8 files changed, 1067 insertions, 646 deletions

diff --git a/actionpack/lib/action_dispatch/routing/endpoint.rb b/actionpack/lib/action_dispatch/routing/endpoint.rb
index 88aa13c3e8..28bb20d688 100644
--- a/actionpack/lib/action_dispatch/routing/endpoint.rb
+++ b/actionpack/lib/action_dispatch/routing/endpoint.rb
@@ -1,10 +1,17 @@
+# frozen_string_literal: true
+
 module ActionDispatch
   module Routing
     class Endpoint # :nodoc:
       def dispatcher?;   false; end
       def redirect?;     false; end
-      def matches?(req); true;  end
-      def app;           self;  end
+      def matches?(req);  true; end
+      def app;            self; end
+      def rack_app;        app; end
+
+      def engine?
+        rack_app.is_a?(Class) && rack_app < Rails::Engine
+      end
     end
   end
 end
diff --git a/actionpack/lib/action_dispatch/routing/inspector.rb b/actionpack/lib/action_dispatch/routing/inspector.rb
index 5d30a545a2..413e524ef6 100644
--- a/actionpack/lib/action_dispatch/routing/inspector.rb
+++ b/actionpack/lib/action_dispatch/routing/inspector.rb
@@ -1,5 +1,7 @@
-require 'delegate'
-require 'active_support/core_ext/string/strip'
+# frozen_string_literal: true
+
+require "delegate"
+require "io/console/size"
 
 module ActionDispatch
   module Routing
@@ -13,7 +15,7 @@ module ActionDispatch
       end
 
       def rack_app
-        app.app
+        app.rack_app
       end
 
       def path
@@ -33,11 +35,11 @@ module ActionDispatch
       end
 
       def controller
-        requirements[:controller] || ':controller'
+        parts.include?(:controller) ? ":controller" : requirements[:controller]
       end
 
       def action
-        requirements[:action] || ':action'
+        parts.include?(:action) ? ":action" : requirements[:action]
       end
 
       def internal?
@@ -45,7 +47,7 @@ module ActionDispatch
       end
 
       def engine?
-        rack_app.respond_to?(:routes)
+        app.engine?
       end
     end
 
@@ -59,11 +61,11 @@ module ActionDispatch
         @routes = routes
       end
 
-      def format(formatter, filter = nil)
+      def format(formatter, filter = {})
         routes_to_display = filter_routes(normalize_filter(filter))
         routes = collect_routes(routes_to_display)
         if routes.none?
-          formatter.no_routes(collect_routes(@routes))
+          formatter.no_routes(collect_routes(@routes), filter)
           return formatter.result
         end
 
@@ -79,107 +81,156 @@ module ActionDispatch
       end
 
       private
-
-      def normalize_filter(filter)
-        if filter.is_a?(Hash) && filter[:controller]
-          { controller: /#{filter[:controller].downcase.sub(/_?controller\z/, '').sub('::', '/')}/ }
-        elsif filter
-          { controller: /#{filter}/, action: /#{filter}/, verb: /#{filter}/, name: /#{filter}/, path: /#{filter}/ }
+        def normalize_filter(filter)
+          if filter[:controller]
+            { controller: /#{filter[:controller].underscore.sub(/_?controller\z/, "")}/ }
+          elsif filter[:grep]
+            { controller: /#{filter[:grep]}/, action: /#{filter[:grep]}/,
+              verb: /#{filter[:grep]}/, name: /#{filter[:grep]}/, path: /#{filter[:grep]}/ }
+          end
         end
-      end
 
-      def filter_routes(filter)
-        if filter
-          @routes.select do |route|
-            route_wrapper = RouteWrapper.new(route)
-            filter.any? { |default, value| route_wrapper.send(default) =~ value }
+        def filter_routes(filter)
+          if filter
+            @routes.select do |route|
+              route_wrapper = RouteWrapper.new(route)
+              filter.any? { |default, value| route_wrapper.send(default) =~ value }
+            end
+          else
+            @routes
           end
-        else
-          @routes
         end
-      end
 
-      def collect_routes(routes)
-        routes.collect do |route|
-          RouteWrapper.new(route)
-        end.reject(&:internal?).collect do |route|
-          collect_engine_routes(route)
+        def collect_routes(routes)
+          routes.collect do |route|
+            RouteWrapper.new(route)
+          end.reject(&:internal?).collect do |route|
+            collect_engine_routes(route)
 
-          { name: route.name,
-            verb: route.verb,
-            path: route.path,
-            reqs: route.reqs }
+            { name: route.name,
+              verb: route.verb,
+              path: route.path,
+              reqs: route.reqs }
+          end
         end
-      end
 
-      def collect_engine_routes(route)
-        name = route.endpoint
-        return unless route.engine?
-        return if @engines[name]
+        def collect_engine_routes(route)
+          name = route.endpoint
+          return unless route.engine?
+          return if @engines[name]
 
-        routes = route.rack_app.routes
-        if routes.is_a?(ActionDispatch::Routing::RouteSet)
-          @engines[name] = collect_routes(routes.routes)
+          routes = route.rack_app.routes
+          if routes.is_a?(ActionDispatch::Routing::RouteSet)
+            @engines[name] = collect_routes(routes.routes)
+          end
         end
-      end
     end
 
-    class ConsoleFormatter
-      def initialize
-        @buffer = []
-      end
+    module ConsoleFormatter
+      class Base
+        def initialize
+          @buffer = []
+        end
 
-      def result
-        @buffer.join("\n")
-      end
+        def result
+          @buffer.join("\n")
+        end
 
-      def section_title(title)
-        @buffer << "\n#{title}:"
-      end
+        def section_title(title)
+        end
 
-      def section(routes)
-        @buffer << draw_section(routes)
-      end
+        def section(routes)
+        end
 
-      def header(routes)
-        @buffer << draw_header(routes)
+        def header(routes)
+        end
+
+        def no_routes(routes, filter)
+          @buffer <<
+            if routes.none?
+              <<~MESSAGE
+                You don't have any routes defined!
+
+                Please add some routes in config/routes.rb.
+              MESSAGE
+            elsif filter.key?(:controller)
+              "No routes were found for this controller."
+            elsif filter.key?(:grep)
+              "No routes were found for this grep pattern."
+            end
+
+          @buffer << "For more information about routes, see the Rails guide: https://guides.rubyonrails.org/routing.html."
+        end
       end
 
-      def no_routes(routes)
-        @buffer <<
-        if routes.none?
-          <<-MESSAGE.strip_heredoc
-          You don't have any routes defined!
+      class Sheet < Base
+        def section_title(title)
+          @buffer << "\n#{title}:"
+        end
 
-          Please add some routes in config/routes.rb.
-          MESSAGE
-        else
-          "No routes were found for this controller"
+        def section(routes)
+          @buffer << draw_section(routes)
         end
-        @buffer << "For more information about routes, see the Rails guide: http://guides.rubyonrails.org/routing.html."
-      end
 
-      private
-        def draw_section(routes)
-          header_lengths = ['Prefix', 'Verb', 'URI Pattern'].map(&:length)
-          name_width, verb_width, path_width = widths(routes).zip(header_lengths).map(&:max)
+        def header(routes)
+          @buffer << draw_header(routes)
+        end
+
+        private
 
-          routes.map do |r|
-            "#{r[:name].rjust(name_width)} #{r[:verb].ljust(verb_width)} #{r[:path].ljust(path_width)} #{r[:reqs]}"
+          def draw_section(routes)
+            header_lengths = ["Prefix", "Verb", "URI Pattern"].map(&:length)
+            name_width, verb_width, path_width = widths(routes).zip(header_lengths).map(&:max)
+
+            routes.map do |r|
+              "#{r[:name].rjust(name_width)} #{r[:verb].ljust(verb_width)} #{r[:path].ljust(path_width)} #{r[:reqs]}"
+            end
           end
-        end
 
-        def draw_header(routes)
-          name_width, verb_width, path_width = widths(routes)
+          def draw_header(routes)
+            name_width, verb_width, path_width = widths(routes)
 
