actionview/lib/action_view/layouts.rb
# frozen_string_literal: true
require "action_view/rendering"
require "active_support/core_ext/module/redefine_method"
module ActionView
# = Action View \Layouts
#
# Layouts reverse the common pattern of including shared headers and footers in many templates to isolate changes in
# repeated setups. The inclusion pattern has pages that look like this:
#
# <%= render "application/header" %>
# Hello World
# <%= render "application/footer" %>
#
# This approach is a decent way of keeping common structures isolated from the changing content, but it's verbose
# and if you ever want to change the structure of these two includes, you'll have to change all the templates.
#
# With layouts, you can flip it around and have the common structure know where to insert changing content. This means
# that the header and footer are only mentioned in one place, like this:
#
# // The header part of this layout
# <%= yield %>
# // The footer part of this layout
#
# And then you have content pages that look like this:
#
# hello world
#
# At rendering time, the content page is computed and then inserted in the layout, like this:
#
# // The header part of this layout
# hello world
# // The footer part of this layout
#
# == Accessing shared variables
#
# Layouts have access to variables specified in the content pages and vice versa. This allows you to have layouts with
# references that won't materialize before rendering time:
#
# <h1><%= @page_title %></h1>
# <%= yield %>
#
# ...and content pages that fulfill these references _at_ rendering time:
#
# <% @page_title = "Welcome" %>
# Off-world colonies offers you a chance to start a new life
#
# The result after rendering is:
#
# <h1>Welcome</h1>
# Off-world colonies offers you a chance to start a new life
#
# == Layout assignment
#
# You can either specify a layout declaratively (using the #layout class method) or give
# it the same name as your controller, and place it in <tt>app/views/layouts</tt>.
# If a subclass does not have a layout specified, it inherits its layout using normal Ruby inheritance.
#
# For instance, if you have PostsController and a template named <tt>app/views/layouts/posts.html.erb</tt>,
# that template will be used for all actions in PostsController and controllers inheriting
# from PostsController.
#
# If you use a module, for instance Weblog::PostsController, you will need a template named
# <tt>app/views/layouts/weblog/posts.html.erb</tt>.
#
# Since all your controllers inherit from ApplicationController, they will use
# <tt>app/views/layouts/application.html.erb</tt> if no other layout is specified
# or provided.
#
# == Inheritance Examples
#
# class BankController < ActionController::Base
# # bank.html.erb exists
#
# class ExchangeController < BankController
# # exchange.html.erb exists
#
# class CurrencyController < BankController
#
# class InformationController < BankController
# layout "information"
#
# class TellerController < InformationController
# # teller.html.erb exists
#
# class EmployeeController < InformationController
# # employee.html.erb exists
# layout nil
#
# class VaultController < BankController
# layout :access_level_layout
#
# class TillController < BankController
# layout false
#
# In these examples, we have three implicit lookup scenarios:
# * The +BankController+ uses the "bank" layout.
# * The +ExchangeController+ uses the "exchange" layout.
# * The +CurrencyController+ inherits the layout from BankController.
#
# However, when a layout is explicitly set, the explicitly set layout wins:
# * The +InformationController+ uses the "information" layout, explicitly set.
# * The +TellerController+ also uses the "information" layout, because the parent explicitly set it.
# * The +EmployeeController+ uses the "employee" layout, because it set the layout to +nil+, resetting the parent configuration.
# * The +VaultController+ chooses a layout dynamically by calling the <tt>access_level_layout</tt> method.
# * The +TillController+ does not use a layout at all.
#
# == Types of layouts
#
# Layouts are basically just regular templates, but the name of this template needs not be specified statically. Sometimes
# you want to alternate layouts depending on runtime information, such as whether someone is logged in or not. This can
# be done either by specifying a method reference as a symbol or using an inline method (as a proc).
#
# The method reference is the preferred approach to variable layouts and is used like this:
#
# class WeblogController < ActionController::Base
# layout :writers_and_readers
#
# def index
# # fetching posts
# end
#
# private
# def writers_and_readers
# logged_in? ? "writer_layout" : "reader_layout"
# end
# end
#
# Now when a new request for the index action is processed, the layout will vary depending on whether the person accessing
