Move layouts to AV

1 files changed, 424 insertions, 0 deletions

diff --git a/actionview/lib/action_view/layouts.rb b/actionview/lib/action_view/layouts.rb
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+++ b/actionview/lib/action_view/layouts.rb
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+require "active_support/core_ext/module/remove_method"
+
+
+module ActionView
+  # 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 "shared/header" %>
+  #   Hello World
+  #   <%= render "shared/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 fallbacks 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 fallback "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, :_layout_conditions, :instance_accessor => false
+      self._layout = nil
+      self._layout_conditions = {}
+      _write_layout_method
+    end
+
+    delegate :_layout_conditions, to: :class
+
+    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, which will return the template name
+      # false::  There is no layout
+      # true::   raise an ArgumentError
+      # nil::    Force default layout behavior with inheritance
+      #
+      # ==== 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 {|a| a.to_s} }
+        self._layout_conditions = conditions
+
+        self._layout = layout
+        _write_layout_method
+      end
+
+      # 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 # :nodoc:
+        controller_path
+      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:
+        remove_possible_method(:_layout)
+
+        prefixes    = _implied_layout_name =~ /\blayouts/ ? [] : ["layouts"]
+        default_behavior = "lookup_context.find_all('#{_implied_layout_name}', #{prefixes.inspect}).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
+            protected :_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
+
+        self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
+          def _layout
+            if _conditional_layout?
+              #{layout_definition}
+            else
+              #{name_clause}
+            end
+          end
+          private :_layout
+        RUBY
+      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 { _default_layout(true)  }
+      when :default   then Proc.new { _default_layout(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 !~ /\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>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(require_layout = false)
+      begin
+        value = _layout 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 & [:text, :inline, :partial]).empty? || options.key?(:layout)
+    end
+  end
+end