-          "#{"Prefix".rjust(name_width)} #{"Verb".ljust(verb_width)} #{"URI Pattern".ljust(path_width)} Controller#Action"
+            "#{"Prefix".rjust(name_width)} #{"Verb".ljust(verb_width)} #{"URI Pattern".ljust(path_width)} Controller#Action"
+          end
+
+          def widths(routes)
+            [routes.map { |r| r[:name].length }.max || 0,
+             routes.map { |r| r[:verb].length }.max || 0,
+             routes.map { |r| r[:path].length }.max || 0]
+          end
+      end
+
+      class Expanded < Base
+        def section_title(title)
+          @buffer << "\n#{"[ #{title} ]"}"
         end
 
-        def widths(routes)
-          [routes.map { |r| r[:name].length }.max || 0,
-           routes.map { |r| r[:verb].length }.max || 0,
-           routes.map { |r| r[:path].length }.max || 0]
+        def section(routes)
+          @buffer << draw_expanded_section(routes)
         end
+
+        private
+
+          def draw_expanded_section(routes)
+            routes.map.each_with_index do |r, i|
+              <<~MESSAGE.chomp
+                #{route_header(index: i + 1)}
+                Prefix            | #{r[:name]}
+                Verb              | #{r[:verb]}
+                URI               | #{r[:path]}
+                Controller#Action | #{r[:reqs]}
+              MESSAGE
+            end
+          end
+
+          def route_header(index:)
+            console_width = IO.console_size.second
+            header_prefix = "--[ Route #{index} ]"
+            dash_remainder = [console_width - header_prefix.size, 0].max
+
+            "#{header_prefix}#{'-' * dash_remainder}"
+          end
+      end
     end
 
     class HtmlTableFormatter
@@ -196,21 +247,21 @@ module ActionDispatch
         @buffer << @view.render(partial: "routes/route", collection: routes)
       end
 
-      # the header is part of the HTML page, so we don't construct it here.
+      # The header is part of the HTML page, so we don't construct it here.
       def header(routes)
       end
 
       def no_routes(*)
-        @buffer << <<-MESSAGE.strip_heredoc
+        @buffer << <<~MESSAGE
           <p>You don't have any routes defined!</p>
           <ul>
             <li>Please add some routes in <tt>config/routes.rb</tt>.</li>
             <li>
               For more information about routes, please see the Rails guide
-              <a href="http://guides.rubyonrails.org/routing.html">Rails Routing from the Outside In</a>.
+              <a href="https://guides.rubyonrails.org/routing.html">Rails Routing from the Outside In</a>.
             </li>
           </ul>
-          MESSAGE
+        MESSAGE
       end
 
       def result
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 81ffea4d5d..08560ccf7d 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -1,10 +1,11 @@
-require 'active_support/core_ext/hash/reverse_merge'
-require 'active_support/core_ext/hash/slice'
-require 'active_support/core_ext/enumerable'
-require 'active_support/core_ext/array/extract_options'
-require 'active_support/core_ext/regexp'
-require 'action_dispatch/routing/redirection'
-require 'action_dispatch/routing/endpoint'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/slice"
+require "active_support/core_ext/enumerable"
+require "active_support/core_ext/array/extract_options"
+require "active_support/core_ext/regexp"
+require "action_dispatch/routing/redirection"
+require "action_dispatch/routing/endpoint"
 
 module ActionDispatch
   module Routing
@@ -18,9 +19,9 @@ module ActionDispatch
         CALL  = ->(app, req) { app.call req.env }
 
         def initialize(app, constraints, strategy)
-          # Unwrap Constraints objects.  I don't actually think it's possible
+          # Unwrap Constraints objects. I don't actually think it's possible
           # to pass a Constraints object to this constructor, but there were
-          # multiple places that kept testing children of this object.  I
+          # multiple places that kept testing children of this object. I
           # *think* they were just being defensive, but I have no idea.
           if app.is_a?(self.class)
             constraints += app.constraints
@@ -42,19 +43,32 @@ module ActionDispatch
         end
 
         def serve(req)
-          return [ 404, {'X-Cascade' => 'pass'}, [] ] unless matches?(req)
+          return [ 404, { "X-Cascade" => "pass" }, [] ] unless matches?(req)
 
           @strategy.call @app, req
         end
 
         private
           def constraint_args(constraint, request)
-            constraint.arity == 1 ? [request] : [request.path_parameters, request]
+            arity = if constraint.respond_to?(:arity)
+              constraint.arity
+            else
+              constraint.method(:call).arity
+            end
+
+            if arity < 1
+              []
+            elsif arity == 1
+              [request]
+            else
+              [request.path_parameters, request]
+            end
           end
       end
 
       class Mapping #:nodoc:
         ANCHOR_CHARACTERS_REGEX = %r{\A(\\A|\^)|(\\Z|\\z|\$)\Z}
+        OPTIONAL_FORMAT_REGEX = %r{(?:\(\.:format\)+|\.:format|/)\Z}
 
         attr_reader :requirements, :defaults
         attr_reader :to, :default_controller, :default_action
@@ -94,7 +108,7 @@ module ActionDispatch
         end
 
         def self.optional_format?(path, format)
-          format != false && !path.include?(':format') && !path.end_with?('/')
+          format != false && path !~ OPTIONAL_FORMAT_REGEX
         end
 
         def initialize(set, ast, defaults, controller, default_action, modyoule, to, formatted, scope_constraints, blocks, via, options_constraints, anchor, options)
@@ -107,7 +121,7 @@ module ActionDispatch
           @ast                = ast
           @anchor             = anchor
           @via                = via
-          @internal           = options[:internal]
+          @internal           = options.delete(:internal)
 
           path_params = ast.find_all(&:symbol?).map(&:to_sym)
 
@@ -121,7 +135,7 @@ module ActionDispatch
 
           if options_constraints.is_a?(Hash)
             @defaults = Hash[options_constraints.find_all { |key, default|
-              URL_OPTIONS.include?(key) && (String === default || Fixnum === default)
+              URL_OPTIONS.include?(key) && (String === default || Integer === default)
             }].merge @defaults
             @blocks = blocks
             constraints.merge! options_constraints
@@ -138,21 +152,16 @@ module ActionDispatch
           @conditions = Hash[conditions]
           @defaults = formats[:defaults].merge(@defaults).merge(normalize_defaults(options))
 
+          if path_params.include?(:action) && !@requirements.key?(:action)
+            @defaults[:action] ||= "index"
+          end
+
           @required_defaults = (split_options[:required_defaults] || []).map(&:first)
         end
 
         def make_route(name, precedence)
-          route = Journey::Route.new(name,
-                            application,
-                            path,
-                            conditions,
-                            required_defaults,
-                            defaults,
-                            request_method,
-                            precedence,
-                            @internal)
-
-          route
+          Journey::Route.new(name, application, path, conditions, required_defaults,
+                             defaults, request_method, precedence, @internal)
         end
 
         def application
@@ -215,7 +224,7 @@ module ActionDispatch
         private
           def add_wildcard_options(options, formatted, path_ast)
             # Add a constraint for wildcard route to make it non-greedy and match the
-            # optional format part of the route by default
+            # optional format part of the route by default.
             if formatted != false
               path_ast.grep(Journey::Nodes::Star).each_with_object({}) { |node, hash|
                 hash[node.name.to_sym] ||= /.+?/
@@ -236,7 +245,7 @@ module ActionDispatch
               options[:controller] ||= /.+?/
             end
 
-            if to.respond_to? :call
+            if to.respond_to?(:action) || to.respond_to?(:call)
               options
             else
               to_endpoint = split_to to
@@ -267,13 +276,13 @@ module ActionDispatch
               { requirements: { format: Regexp.compile(formatted) },
                 defaults:     { format: formatted } }
             else
-              { requirements: { }, defaults: { } }
+              { requirements: {}, defaults: {} }
             end
           end
 
           def verify_regexp_requirements(requirements)
             requirements.each do |requirement|
-              if requirement.source =~ ANCHOR_CHARACTERS_REGEX
+              if ANCHOR_CHARACTERS_REGEX.match?(requirement.source)
                 raise ArgumentError, "Regexp anchor characters are not allowed in routing requirements: #{requirement.inspect}"
               end
 
