boxes.rb: def render_component(builder) helpers/tags/collection_helpers.rb: def render_collection #:nodoc: helpers/tags/collection_radio_buttons.rb: def render(&block) helpers/tags/collection_radio_buttons.rb: def render_component(builder) helpers/tags/collection_select.rb: def render helpers/tags/color_field.rb: def render helpers/tags/date_select.rb: def render helpers/tags/datetime_field.rb: def render helpers/tags/grouped_collection_select.rb: def render helpers/tags/label.rb: def render(&block) helpers/tags/label.rb: def render_component(builder) helpers/tags/number_field.rb: def render helpers/tags/password_field.rb: def render helpers/tags/radio_button.rb: def render helpers/tags/search_field.rb: def render helpers/tags/select.rb: def render helpers/tags/text_area.rb: def render helpers/tags/text_field.rb: def render helpers/tags/time_zone_select.rb: def render log_subscriber.rb: def render_template(event) renderer/abstract_renderer.rb: def render renderer/partial_renderer.rb: def render(context, options, block) renderer/partial_renderer.rb: def render_collection renderer/partial_renderer.rb: def render_partial renderer/renderer.rb: def render(context, options) renderer/renderer.rb: def render_body(context, options) renderer/renderer.rb: def render_template(context, options) #:nodoc: renderer/renderer.rb: def render_partial(context, options, &block) #:nodoc: renderer/streaming_template_renderer.rb: def render_template(template, layout_name = nil, locals = {}) #:nodoc: renderer/template_renderer.rb: def render(context, options) renderer/template_renderer.rb: def render_template(template, layout_name = nil, locals = nil) #:nodoc: renderer/template_renderer.rb: def render_with_layout(path, locals) #:nodoc: rendering.rb: def render_to_body(options = {}) rendering.rb: def rendered_format template.rb: def render(view, locals, buffer=nil, &block) template/html.rb: def render(*args) template/text.rb: def render(*args) test_case.rb: def render(options = {}, local_assigns = {}, &block) test_case.rb: def rendered_views test_case.rb: def rendered_views test_case.rb: def render(options = {}, local_assigns = {})
52. Excluding Helpers::Tags and TestCase % git grep "def render" actionview/lib | grep -v "^helpers\/tags\/" | grep -v "^test_case\.rb" dependency_tracker.rb: def render_dependencies helpers/rendering_helper.rb: def render(options = {}, locals = {}, &block) log_subscriber.rb: def render_template(event) renderer/abstract_renderer.rb: def render renderer/partial_renderer.rb: def render(context, options, block) renderer/partial_renderer.rb: def render_collection renderer/partial_renderer.rb: def render_partial renderer/renderer.rb: def render(context, options) renderer/renderer.rb: def render_body(context, options) renderer/renderer.rb: def render_template(context, options) #:nodoc: renderer/renderer.rb: def render_partial(context, options, &block) #:nodoc: renderer/streaming_template_renderer.rb: def render_template(template, layout_name = nil, locals = {}) #:nodoc: renderer/template_renderer.rb: def render(context, options) renderer/template_renderer.rb: def render_template(template, layout_name = nil, locals = nil) #:nodoc: renderer/template_renderer.rb: def render_with_layout(path, locals) #:nodoc: rendering.rb: def render_to_body(options = {}) rendering.rb: def rendered_format template.rb: def render(view, locals, buffer=nil, &block) template/html.rb: def render(*args) template/text.rb: def render(*args)
53. Excluding Helpers::Tags and TestCase Still 20 render methods... No matter which one, view should respond_to `render`
54. Maybe something like this should work?
55. actionview_app/Gemfile source 'https://rubygems.org/' gem 'actionview', require: 'action_view'
56. app.rb - render :text Bundler.require puts ActionView::Base.new.render(text: 'hello')
57. app.rb - render :text Bundler.require puts ActionView::Base.new.render(text: 'hello') #=> hello