# is logged in or not.
#
# If you want to use an inline method, such as a proc, do something like this:
#
# class WeblogController < ActionController::Base
# layout proc { |controller| controller.logged_in? ? "writer_layout" : "reader_layout" }
# end
#
# If an argument isn't given to the proc, it's evaluated in the context of
# the current controller anyway.
#
# class WeblogController < ActionController::Base
# layout proc { logged_in? ? "writer_layout" : "reader_layout" }
# end
#
# Of course, the most common way of specifying a layout is still just as a plain template name:
#
# class WeblogController < ActionController::Base
# layout "weblog_standard"
# end
#
# The template will be looked always in <tt>app/views/layouts/</tt> folder. But you can point
# <tt>layouts</tt> folder direct also. <tt>layout "layouts/demo"</tt> is the same as <tt>layout "demo"</tt>.
#
# Setting the layout to +nil+ forces it to be looked up in the filesystem and falls back to the parent behavior if none exists.
# Setting it to +nil+ is useful to re-enable template lookup overriding a previous configuration set in the parent:
#
# class ApplicationController < ActionController::Base
# layout "application"
# end
#
# class PostsController < ApplicationController
# # Will use "application" layout
# end
#
# class CommentsController < ApplicationController
# # Will search for "comments" layout and fall back to "application" layout
# layout nil
# end
#
# == Conditional layouts
#
# If you have a layout that by default is applied to all the actions of a controller, you still have the option of rendering
# a given action or set of actions without a layout, or restricting a layout to only a single action or a set of actions. The
# <tt>:only</tt> and <tt>:except</tt> options can be passed to the layout call. For example:
#
# class WeblogController < ActionController::Base
# layout "weblog_standard", except: :rss
#
# # ...
#
# end
#
# This will assign "weblog_standard" as the WeblogController's layout for all actions except for the +rss+ action, which will
# be rendered directly, without wrapping a layout around the rendered view.
#
# Both the <tt>:only</tt> and <tt>:except</tt> condition can accept an arbitrary number of method references, so
# <tt>except: [ :rss, :text_only ]</tt> is valid, as is <tt>except: :rss</tt>.
#
# == Using a different layout in the action render call
#
# If most of your actions use the same layout, it makes perfect sense to define a controller-wide layout as described above.
# Sometimes you'll have exceptions where one action wants to use a different layout than the rest of the controller.
# You can do this by passing a <tt>:layout</tt> option to the <tt>render</tt> call. For example:
#
# class WeblogController < ActionController::Base
# layout "weblog_standard"
#
# def help
# render action: "help", layout: "help"
# end
# end
#
# This will override the controller-wide "weblog_standard" layout, and will render the help action with the "help" layout instead.
module Layouts
extend ActiveSupport::Concern
include ActionView::Rendering
included do
class_attribute :_layout, instance_accessor: false
class_attribute :_layout_conditions, instance_accessor: false, instance_reader: true, default: {}
_write_layout_method
end
module ClassMethods
def inherited(klass) # :nodoc:
super
klass._write_layout_method
end
# This module is mixed in if layout conditions are provided. This means
# that if no layout conditions are used, this method is not used
module LayoutConditions # :nodoc:
private
# Determines whether the current action has a layout definition by
# checking the action name against the :only and :except conditions
# set by the <tt>layout</tt> method.
#
# ==== Returns
# * <tt>Boolean</tt> - True if the action has a layout definition, false otherwise.
def _conditional_layout?
return unless super
conditions = _layout_conditions
if only = conditions[:only]
only.include?(action_name)
elsif except = conditions[:except]
!except.include?(action_name)
else
true
end
end
end
# Specify the layout to use for this class.
#
# If the specified layout is a:
# String:: the String is the template name
# Symbol:: call the method specified by the symbol
# Proc:: call the passed Proc
# false:: There is no layout
# true:: raise an ArgumentError
# nil:: Force default layout behavior with inheritance
#
# Return value of +Proc+ and +Symbol+ arguments should be +String+, +false+, +true+, or +nil+
# with the same meaning as described above.
#
# ==== Parameters
#
# * <tt>layout</tt> - The layout to use.
#
# ==== Options (conditions)
#
# * +:only+ - A list of actions to apply this layout to.
# * +:except+ - Apply this layout to all actions but this one.
def layout(layout, conditions = {})
include LayoutConditions unless conditions.empty?