@@ -288,24 +297,22 @@ module ActionDispatch
           end
 
           def app(blocks)
-            if to.is_a?(Class) && to < ActionController::Metal
+            if to.respond_to?(:action)
               Routing::RouteSet::StaticDispatcher.new to
+            elsif to.respond_to?(:call)
+              Constraints.new(to, blocks, Constraints::CALL)
+            elsif blocks.any?
+              Constraints.new(dispatcher(defaults.key?(:controller)), blocks, Constraints::SERVE)
             else
-              if to.respond_to?(:call)
-                Constraints.new(to, blocks, Constraints::CALL)
-              elsif blocks.any?
-                Constraints.new(dispatcher(defaults.key?(:controller)), blocks, Constraints::SERVE)
-              else
-                dispatcher(defaults.key?(:controller))
-              end
+              dispatcher(defaults.key?(:controller))
             end
           end
 
           def check_controller_and_action(path_params, controller, action)
             hash = check_part(:controller, controller, path_params, {}) do |part|
               translate_controller(part) {
-                message = "'#{part}' is not a supported controller name. This can lead to potential routing problems."
-                message << " See http://guides.rubyonrails.org/routing.html#specifying-a-controller-to-use"
+                message = +"'#{part}' is not a supported controller name. This can lead to potential routing problems."
+                message << " See https://guides.rubyonrails.org/routing.html#specifying-a-controller-to-use"
 
                 raise ArgumentError, message
               }
@@ -329,8 +336,8 @@ module ActionDispatch
           end
 
           def split_to(to)
-            if to =~ /#/
-              to.split('#')
+            if /#/.match?(to)
+              to.split("#")
             else
               []
             end
@@ -338,7 +345,7 @@ module ActionDispatch
 
           def add_controller_module(controller, modyoule)
             if modyoule && !controller.is_a?(Regexp)
-              if controller =~ %r{\A/}
+              if %r{\A/}.match?(controller)
                 controller[1..-1]
               else
                 [modyoule, controller].compact.join("/")
@@ -386,7 +393,7 @@ module ActionDispatch
       # for root cases, where the latter is the correct one.
       def self.normalize_path(path)
         path = Journey::Router::Utils.normalize_path(path)
-        path.gsub!(%r{/(\(+)/?}, '\1/') unless path =~ %r{^/\(+[^)]+\)$}
+        path.gsub!(%r{/(\(+)/?}, '\1/') unless path =~ %r{^/(\(+[^)]+\)){1,}$}
         path
       end
 
@@ -395,7 +402,7 @@ module ActionDispatch
       end
 
       module Base
-        # Matches a url pattern to one or more routes.
+        # Matches a URL pattern to one or more routes.
         #
         # You should not use the +match+ method in your router
         # without specifying an HTTP method.
@@ -405,7 +412,7 @@ module ActionDispatch
         #   # sets :controller, :action and :id in params
         #   match ':controller/:action/:id', via: [:get, :post]
         #
-        # Note that +:controller+, +:action+ and +:id+ are interpreted as url
+        # Note that +:controller+, +:action+ and +:id+ are interpreted as URL
         # query parameters and thus available through +params+ in an action.
         #
         # If you want to expose your action to GET, use +get+ in the router:
@@ -454,7 +461,7 @@ module ActionDispatch
         #
         # === Options
         #
-        # Any options not seen here are passed on as params with the url.
+        # Any options not seen here are passed on as params with the URL.
         #
         # [:controller]
         #   The route's controller.
@@ -469,7 +476,17 @@ module ActionDispatch
         #   <tt>params[<:param>]</tt>.
         #   In your router:
         #
-        #      resources :user, param: :name
+        #      resources :users, param: :name
+        #
+        #   The +users+ resource here will have the following routes generated for it:
+        #
+        #      GET       /users(.:format)
+        #      POST      /users(.:format)
+        #      GET       /users/new(.:format)
+        #      GET       /users/:name/edit(.:format)
+        #      GET       /users/:name(.:format)
+        #      PATCH/PUT /users/:name(.:format)
+        #      DELETE    /users/:name(.:format)
         #
         #   You can override <tt>ActiveRecord::Base#to_param</tt> of a related
         #   model to construct a URL:
@@ -480,8 +497,8 @@ module ActionDispatch
         #        end
         #      end
         #
-        #   user = User.find_by(name: 'Phusion')
-        #   user_path(user)  # => "/users/Phusion"
+        #      user = User.find_by(name: 'Phusion')
+        #      user_path(user)  # => "/users/Phusion"
         #
         # [:path]
         #   The path prefix for the routes.
@@ -539,10 +556,10 @@ module ActionDispatch
         #
         #     match 'json_only', constraints: { format: 'json' }, via: :get
         #
-        #     class Whitelist
+        #     class PermitList
         #       def matches?(request) request.remote_ip == '1.2.3.4' end
         #     end
-        #     match 'path', to: 'c#a', constraints: Whitelist.new, via: :get
+        #     match 'path', to: 'c#a', constraints: PermitList.new, via: :get
         #
         #   See <tt>Scoping#constraints</tt> for more examples with its scope
         #   equivalent.
@@ -565,7 +582,7 @@ module ActionDispatch
         # [:format]
         #   Allows you to specify the default value for optional +format+
         #   segment or disable it by supplying +false+.
-        def match(path, options=nil)
+        def match(path, options = nil)
         end
 
         # Mount a Rack-based application to be used within the application.
@@ -597,7 +614,7 @@ module ActionDispatch
           end
 
           raise ArgumentError, "A rack application must be specified" unless app.respond_to?(:call)
-          raise ArgumentError, <<-MSG.strip_heredoc unless path
+          raise ArgumentError, <<~MSG unless path
             Must be called with mount point
 
               mount SomeRackApp, at: "some_route"
@@ -611,7 +628,7 @@ module ActionDispatch
           target_as       = name_for_action(options[:as], path)
           options[:via] ||= :all
 
-          match(path, options.merge(:to => app, :anchor => false, :format => false))
+          match(path, options.merge(to: app, anchor: false, format: false))
 
           define_generate_prefix(app, target_as) if rails_app
           self
@@ -630,7 +647,7 @@ module ActionDispatch
 
         # Query if the following named route was already defined.
         def has_named_route?(name)
-          @set.named_routes.key? name
+          @set.named_routes.key?(name)
         end
 
         private
@@ -650,18 +667,31 @@ module ActionDispatch
           def define_generate_prefix(app, name)
             _route = @set.named_routes.get name
             _routes = @set
-            app.routes.define_mounted_helper(name)
+            _url_helpers = @set.url_helpers
+
+            script_namer = ->(options) do
+              prefix_options = options.slice(*_route.segment_keys)
+              prefix_options[:relative_url_root] = ""
+
+              if options[:_recall]
+                prefix_options.reverse_merge!(options[:_recall].slice(*_route.segment_keys))
+              end
+
+              # We must actually delete prefix segment keys to avoid passing them to next url_for.
+              _route.segment_keys.each { |k| options.delete(k) }
+              _url_helpers.send("#{name}_path", prefix_options)
+            end
+
+            app.routes.define_mounted_helper(name, script_namer)
+
             app.routes.extend Module.new {
               def optimize_routes_generation?; false; end
+
               define_method :find_script_name do |options|
                 if options.key? :script_name
                   super(options)
                 else
-                  prefix_options = options.slice(*_route.segment_keys)
-                  prefix_options[:relative_url_root] = ''.freeze
-                  # we must actually delete prefix segment keys to avoid passing them to next url_for
-                  _route.segment_keys.each { |k| options.delete(k) }
-                  _routes.url_helpers.send("#{name}_path", prefix_options)
+                  script_namer.call(options)
                 end
               end
             }
@@ -713,11 +743,7 @@ module ActionDispatch
           def map_method(method, args, &block)
             options = args.extract_options!
             options[:via] = method
-            if options.key?(:defaults)
-              defaults(options.delete(:defaults)) { match(*args, options, &block) }
-            else
-              match(*args, options, &block)
-            end
+            match(*args, options, &block)
             self
           end
       end
@@ -811,7 +837,7 @@ module ActionDispatch
           options = args.extract_options!.dup
           scope = {}
 