58. OMG it worked!
59. render :inline Rendering an inline ERB string
60. Rendering an inline ERB template Bundler.require puts ActionView::Base.new.render(inline: '<%= "hello" %>') #=> hello
61. render :file Finding a template from the filesystem
62. hello.txt % echo hello > hello.txt
63. app.rb - render :file Bundler.require puts ActionView::Base.new.render(file: 'hello.txt')
64. Error! % bundle ex ruby app.rb action_view/lookup_context.rb:69:in `get': uninitialized constant ActionView::LookupContext::DetailsKey::Mime (NameError) from action_view/lookup_context.rb:90:in `details_key' from action_view/lookup_context.rb:158:in `detail_args_for' from action_view/lookup_context.rb:152:in `args_for_lookup' from action_view/lookup_context.rb:121:in `find' from action_view/renderer/abstract_renderer.rb:18:in `find_template' from action_view/renderer/template_renderer.rb:32:in `block in determine_template' from action_view/lookup_context.rb:143:in `with_fallbacks' from action_view/renderer/abstract_renderer.rb:18:in `with_fallbacks' from action_view/renderer/template_renderer.rb:32:in `determine_template' from action_view/renderer/template_renderer.rb:8:in `render' from action_view/renderer/renderer.rb:42:in `render_template' from action_view/renderer/renderer.rb:23:in `render' from action_view/helpers/rendering_helper.rb:32:in `render' from app.rb:2:in `<main>'
65. What is Mime? ::Mime is a module defined in actionpack/lib/action_dispatch/http/mime_type.rb
66. s.add_development_dependency 'actionpack' Uses actionpack only for testing Doesn't require actionpack in runtime I'm sorry I told you a lie! actionview still depends on actionpack in runtime!
67. So, I wrote an issue 3.days.ago
69. Jeremy said, :+1: it should have a runtime dependency. It's still closely coupled with Action Pack.
70. Apps without rails / actionpack It turned out this was impossible At least, I'm sure nobody has tried this before
71. Why was ActionView extracted? Rails apps without ActionView Apps without rails / actionpack
72. Why was ActionView extracted?
73. Why was ActionView extracted? ¯\_(π)_/¯
74. ProTip: How to find Rails bugs Try something weird on Rails like this
75. Workaround % cp AD/http/mime_type.rb .
76. app.rb - Workaround Bundler.require # copied from AD/http/mime_type.rb (and cut the last line) require_relative 'mime_type' puts ActionView::Base.new.render(file: 'hello.txt') #=> hello
77. render :template
78. hello.html.erb % echo "<%= 'hello, erb!' %>" > hello.html.erb
79. app.rb - render :template Bundler.require require_relative 'mime_type' puts ActionView::Base.new.render(template: 'hello.html.erb')
80. Error! % bundle ex ruby app.rb action_view/path_set.rb:46:in `find': Missing template /hello.html.erb with {:locale=>[:en], :formats=>[:html, :text, :js, :css, :xml, :json], :variants=>[], :handlers=>[:erb, :builder, :raw, :ruby]}. Searched in: (ActionView::MissingTemplate) from action_view/lookup_context.rb:121:in `find' from action_view/renderer/abstract_renderer.rb:18:in `find_template' from action_view/renderer/template_renderer.rb:40:in `determine_template' from action_view/renderer/template_renderer.rb:8:in `render' from action_view/renderer/renderer.rb:42:in `render_template' from action_view/renderer/renderer.rb:23:in `render' from action_view/helpers/rendering_helper.rb:32:in `render' from app.rb:13:in `<main>'
81. app.rb - render :template Bundler.require require_relative 'mime_type' # need to give a view_path puts ActionView::Base.new('.').render(template: 'hello.html.erb') #=> hello, erb!
82. render template: 'hello' No need to specify ".html.erb" actionview would find a template having suitable format and handler (and locale and variants)
83. app.rb - render :template Bundler.require require_relative 'mime_type' # no need to specify ".html.erb" puts ActionView::Base.new('.').render(template: 'hello') #=> hello, erb!