conditions.each { |k, v| conditions[k] = Array(v).map(&:to_s) }
self._layout_conditions = conditions
self._layout = layout
_write_layout_method
end
# Creates a _layout method to be called by _default_layout .
#
# If a layout is not explicitly mentioned then look for a layout with the controller's name.
# if nothing is found then try same procedure to find super class's layout.
def _write_layout_method # :nodoc:
silence_redefinition_of_method(:_layout)
prefixes = /\blayouts/.match?(_implied_layout_name) ? [] : ["layouts"]
default_behavior = "lookup_context.find_all('#{_implied_layout_name}', #{prefixes.inspect}, false, [], { formats: formats }).first || super"
name_clause = if name
default_behavior
else
<<-RUBY
super
RUBY
end
layout_definition = \
case _layout
when String
_layout.inspect
when Symbol
<<-RUBY
#{_layout}.tap do |layout|
return #{default_behavior} if layout.nil?
unless layout.is_a?(String) || !layout
raise ArgumentError, "Your layout method :#{_layout} returned \#{layout}. It " \
"should have returned a String, false, or nil"
end
end
RUBY
when Proc
define_method :_layout_from_proc, &_layout
private :_layout_from_proc
<<-RUBY
result = _layout_from_proc(#{_layout.arity == 0 ? '' : 'self'})
return #{default_behavior} if result.nil?
result
RUBY
when false
nil
when true
raise ArgumentError, "Layouts must be specified as a String, Symbol, Proc, false, or nil"
when nil
name_clause
end
class_eval <<-RUBY, __FILE__, __LINE__ + 1
# frozen_string_literal: true
def _layout(lookup_context, formats)
if _conditional_layout?
#{layout_definition}
else
#{name_clause}
end
end
private :_layout
RUBY
end
private
# If no layout is supplied, look for a template named the return
# value of this method.
#
# ==== Returns
# * <tt>String</tt> - A template name
def _implied_layout_name
controller_path
end
end
def _normalize_options(options) # :nodoc:
super
if _include_layout?(options)
layout = options.delete(:layout) { :default }
options[:layout] = _layout_for_option(layout)
end
end
attr_internal_writer :action_has_layout
def initialize(*) # :nodoc:
@_action_has_layout = true
super
end
# Controls whether an action should be rendered using a layout.
# If you want to disable any <tt>layout</tt> settings for the
# current action so that it is rendered without a layout then
# either override this method in your controller to return false
# for that action or set the <tt>action_has_layout</tt> attribute
# to false before rendering.
def action_has_layout?
@_action_has_layout
end
private
def _conditional_layout?
true
end
# This will be overwritten by _write_layout_method
def _layout(*); end
# Determine the layout for a given name, taking into account the name type.
#
# ==== Parameters
# * <tt>name</tt> - The name of the template
def _layout_for_option(name)
case name
when String then _normalize_layout(name)
when Proc then name
when true then Proc.new { |lookup_context, formats| _default_layout(lookup_context, formats, true) }
when :default then Proc.new { |lookup_context, formats| _default_layout(lookup_context, formats, false) }
when false, nil then nil
else
raise ArgumentError,
"String, Proc, :default, true, or false, expected for `layout'; you passed #{name.inspect}"
end
end
def _normalize_layout(value)
value.is_a?(String) && !value.match?(/\blayouts/) ? "layouts/#{value}" : value
end
# Returns the default layout for this controller.
# Optionally raises an exception if the layout could not be found.
#
# ==== Parameters
# * <tt>formats</tt> - The formats accepted to this layout
# * <tt>require_layout</tt> - If set to +true+ and layout is not found,
# an +ArgumentError+ exception is raised (defaults to +false+)
#
# ==== Returns
# * <tt>template</tt> - The template object for the default layout (or +nil+)
def _default_layout(lookup_context, formats, require_layout = false)
begin
value = _layout(lookup_context, formats) if action_has_layout?
rescue NameError => e
raise e, "Could not render layout: #{e.message}"
end
if require_layout && action_has_layout? && !value
raise ArgumentError,
"There was no default layout for #{self.class} in #{view_paths.inspect}"
end
_normalize_layout(value)
end
def _include_layout?(options)
!options.keys.intersect?([:body, :plain, :html, :inline, :partial]) || options.key?(:layout)
end
end
end