-          options[:path] = args.flatten.join('/') if args.any?
+          options[:path] = args.flatten.join("/") if args.any?
           options[:constraints] ||= {}
 
           unless nested_scope?
@@ -821,10 +847,10 @@ module ActionDispatch
 
           if options[:constraints].is_a?(Hash)
             defaults = options[:constraints].select do |k, v|
-              URL_OPTIONS.include?(k) && (v.is_a?(String) || v.is_a?(Fixnum))
+              URL_OPTIONS.include?(k) && (v.is_a?(String) || v.is_a?(Integer))
             end
 
-            (options[:defaults] ||= {}).reverse_merge!(defaults)
+            options[:defaults] = defaults.merge(options[:defaults] || {})
           else
             block, options[:constraints] = options[:constraints], {}
           end
@@ -835,7 +861,7 @@ module ActionDispatch
           end
 
           if options.key? :anchor
-            raise ArgumentError, 'anchor is ignored unless passed to `match`'
+            raise ArgumentError, "anchor is ignored unless passed to `match`"
           end
 
           @scope.options.each do |option|
@@ -982,7 +1008,7 @@ module ActionDispatch
         #      resources :iphones
         #    end
         def constraints(constraints = {})
-          scope(:constraints => constraints) { yield }
+          scope(constraints: constraints) { yield }
         end
 
         # Allows you to set default parameters for a route, such as this:
@@ -998,67 +1024,71 @@ module ActionDispatch
         end
 
         private
-          def merge_path_scope(parent, child) #:nodoc:
+          def merge_path_scope(parent, child)
             Mapper.normalize_path("#{parent}/#{child}")
           end
 
-          def merge_shallow_path_scope(parent, child) #:nodoc:
+          def merge_shallow_path_scope(parent, child)
             Mapper.normalize_path("#{parent}/#{child}")
           end
 
-          def merge_as_scope(parent, child) #:nodoc:
+          def merge_as_scope(parent, child)
             parent ? "#{parent}_#{child}" : child
           end
 
-          def merge_shallow_prefix_scope(parent, child) #:nodoc:
+          def merge_shallow_prefix_scope(parent, child)
             parent ? "#{parent}_#{child}" : child
           end
 
-          def merge_module_scope(parent, child) #:nodoc:
+          def merge_module_scope(parent, child)
             parent ? "#{parent}/#{child}" : child
           end
 
-          def merge_controller_scope(parent, child) #:nodoc:
+          def merge_controller_scope(parent, child)
             child
           end
 
-          def merge_action_scope(parent, child) #:nodoc:
+          def merge_action_scope(parent, child)
             child
           end
 
-          def merge_via_scope(parent, child) #:nodoc:
+          def merge_via_scope(parent, child)
             child
           end
 
-          def merge_format_scope(parent, child) #:nodoc:
+          def merge_format_scope(parent, child)
             child
           end
 
-          def merge_path_names_scope(parent, child) #:nodoc:
+          def merge_path_names_scope(parent, child)
             merge_options_scope(parent, child)
           end
 
-          def merge_constraints_scope(parent, child) #:nodoc:
+          def merge_constraints_scope(parent, child)
             merge_options_scope(parent, child)
           end
 
-          def merge_defaults_scope(parent, child) #:nodoc:
+          def merge_defaults_scope(parent, child)
             merge_options_scope(parent, child)
           end
 
-          def merge_blocks_scope(parent, child) #:nodoc:
+          def merge_blocks_scope(parent, child)
             merged = parent ? parent.dup : []
             merged << child if child
             merged
           end
 
-          def merge_options_scope(parent, child) #:nodoc:
+          def merge_options_scope(parent, child)
             (parent || {}).merge(child)
           end
 
-          def merge_shallow_scope(parent, child) #:nodoc:
+          def merge_shallow_scope(parent, child)
             child ? true : false
           end
+
+          def merge_to_scope(parent, child)
+            child
+          end
       end
 
       # Resource routing allows you to quickly declare all of the common routes
@@ -1111,6 +1141,10 @@ module ActionDispatch
           attr_reader :controller, :path, :param
 
           def initialize(entities, api_only, shallow, options = {})
+            if options[:param].to_s.include?(":")
+              raise ArgumentError, ":param option can't contain colons"
+            end
+
             @name       = entities.to_s
             @path       = (options[:path] || @name).to_s
             @controller = (options[:controller] || @name).to_s
@@ -1132,10 +1166,16 @@ module ActionDispatch
           end
 
           def actions
+            if @except
+              available_actions - Array(@except).map(&:to_sym)
+            else
+              available_actions
+            end
+          end
+
+          def available_actions
             if @only
               Array(@only).map(&:to_sym)
-            elsif @except
-              default_actions - Array(@except).map(&:to_sym)
             else
               default_actions
             end
@@ -1237,19 +1277,19 @@ module ActionDispatch
         #
         #   resource :profile
         #
-        # creates six different routes in your application, all mapping to
+        # This creates six different routes in your application, all mapping to
         # the +Profiles+ controller (note that the controller is named after
         # the plural):
         #
         #   GET       /profile/new
-        #   POST      /profile
         #   GET       /profile
         #   GET       /profile/edit
         #   PATCH/PUT /profile
         #   DELETE    /profile
+        #   POST      /profile
         #
         # === Options
-        # Takes same options as +resources+.
+        # Takes same options as resources[rdoc-ref:#resources]
         def resource(*resources, &block)
           options = resources.extract_options!.dup
 
@@ -1264,15 +1304,15 @@ module ActionDispatch
 
               concerns(options[:concerns]) if options[:concerns]
 
-              collection do
-                post :create
-              end if parent_resource.actions.include?(:create)
-
               new do
                 get :new
               end if parent_resource.actions.include?(:new)
 
               set_member_mappings_for_resource
+
+              collection do
+                post :create
+              end if parent_resource.actions.include?(:create)
             end
           end
 
@@ -1314,7 +1354,7 @@ module ActionDispatch
         #   DELETE    /photos/:photo_id/comments/:id
         #
         # === Options
-        # Takes same options as <tt>Base#match</tt> as well as:
+        # Takes same options as match[rdoc-ref:Base#match] as well as:
         #
         # [:path_names]
         #   Allows you to change the segment component of the +edit+ and +new+ actions.
@@ -1322,14 +1362,14 @@ module ActionDispatch
         #
         #     resources :posts, path_names: { new: "brand_new" }
         #
-        #   The above example will now change /posts/new to /posts/brand_new
+        #   The above example will now change /posts/new to /posts/brand_new.
         #
         # [:path]
         #   Allows you to change the path prefix for the resource.
         #
         #     resources :posts, path: 'postings'
         #
-        #   The resource and all segments will now route to /postings instead of /posts
+        #   The resource and all segments will now route to /postings instead of /posts.
         #
         # [:only]
         #   Only generate routes for the given actions.
@@ -1406,6 +1446,9 @@ module ActionDispatch
         #   Allows you to specify the default value for optional +format+
         #   segment or disable it by supplying +false+.
         #
+        # [:param]
+        #   Allows you to override the default param name of +:id+ in the URL.
+        #
         # === Examples
         #
         #   # routes call <tt>Admin::PostsController</tt>
@@ -1526,7 +1569,7 @@ module ActionDispatch
           end
         end
 
-        # See ActionDispatch::Routing::Mapper::Scoping#namespace
+        # See ActionDispatch::Routing::Mapper::Scoping#namespace.
         def namespace(path, options = {})
           if resource_scope?
             nested { super }
@@ -1546,22 +1589,24 @@ module ActionDispatch
           !parent_resource.singleton? && @scope[:shallow]
         end
 
-        # Matches a url pattern to one or more routes.
+        # Matches a URL pattern to one or more routes.
         # For more information, see match[rdoc-ref:Base#match].
         #
-        #   match 'path' => 'controller#action', via: patch
+        #   match 'path' => 'controller#action', via: :patch
         #   match 'path', to: 'controller#action', via: :post
         #   match 'path', 'otherpath', on: :member, via: :get
-        def match(path, *rest)
+        def match(path, *rest, &block)
           if rest.empty? && Hash === path
             options  = path
             path, to = options.find { |name, _value| name.is_a?(String) }
 