84. What does render :template do? Time for code reading!
85. How does the actual Rails controller render? % rails new someapp % cd someapp % rails g controller welcome index % echo "<% puts caller %>" >> app/views/ welcome/index.html.erb % rails s % open http://localhost:3000/welcome/index
86. The callers actionview/lib/action_view/template.rb:145:in `block in render' activesupport/lib/active_support/notifications.rb:166:in `instrument' actionview/lib/action_view/template.rb:329:in `instrument' actionview/lib/action_view/template.rb:143:in `render' actionview/lib/action_view/renderer/template_renderer.rb:54:in `block (2 levels) in render_template' actionview/lib/action_view/renderer/abstract_renderer.rb:39:in `block in instrument' activesupport/lib/active_support/notifications.rb:164:in `block in instrument' activesupport/lib/active_support/notifications/instrumenter.rb:20:in `instrument' activesupport/lib/active_support/notifications.rb:164:in `instrument' actionview/lib/action_view/renderer/abstract_renderer.rb:39:in `instrument' actionview/lib/action_view/renderer/template_renderer.rb:53:in `block in render_template' actionview/lib/action_view/renderer/template_renderer.rb:61:in `render_with_layout' actionview/lib/action_view/renderer/template_renderer.rb:52:in `render_template' actionview/lib/action_view/renderer/template_renderer.rb:14:in `render' actionview/lib/action_view/renderer/renderer.rb:42:in `render_template' actionview/lib/action_view/renderer/renderer.rb:23:in `render' actionview/lib/action_view/rendering.rb:100:in `_render_template' actionpack/lib/action_controller/metal/streaming.rb:217:in `_render_template' actionview/lib/action_view/rendering.rb:83:in `render_to_body' actionpack/lib/action_controller/metal/rendering.rb:32:in `render_to_body' actionpack/lib/action_controller/metal/renderers.rb:37:in `render_to_body' actionpack/lib/abstract_controller/rendering.rb:25:in `render'
87. rendering.rb module ActionView module Rendering def _render_template(options) ... view_renderer.render(view_context, options) ennnd
88. _render_template It calls `view_renderer`'s `render` method that takes a `view_context`
89. What is `view_context`? module ActionView module Rendering def view_context view_context_class.new(view_renderer, view_assigns, self) end def view_context_class @_view_context_class ||= self.class.view_context_class ennnd
90. What is `view_context`? module ActionView module Rendering module ClassMethods def view_context_class @view_context_class ||= begin include_path_helpers = supports_path? routes = respond_to?(:_routes) && _routes helpers = respond_to?(:_helpers) && _helpers Class.new(ActionView::Base) do if routes include routes.url_helpers(include_path_helpers) include routes.mounted_helpers end if helpers include helpers ennnnnnnd
91. `view_context` is not a direct instance of ActionView::Base class an instance of an anonymous child class of ActionView::Base
92. What is `view_renderer`? module ActionView class Base attr_accessor :view_renderer def initialize(context = nil, assigns = {}, controller = nil, formats = nil) ... @view_renderer = ActionView::Renderer.new(lookup_context) ... ennnd
93. `view_renderer` is an instance of ActionView::Renderer
94. Back to rendering.rb module ActionView module Rendering def _render_template(options) ... view_renderer.render(view_context, options) ennnd
95. render,
96. renderer/renderer.rb module ActionView class Renderer def render(context, options) if options.key?(:partial) ... else render_template(context, options) ennnnd
97. render_template after render,
98. renderer/renderer.rb module ActionView class Renderer def render_template(context, options) ... TemplateRenderer.new(@lookup_context).render(context, options) ennnd
99. Another render after render_template after render,
100. renderer/template_renderer.rb module ActionView class TemplateRenderer < AbstractRenderer def render(context, options) @view = context ... template = determine_template(options) ... render_template(template, options[:layout], options[:locals]) ennnd
101. Then another render_template after another render after render_template after render. This render method determines a template, then renders it