+            raise ArgumentError, "Route path not specified" if path.nil?
+
             case to
             when Symbol
               options[:action] = to
             when String
-              if to =~ /#/
+              if /#/.match?(to)
                 options[:to] = to
               else
                 options[:controller] = to
@@ -1577,110 +1622,13 @@ module ActionDispatch
             paths = [path] + rest
           end
 
-          if options[:on] && !VALID_ON_OPTIONS.include?(options[:on])
-            raise ArgumentError, "Unknown scope #{on.inspect} given to :on"
-          end
-
-          if @scope[:controller] && @scope[:action]
-            options[:to] ||= "#{@scope[:controller]}##{@scope[:action]}"
-          end
-
-          controller = options.delete(:controller) || @scope[:controller]
-          option_path = options.delete :path
-          to = options.delete :to
-          via = Mapping.check_via Array(options.delete(:via) {
-            @scope[:via]
-          })
-          formatted = options.delete(:format) { @scope[:format] }
-          anchor = options.delete(:anchor) { true }
-          options_constraints = options.delete(:constraints) || {}
-
-          path_types = paths.group_by(&:class)
-          path_types.fetch(String, []).each do |_path|
-            route_options = options.dup
-            if _path && option_path
-              ActiveSupport::Deprecation.warn <<-eowarn
-Specifying strings for both :path and the route path is deprecated.  Change things like this:
-
-  match #{_path.inspect}, :path => #{option_path.inspect}
-
-to this:
-
-  match #{option_path.inspect}, :as => #{_path.inspect}, :action => #{path.inspect}
-              eowarn
-              route_options[:action] = _path
-              route_options[:as] = _path
-              _path = option_path
-            end
-            to = get_to_from_path(_path, to, route_options[:action])
-            decomposed_match(_path, controller, route_options, _path, to, via, formatted, anchor, options_constraints)
-          end
-
-          path_types.fetch(Symbol, []).each do |action|
-            route_options = options.dup
-            decomposed_match(action, controller, route_options, option_path, to, via, formatted, anchor, options_constraints)
-          end
-
-          self
-        end
-
-        def get_to_from_path(path, to, action)
-          return to if to || action
-
-          path_without_format = path.sub(/\(\.:format\)$/, '')
-          if using_match_shorthand?(path_without_format)
-            path_without_format.gsub(%r{^/}, "").sub(%r{/([^/]*)$}, '#\1').tr("-", "_")
+          if options.key?(:defaults)
+            defaults(options.delete(:defaults)) { map_match(paths, options, &block) }
           else
-            nil
+            map_match(paths, options, &block)
           end
         end
 
-        def using_match_shorthand?(path)
-          path =~ %r{^/?[-\w]+/[-\w/]+$}
-        end
-
-        def decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) # :nodoc:
-          if on = options.delete(:on)
-            send(on) { decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) }
-          else
-            case @scope.scope_level
-            when :resources
-              nested { decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) }
-            when :resource
-              member { decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) }
-            else
-              add_route(path, controller, options, _path, to, via, formatted, anchor, options_constraints)
-            end
-          end
-        end
-
-        def add_route(action, controller, options, _path, to, via, formatted, anchor, options_constraints) # :nodoc:
-          path = path_for_action(action, _path)
-          raise ArgumentError, "path is required" if path.blank?
-
-          action = action.to_s
-
-          default_action = options.delete(:action) || @scope[:action]
-
-          if action =~ /^[\w\-\/]+$/
-            default_action ||= action.tr('-', '_') unless action.include?("/")
-          else
-            action = nil
-          end
-
-          as = if !options.fetch(:as, true) # if it's set to nil or false
-                 options.delete(:as)
-               else
-                 name_for_action(options.delete(:as), action)
-               end
-
-          path = Mapping.normalize_path URI.parser.escape(path), formatted
-          ast = Journey::Parser.parse path
-
-          mapping = Mapping.build(@scope, @set, ast, controller, default_action, to, via, formatted, options_constraints, anchor, options)
-          @set.add_route(mapping, ast, as, anchor)
-        end
-
         # You can specify what Rails should route "/" to with the root method:
         #
         #   root to: 'pages#main'
@@ -1697,7 +1645,7 @@ to this:
         def root(path, options = {})
           if path.is_a?(String)
             options[:to] = path
-          elsif path.is_a?(Hash) and options.empty?
+          elsif path.is_a?(Hash) && options.empty?
             options = path
           else
             raise ArgumentError, "must be called with a path and/or options"
@@ -1714,13 +1662,13 @@ to this:
           end
         end
 
-        protected
+        private
 
-          def parent_resource #:nodoc:
+          def parent_resource
             @scope[:scope_level_resource]
           end
 
-          def apply_common_behavior_for(method, resources, options, &block) #:nodoc:
+          def apply_common_behavior_for(method, resources, options, &block)
             if resources.length > 1
               resources.each { |r| send(method, r, options, &block) }
               return true
@@ -1754,48 +1702,48 @@ to this:
             false
           end
 
-          def apply_action_options(options) # :nodoc:
+          def apply_action_options(options)
             return options if action_options? options
             options.merge scope_action_options
           end
 
-          def action_options?(options) #:nodoc:
+          def action_options?(options)
             options[:only] || options[:except]
           end
 
-          def scope_action_options #:nodoc:
+          def scope_action_options
             @scope[:action_options] || {}
           end
 
-          def resource_scope? #:nodoc:
+          def resource_scope?
             @scope.resource_scope?
           end
 
-          def resource_method_scope? #:nodoc:
+          def resource_method_scope?
             @scope.resource_method_scope?
           end
 
-          def nested_scope? #:nodoc:
+          def nested_scope?
             @scope.nested?
           end
 
-          def with_scope_level(kind)
+          def with_scope_level(kind) # :doc:
             @scope = @scope.new_level(kind)
             yield
           ensure
             @scope = @scope.parent
           end
 
-          def resource_scope(resource) #:nodoc:
-            @scope = @scope.new(:scope_level_resource => resource)
+          def resource_scope(resource)
+            @scope = @scope.new(scope_level_resource: resource)
 
             controller(resource.resource_scope) { yield }
           ensure
             @scope = @scope.parent
           end
 
-          def nested_options #:nodoc:
-            options = { :as => parent_resource.member_name }
+          def nested_options
+            options = { as: parent_resource.member_name }
             options[:constraints] = {
               parent_resource.nested_param => param_constraint
             } if param_constraint?
@@ -1803,27 +1751,27 @@ to this:
             options
           end
 
-          def shallow_nesting_depth #:nodoc:
+          def shallow_nesting_depth
             @scope.find_all { |node|
               node.frame[:scope_level_resource]
             }.count { |node| node.frame[:scope_level_resource].shallow? }
           end
 
-          def param_constraint? #:nodoc:
+          def param_constraint?
             @scope[:constraints] && @scope[:constraints][parent_resource.param].is_a?(Regexp)
           end
 
-          def param_constraint #:nodoc:
+          def param_constraint
             @scope[:constraints][parent_resource.param]
           end
 
-          def canonical_action?(action) #:nodoc:
+          def canonical_action?(action)
             resource_method_scope? && CANONICAL_ACTIONS.include?(action.to_s)
           end
 
-          def shallow_scope #:nodoc:
-            scope = { :as   => @scope[:shallow_prefix],
-                      :path => @scope[:shallow_path] }
+          def shallow_scope
+            scope = { as: @scope[:shallow_prefix],
+                      path: @scope[:shallow_path] }
             @scope = @scope.new scope
 
             yield
@@ -1831,7 +1779,7 @@ to this:
             @scope = @scope.parent
           end
 
-          def path_for_action(action, path) #:nodoc:
+          def path_for_action(action, path)
             return "#{@scope[:path]}/#{path}" if path
 
             if canonical_action?(action)
@@ -1841,23 +1789,23 @@ to this:
             end
           end
 
-          def action_path(name) #:nodoc:
+          def action_path(name)
             @scope[:path_names][name.to_sym] || name
           end
 
-          def prefix_name_for_action(as, action) #:nodoc:
+          def prefix_name_for_action(as, action)
             if as
               prefix = as
             elsif !canonical_action?(action)
               prefix = action
             end
 