102. renderer/template_renderer.rb module ActionView class TemplateRenderer < AbstractRenderer def determine_template(options) ... elsif options.key?(:text) Template::Text.new(options[:text], formats.first) ... elsif options.key?(:inline) handler = Template.handler_for_extension(options[:type] || "erb") Template.new(options[:inline], "inline template", handler, :locals => keys) elsif options.key?(:template) ... find_template(options[:template], options[:prefixes], false, keys, @details) ennnnnd
103. render :text
104. template/text.rb module ActionView class Template class Text def initialize(string, type = nil) @string = string.to_s ... end def to_str @string end def render(*args) to_str ennnnd
105. render :template
106. find_template Very very long journey LookupContext#find => PathSet#find => Resolver#find_all Finally finds a template Templates found are cached
107. template/resolver.rb handler, format, variant = extract_handler_and_format_and_variant(template, formats) contents = File.binread(template) Template.new(contents, File.expand_path(template), handler, :virtual_path => path.virtual, :format => format, :variant => variant, :updated_at => mtime(template) )
108. Template resolution Read the content from the file Create a handler instance Return an instance of Template that has the content and the handler
109. Handler Template Engines' interface handler_for_extension('erb') #=> ActionView::Template::Handlers::Erubis
110. renderer/template_renderer.rb module ActionView class TemplateRenderer < AbstractRenderer def render_template(template, layout_name = nil, locals = nil) ... template.render(view, locals) { |*name| view._layout_for(*name) } end
111. A template can render itself
112. template.rb module ActionView class Template def render(view, locals, buffer=nil, &block) ... compile!(view) view.send(method_name, locals, buffer, &block) ... ennnd
113. Template#render It compiles the view And executes something on the view object
114. template.rb module ActionView class Template def compile!(view) return if @compiled ... mod = view.singleton_class ... compile(mod) ... ennnd
115. compile! compile is executed only once
116. template.rb module ActionView class Template def compile(mod) ... method_name = self.method_name code = @handler.call(self) ... source = <<-end_src def #{method_name}(local_assigns, output_buffer) _old_virtual_path, @virtual_path = @virtual_path, #{@virtual_path.inspect};_old_output_buffer = @output_buffer;#{locals_code};#{code} ensure @virtual_path, @output_buffer = _old_virtual_path, _old_output_buffer end end_src ... mod.module_eval(source, identifier, 0) ... ennnd
117. compile @handler.call(template) returns a Ruby code The code is defined on the view context object as a Ruby method
118. template.rb module ActionView class Template def render(view, locals, buffer=nil, &block) ... compile!(view) view.send(method_name, locals, buffer, &block) ... ennnd
119. Back to `render` Then the defined method is called Template rendering is not `eval` but a method execution
120. Template Handler API A template handler has to respond_to #call that takes a Template instance #call returns a compiled HTML String
121. app.rb - subclassing ActionView::Base Bundler.require require_relative 'mime_type' Class.new(ActionView::Base).new('.').render(template: 'hello')
122. app.rb - confirming that a method was added Bundler.require require_relative 'mime_type' view = Class.new(ActionView::Base).new('.'). methods = view.public_methods view.render(template: 'hello') p view.public_methods - methods #=> [:___sers_a_matsuda_tmp_actionview_test_hello_html_erb___149 3524731793660833_70284245975760]
123. Part 2: Template Engines
124. Handler#call Let's take a look at actual implementations
125. Template Engines ERB Haml Slim
126. ERB
127. ERB ERB handler is bundled in actionview by default
128. template/handlers/erb.rb module ActionView class Template module Handlers class ERB class_attribute :erb_implementation self.erb_implementation = Erubis def call(template) ... self.class.erb_implementation.new( erb, :escape => (self.class.escape_whitelist.include? template.type), :trim => (self.class.erb_trim_mode == "-") ).src end
129. self.erb_implementation = Erubis Erubis is an ERB compatible eRuby library Looks as if erb_implementation is configurable
130. self.erb_implementation = ERB (?) But if you set this to `ERB` the actionview tests will never pass. Here's another unknown "meaningless option". Seki-san and I once tried to fix this before Ruby 2.0 release, but we failed... Weird.
131. ERB.new(erb).src % ruby -rerb -e "puts ERB.new('<%= 1 + 1 %>').src" #coding:UTF-8 _erbout = ''; _erbout.concat(( 1 + 1 ).to_s); _erbout.force_encoding(__ENCODING__)
132. ERB.new(erb).src It gets an ERB template string and returns a ruby code that generates the result HTML
133. Haml
134. Gemfile source 'https://rubygems.org/' gem 'actionview', require: 'action_view' gem 'haml'
135. hello.html.haml % echo "= 'hello, haml'" > hello.html.haml
136. app.rb - rendering haml Bundler.require require_relative 'mime_type' require 'haml/template' view = Class.new(ActionView::Base).new('.') puts view.render(template: 'hello', handlers: 'haml')
137. app.rb - rendering haml with weird monkey-patches Bundler.require require_relative 'mime_type' module ActionPack module VERSION MAJOR = 4 end end module Rails def self.env ActiveSupport::StringInquirer.new('production') end end require 'haml/template' view = Class.new(ActionView::Base).new('.') puts view.render(template: 'hello', handlers: 'haml')
138. Slim
139. Gemfile source 'https://rubygems.org/' gem 'actionview', require: 'action_view' gem 'haml' gem 'slim', require: false
140. hello.html.slim % echo "= 'hello, slim'" > hello.html.slim
141. app.rb - rendering slim with weird monkey-patches Bundler.require require_relative 'mime_type' module ActionPack module VERSION MAJOR = 4 end end module Rails def self.env ActiveSupport::StringInquirer.new('production') end end require 'slim' view = Class.new(ActionView::Base).new('.') puts view.render(template: 'hello', handlers: 'slim')
142. Template Engines Which engine is fast?
143. Benchmark!
144. Gemfile source 'https://rubygems.org/' gem 'actionview', path: '~/src/rails/actionview', require: 'action_view' gem 'haml' gem 'slim', require: false gem 'benchmark-ips'
145. Benchmark! Bundler.require require_relative 'mime_type' module ActionPack module VERSION MAJOR = 4 end end module Rails def self.env ActiveSupport::StringInquirer.new('production') end end require 'haml/template' require 'slim' view = Class.new(ActionView::Base).new('.') # discard the first execution that contains template lookup and compilation view.render(template: 'hello', handlers: 'erb') view.render(template: 'hello', handlers: 'haml') view.render(template: 'hello', handlers: 'slim') Benchmark.ips do |x| x.report('erb') { view.render(template: 'hello', handlers: 'erb') } x.report('haml') { view.render(template: 'hello', handlers: 'haml') } x.report('slim') { view.render(template: 'hello', handlers: 'slim') } end
146. Benchmark results % bundle ex ruby app.rb Calculating ------------------------------------- erb 1839 i/100ms haml 1440 i/100ms slim 1920 i/100ms ------------------------------------------------- erb 19261.7 (±4.2%) i/s - 97467 in 5.069805s haml 14662.8 (±5.0%) i/s - 73440 in 5.022658s slim 19673.9 (±3.6%) i/s - 99840 in 5.081665s
147. Haml is so slow!
150. So, I tried to improve the speed a little bit
151. Results % bx ruby app.rb Calculating ------------------------------------- erb 1824 i/100ms haml(gem) 1440 i/100ms haml(fork) 1553 i/100ms slim 1875 i/100ms ------------------------------------------------- erb 19614.9 (±3.4%) i/s - 98496 in 5.027551s haml(gem) 14662.8 (±5.0%) i/s - 73440 in 5.022658s haml(fork) 16193.5 (±4.2%) i/s - 82309 in 5.092455s slim 20193.5 (±3.5%) i/s - 101250 in 5.020527s
152. end