-            if prefix && prefix != '/' && !prefix.empty?
-              Mapper.normalize_name prefix.to_s.tr('-', '_')
+            if prefix && prefix != "/" && !prefix.empty?
+              Mapper.normalize_name prefix.to_s.tr("-", "_")
             end
           end
 
-          def name_for_action(as, action) #:nodoc:
+          def name_for_action(as, action)
             prefix = prefix_name_for_action(as, action)
             name_prefix = @scope[:as]
 
@@ -1869,7 +1817,7 @@ to this:
             end
 
             action_name = @scope.action_name(name_prefix, prefix, collection_name, member_name)
-            candidate = action_name.select(&:present?).join('_')
+            candidate = action_name.select(&:present?).join("_")
 
             unless candidate.empty?
               # If a name was not explicitly given, we check if it is valid
@@ -1883,7 +1831,7 @@ to this:
             end
           end
 
-          def set_member_mappings_for_resource
+          def set_member_mappings_for_resource # :doc:
             member do
               get :edit if parent_resource.actions.include?(:edit)
               get :show if parent_resource.actions.include?(:show)
@@ -1895,22 +1843,119 @@ to this:
             end
           end
 
-          def api_only?
+          def api_only? # :doc:
             @set.api_only?
           end
-        private
 
-        def path_scope(path)
-          @scope = @scope.new(path: merge_path_scope(@scope[:path], path))
-          yield
-        ensure
-          @scope = @scope.parent
-        end
+          def path_scope(path)
+            @scope = @scope.new(path: merge_path_scope(@scope[:path], path))
+            yield
+          ensure
+            @scope = @scope.parent
+          end
 
-        def match_root_route(options)
-          name = has_named_route?(:root) ? nil : :root
-          match '/', { :as => name, :via => :get }.merge!(options)
-        end
+          def map_match(paths, options)
+            if options[:on] && !VALID_ON_OPTIONS.include?(options[:on])
+              raise ArgumentError, "Unknown scope #{on.inspect} given to :on"
+            end
+
+            if @scope[:to]
+              options[:to] ||= @scope[:to]
+            end
+
+            if @scope[:controller] && @scope[:action]
+              options[:to] ||= "#{@scope[:controller]}##{@scope[:action]}"
+            end
+
+            controller = options.delete(:controller) || @scope[:controller]
+            option_path = options.delete :path
+            to = options.delete :to
+            via = Mapping.check_via Array(options.delete(:via) {
+              @scope[:via]
+            })
+            formatted = options.delete(:format) { @scope[:format] }
+            anchor = options.delete(:anchor) { true }
+            options_constraints = options.delete(:constraints) || {}
+
+            path_types = paths.group_by(&:class)
+            path_types.fetch(String, []).each do |_path|
+              route_options = options.dup
+              if _path && option_path
+                raise ArgumentError, "Ambiguous route definition. Both :path and the route path were specified as strings."
+              end
+              to = get_to_from_path(_path, to, route_options[:action])
+              decomposed_match(_path, controller, route_options, _path, to, via, formatted, anchor, options_constraints)
+            end
+
+            path_types.fetch(Symbol, []).each do |action|
+              route_options = options.dup
+              decomposed_match(action, controller, route_options, option_path, to, via, formatted, anchor, options_constraints)
+            end
+
+            self
+          end
+
+          def get_to_from_path(path, to, action)
+            return to if to || action
+
+            path_without_format = path.sub(/\(\.:format\)$/, "")
+            if using_match_shorthand?(path_without_format)
+              path_without_format.gsub(%r{^/}, "").sub(%r{/([^/]*)$}, '#\1').tr("-", "_")
+            else
+              nil
+            end
+          end
+
+          def using_match_shorthand?(path)
+            path =~ %r{^/?[-\w]+/[-\w/]+$}
+          end
+
+          def decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints)
+            if on = options.delete(:on)
+              send(on) { decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) }
+            else
+              case @scope.scope_level
+              when :resources
+                nested { decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) }
+              when :resource
+                member { decomposed_match(path, controller, options, _path, to, via, formatted, anchor, options_constraints) }
+              else
+                add_route(path, controller, options, _path, to, via, formatted, anchor, options_constraints)
+              end
+            end
+          end
+
+          def add_route(action, controller, options, _path, to, via, formatted, anchor, options_constraints)
+            path = path_for_action(action, _path)
+            raise ArgumentError, "path is required" if path.blank?
+
+            action = action.to_s
+
+            default_action = options.delete(:action) || @scope[:action]
+
+            if /^[\w\-\/]+$/.match?(action)
+              default_action ||= action.tr("-", "_") unless action.include?("/")
+            else
+              action = nil
+            end
+
+            as = if !options.fetch(:as, true) # if it's set to nil or false
+              options.delete(:as)
+            else
+              name_for_action(options.delete(:as), action)
+            end
+
+            path = Mapping.normalize_path URI.parser.escape(path), formatted
+            ast = Journey::Parser.parse path
+
+            mapping = Mapping.build(@scope, @set, ast, controller, default_action, to, via, formatted, options_constraints, anchor, options)
+            @set.add_route(mapping, as)
+          end
+
+          def match_root_route(options)
+            args = ["/", { as: :root, via: :get }.merge(options)]
+            match(*args)
+          end
       end
 
       # Routing Concerns allow you to declare common routes that can be reused
@@ -2001,7 +2046,7 @@ to this:
         #     concerns :commentable
         #   end
         #
-        # concerns also work in any routes helper that you want to use:
+        # Concerns also work in any routes helper that you want to use:
         #
         #   namespace :posts do
         #     concerns :commentable
@@ -2018,10 +2063,124 @@ to this:
         end
       end
 
+      module CustomUrls
+        # Define custom URL helpers that will be added to the application's
+        # routes. This allows you to override and/or replace the default behavior
+        # of routing helpers, e.g:
+        #
+        #   direct :homepage do
+        #     "http://www.rubyonrails.org"
+        #   end
+        #
+        #   direct :commentable do |model|
+        #     [ model, anchor: model.dom_id ]
+        #   end
+        #
+        #   direct :main do
+        #     { controller: "pages", action: "index", subdomain: "www" }
+        #   end
+        #
+        # The return value from the block passed to +direct+ must be a valid set of
+        # arguments for +url_for+ which will actually build the URL string. This can
+        # be one of the following:
+        #
+        # * A string, which is treated as a generated URL
+        # * A hash, e.g. <tt>{ controller: "pages", action: "index" }</tt>
+        # * An array, which is passed to +polymorphic_url+
+        # * An Active Model instance
+        # * An Active Model class
+        #
+        # NOTE: Other URL helpers can be called in the block but be careful not to invoke
+        # your custom URL helper again otherwise it will result in a stack overflow error.
+        #
+        # You can also specify default options that will be passed through to
+        # your URL helper definition, e.g:
+        #
+        #   direct :browse, page: 1, size: 10 do |options|
+        #     [ :products, options.merge(params.permit(:page, :size).to_h.symbolize_keys) ]
+        #   end
+        #
+        # In this instance the +params+ object comes from the context in which the
+        # block is executed, e.g. generating a URL inside a controller action or a view.
+        # If the block is executed where there isn't a +params+ object such as this:
+        #
+        #   Rails.application.routes.url_helpers.browse_path
+        #
+        # then it will raise a +NameError+. Because of this you need to be aware of the
+        # context in which you will use your custom URL helper when defining it.
+        #
+        # NOTE: The +direct+ method can't be used inside of a scope block such as
+        # +namespace+ or +scope+ and will raise an error if it detects that it is.
+        def direct(name, options = {}, &block)
+          unless @scope.root?
+            raise RuntimeError, "The direct method can't be used inside a routes scope block"
+          end
+
+          @set.add_url_helper(name, options, &block)
+        end
+
+        # Define custom polymorphic mappings of models to URLs. This alters the
+        # behavior of +polymorphic_url+ and consequently the behavior of
+        # +link_to+ and +form_for+ when passed a model instance, e.g:
+        #
+        #   resource :basket
+        #
+        #   resolve "Basket" do
+        #     [:basket]
+        #   end
+        #
+        # This will now generate "/basket" when a +Basket+ instance is passed to
+        # +link_to+ or +form_for+ instead of the standard "/baskets/:id".
+        #
+        # NOTE: This custom behavior only applies to simple polymorphic URLs where
+        # a single model instance is passed and not more complicated forms, e.g:
+        #
+        #   # config/routes.rb
+        #   resource :profile
+        #   namespace :admin do
+        #     resources :users
+        #   end
+        #
+        #   resolve("User") { [:profile] }
+        #
+        #   # app/views/application/_menu.html.erb
+        #   link_to "Profile", @current_user
+        #   link_to "Profile", [:admin, @current_user]
+        #
+        # The first +link_to+ will generate "/profile" but the second will generate
+        # the standard polymorphic URL of "/admin/users/1".
+        #
+        # You can pass options to a polymorphic mapping - the arity for the block
+        # needs to be two as the instance is passed as the first argument, e.g:
+        #
+        #   resolve "Basket", anchor: "items" do |basket, options|
+        #     [:basket, options]
+        #   end
+        #
+        # This generates the URL "/basket#items" because when the last item in an
+        # array passed to +polymorphic_url+ is a hash then it's treated as options
+        # to the URL helper that gets called.
+        #
+        # NOTE: The +resolve+ method can't be used inside of a scope block such as
+        # +namespace+ or +scope+ and will raise an error if it detects that it is.
+        def resolve(*args, &block)
+          unless @scope.root?
+            raise RuntimeError, "The resolve method can't be used inside a routes scope block"
+          end
+
+          options = args.extract_options!
+          args = args.flatten(1)
+
+          args.each do |klass|
+            @set.add_polymorphic_mapping(klass, options, &block)
+          end
+        end
+      end
+
       class Scope # :nodoc:
         OPTIONS = [:path, :shallow_path, :as, :shallow_prefix, :module,
                    :controller, :action, :path_names, :constraints,
-                   :shallow, :blocks, :defaults, :via, :format, :options]
+                   :shallow, :blocks, :defaults, :via, :format, :options, :to]
 
         RESOURCE_SCOPES = [:resource, :resources]
         RESOURCE_METHOD_SCOPES = [:collection, :member, :new]
@@ -2038,6 +2197,14 @@ to this:
           scope_level == :nested
         end
 
+        def null?
+          @hash.nil? && @parent.nil?
+        end
+
+        def root?
+          @parent.null?
+        end
+
         def resources?
           scope_level == :resources
         end
@@ -2088,8 +2255,7 @@ to this:
 
         def each
           node = self
-          loop do
-            break if node.equal? NULL
+          until node.equal? NULL
             yield node
             node = node.parent
           end
@@ -2102,7 +2268,7 @@ to this:
 
       def initialize(set) #:nodoc:
         @set = set
-        @scope = Scope.new({ :path_names => @set.resources_path_names })
+        @scope = Scope.new(path_names: @set.resources_path_names)
         @concerns = {}
       end
 
@@ -2112,6 +2278,7 @@ to this:
       include Scoping
       include Concerns
       include Resources
+      include CustomUrls
     end
   end
 end
diff --git a/actionpack/lib/action_dispatch/routing/polymorphic_routes.rb b/actionpack/lib/action_dispatch/routing/polymorphic_routes.rb
index 9934f5547a..4de5f9e2f7 100644
--- a/actionpack/lib/action_dispatch/routing/polymorphic_routes.rb
+++ b/actionpack/lib/action_dispatch/routing/polymorphic_routes.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module ActionDispatch
   module Routing
     # Polymorphic URL helpers are methods for smart resolution to a named route call when
     # given an Active Record model instance. They are to be used in combination with
     # ActionController::Resources.
     #
-    # These methods are useful when you want to generate correct URL or path to a RESTful
+    # These methods are useful when you want to generate the correct URL or path to a RESTful
     # resource without having to know the exact type of the record in question.
     #
     # Nested resources and/or namespaces are also supported, as illustrated in the example:
@@ -40,7 +42,7 @@ module ActionDispatch
     #
     # Example usage:
     #
-    #   edit_polymorphic_path(@post)              # => "/posts/1/edit"
+    #   edit_polymorphic_path(@post)           # => "/posts/1/edit"
     #   polymorphic_path(@post, format: :pdf)  # => "/posts/1.pdf"
     #
     # == Usage with mounted engines
@@ -79,7 +81,7 @@ module ActionDispatch
       #   polymorphic_url([blog, post], anchor: 'my_anchor', script_name: "/my_app")
       #     # => "http://example.com/my_app/blogs/1/posts/1#my_anchor"
       #
-      # For all of these options, see the documentation for <tt>url_for</tt>.
+      # For all of these options, see the documentation for {url_for}[rdoc-ref:ActionDispatch::Routing::UrlFor].
       #
       # ==== Functionality
       #
@@ -103,6 +105,10 @@ module ActionDispatch
           return polymorphic_url record, options
         end
 
+        if mapping = polymorphic_mapping(record_or_hash_or_array)
+          return mapping.call(self, [record_or_hash_or_array, options], false)
+        end
+
         opts   = options.dup
         action = opts.delete :action
         type   = opts.delete(:routing_type) || :url
@@ -114,8 +120,7 @@ module ActionDispatch
                                                opts
       end
 
-      # Returns the path component of a URL for the given record. It uses
-      # <tt>polymorphic_url</tt> with <tt>routing_type: :path</tt>.
+      # Returns the path component of a URL for the given record.
       def polymorphic_path(record_or_hash_or_array, options = {})
         if Hash === record_or_hash_or_array
           options = record_or_hash_or_array.merge(options)
@@ -123,6 +128,10 @@ module ActionDispatch
           return polymorphic_path record, options
         end
 
+        if mapping = polymorphic_mapping(record_or_hash_or_array)
+          return mapping.call(self, [record_or_hash_or_array, options], true)
+        end
+
         opts   = options.dup
         action = opts.delete :action
         type   = :path
@@ -134,7 +143,6 @@ module ActionDispatch
                                                opts
       end
 
-
       %w(edit new).each do |action|
         module_eval <<-EOT, __FILE__, __LINE__ + 1
           def #{action}_polymorphic_url(record_or_hash, options = {})
@@ -149,176 +157,195 @@ module ActionDispatch
 
       private
 
-      def polymorphic_url_for_action(action, record_or_hash, options)
-        polymorphic_url(record_or_hash, options.merge(:action => action))
-      end
-
-      def polymorphic_path_for_action(action, record_or_hash, options)
-        polymorphic_path(record_or_hash, options.merge(:action => action))
-      end
-
-      class HelperMethodBuilder # :nodoc:
-        CACHE = { 'path' => {}, 'url' => {} }
-
-        def self.get(action, type)
-          type   = type.to_s
-          CACHE[type].fetch(action) { build action, type }
+        def polymorphic_url_for_action(action, record_or_hash, options)
+          polymorphic_url(record_or_hash, options.merge(action: action))
         end
 
-        def self.url;  CACHE['url'.freeze][nil]; end
-        def self.path; CACHE['path'.freeze][nil]; end
+        def polymorphic_path_for_action(action, record_or_hash, options)
+          polymorphic_path(record_or_hash, options.merge(action: action))
+        end
 
-        def self.build(action, type)
-          prefix = action ? "#{action}_" : ""
-          suffix = type
-          if action.to_s == 'new'
-            HelperMethodBuilder.singular prefix, suffix
+        def polymorphic_mapping(record)
+          if record.respond_to?(:to_model)
+            _routes.polymorphic_mappings[record.to_model.model_name.name]
           else
-            HelperMethodBuilder.plural prefix, suffix
+            _routes.polymorphic_mappings[record.class.name]
           end
         end
 
-        def self.singular(prefix, suffix)
-          new(->(name) { name.singular_route_key }, prefix, suffix)
-        end
+        class HelperMethodBuilder # :nodoc:
+          CACHE = { "path" => {}, "url" => {} }
 
-        def self.plural(prefix, suffix)
-          new(->(name) { name.route_key }, prefix, suffix)
-        end
+          def self.get(action, type)
+            type = type.to_s
+            CACHE[type].fetch(action) { build action, type }
+          end
 
-        def self.polymorphic_method(recipient, record_or_hash_or_array, action, type, options)
-          builder = get action, type
+          def self.url;  CACHE["url"][nil]; end
+          def self.path; CACHE["path"][nil]; end
 
-          case record_or_hash_or_array
-          when Array
-            record_or_hash_or_array = record_or_hash_or_array.compact
-            if record_or_hash_or_array.empty?
-              raise ArgumentError, "Nil location provided. Can't build URI."
-            end
-            if record_or_hash_or_array.first.is_a?(ActionDispatch::Routing::RoutesProxy)
-              recipient = record_or_hash_or_array.shift
+          def self.build(action, type)
+            prefix = action ? "#{action}_" : ""
+            suffix = type
+            if action.to_s == "new"
+              HelperMethodBuilder.singular prefix, suffix
+            else
+              HelperMethodBuilder.plural prefix, suffix
             end
-
-            method, args = builder.handle_list record_or_hash_or_array
-          when String, Symbol
-            method, args = builder.handle_string record_or_hash_or_array
-          when Class
-            method, args = builder.handle_class record_or_hash_or_array
-
-          when nil
-            raise ArgumentError, "Nil location provided. Can't build URI."
-          else
-            method, args = builder.handle_model record_or_hash_or_array
           end
 
+          def self.singular(prefix, suffix)
+            new(->(name) { name.singular_route_key }, prefix, suffix)
+          end
 
-          if options.empty?
-            recipient.send(method, *args)
-          else
-            recipient.send(method, *args, options)
+          def self.plural(prefix, suffix)
+            new(->(name) { name.route_key }, prefix, suffix)
           end
-        end
 
-        attr_reader :suffix, :prefix
+          def self.polymorphic_method(recipient, record_or_hash_or_array, action, type, options)
+            builder = get action, type
+
+            case record_or_hash_or_array
+            when Array
+              record_or_hash_or_array = record_or_hash_or_array.compact
+              if record_or_hash_or_array.empty?
+                raise ArgumentError, "Nil location provided. Can't build URI."
+              end
+              if record_or_hash_or_array.first.is_a?(ActionDispatch::Routing::RoutesProxy)
+                recipient = record_or_hash_or_array.shift
+              end
+
+              method, args = builder.handle_list record_or_hash_or_array
+            when String, Symbol
+              method, args = builder.handle_string record_or_hash_or_array
+            when Class
+              method, args = builder.handle_class record_or_hash_or_array
 
-        def initialize(key_strategy, prefix, suffix)
-          @key_strategy = key_strategy
-          @prefix       = prefix
-          @suffix       = suffix
-        end
+            when nil
+              raise ArgumentError, "Nil location provided. Can't build URI."
+            else
+              method, args = builder.handle_model record_or_hash_or_array
+            end
 
-        def handle_string(record)
-          [get_method_for_string(record), []]
-        end
+            if options.empty?
+              recipient.send(method, *args)
+            else
+              recipient.send(method, *args, options)
+            end
+          end
 
-        def handle_string_call(target, str)
-          target.send get_method_for_string str
-        end
+          attr_reader :suffix, :prefix
 
-        def handle_class(klass)
-          [get_method_for_class(klass), []]
-        end
+          def initialize(key_strategy, prefix, suffix)
+            @key_strategy = key_strategy
+            @prefix       = prefix
+            @suffix       = suffix
+          end
 
-        def handle_class_call(target, klass)
-          target.send get_method_for_class klass
-        end
+          def handle_string(record)
+            [get_method_for_string(record), []]
+          end
 
-        def handle_model(record)
-          args  = []
+          def handle_string_call(target, str)
+            target.send get_method_for_string str
+          end
 
-          model = record.to_model
-          named_route = if model.persisted?
-                          args << model
-                          get_method_for_string model.model_name.singular_route_key
-                        else
-                          get_method_for_class model
-                        end
+          def handle_class(klass)
+            [get_method_for_class(klass), []]
+          end
 
-          [named_route, args]
-        end
+          def handle_class_call(target, klass)
+            target.send get_method_for_class klass
+          end
 
-        def handle_model_call(target, model)
-          method, args = handle_model model
-          target.send(method, *args)
-        end
+          def handle_model(record)
+            args  = []
 
-        def handle_list(list)
-          record_list = list.dup
-          record      = record_list.pop
+            model = record.to_model
+            named_route = if model.persisted?
+              args << model
+              get_method_for_string model.model_name.singular_route_key
+            else
+              get_method_for_class model
+            end
 
-          args = []
+            [named_route, args]
+          end
 
-          route  = record_list.map { |parent|
-            case parent
-            when Symbol, String
-              parent.to_s
-            when Class
-              args << parent
-              parent.model_name.singular_route_key
+          def handle_model_call(target, record)
+            if mapping = polymorphic_mapping(target, record)
+              mapping.call(target, [record], suffix == "path")
             else
-              args << parent.to_model
-              parent.to_model.model_name.singular_route_key
+              method, args = handle_model(record)
+              target.send(method, *args)
             end
-          }
-
-          route <<
-          case record
-          when Symbol, String
-            record.to_s
-          when Class
-            @key_strategy.call record.model_name
-          else
-            model = record.to_model
-            if model.persisted?
-              args << model
-              model.model_name.singular_route_key
+          end
+
+          def handle_list(list)
+            record_list = list.dup
+            record      = record_list.pop
+
+            args = []
+
+            route = record_list.map { |parent|
+              case parent
+              when Symbol, String
+                parent.to_s
+              when Class
+                args << parent
+                parent.model_name.singular_route_key
+              else
+                args << parent.to_model
+                parent.to_model.model_name.singular_route_key
+              end
+            }
+
+            route <<
+            case record
+            when Symbol, String
+              record.to_s
+            when Class
+              @key_strategy.call record.model_name
             else
-              @key_strategy.call model.model_name
+              model = record.to_model
+              if model.persisted?
+                args << model
+                model.model_name.singular_route_key
+              else
+                @key_strategy.call model.model_name
+              end
             end
-          end
 
-          route << suffix
+            route << suffix
 
-          named_route = prefix + route.join("_")
-          [named_route, args]
-        end
+            named_route = prefix + route.join("_")
+            [named_route, args]
+          end
 
-        private
+          private
 
-        def get_method_for_class(klass)
-          name   = @key_strategy.call klass.model_name
-          get_method_for_string name
-        end
+            def polymorphic_mapping(target, record)
+              if record.respond_to?(:to_model)
+                target._routes.polymorphic_mappings[record.to_model.model_name.name]
+              else
+                target._routes.polymorphic_mappings[record.class.name]
+              end
+            end
 
-        def get_method_for_string(str)
-          "#{prefix}#{str}_#{suffix}"
-        end
+            def get_method_for_class(klass)
+              name = @key_strategy.call klass.model_name
+              get_method_for_string name
+            end
 
-        [nil, 'new', 'edit'].each do |action|
-          CACHE['url'][action]  = build action, 'url'
-          CACHE['path'][action] = build action, 'path'
+            def get_method_for_string(str)
+              "#{prefix}#{str}_#{suffix}"
+            end
+
+            [nil, "new", "edit"].each do |action|
+              CACHE["url"][action]  = build action, "url"
+              CACHE["path"][action] = build action, "path"
+            end
         end
-      end
     end
   end
 end
diff --git a/actionpack/lib/action_dispatch/routing/redirection.rb b/actionpack/lib/action_dispatch/routing/redirection.rb
index d6987f4d09..143a4b3d62 100644
--- a/actionpack/lib/action_dispatch/routing/redirection.rb
+++ b/actionpack/lib/action_dispatch/routing/redirection.rb
@@ -1,9 +1,11 @@
-require 'action_dispatch/http/request'
-require 'active_support/core_ext/uri'
-require 'active_support/core_ext/array/extract_options'
-require 'rack/utils'
-require 'action_controller/metal/exceptions'
-require 'action_dispatch/routing/endpoint'
+# frozen_string_literal: true
+
+require "action_dispatch/http/request"
+require "active_support/core_ext/uri"
+require "active_support/core_ext/array/extract_options"
+require "rack/utils"
+require "action_controller/metal/exceptions"
+require "action_dispatch/routing/endpoint"
 
 module ActionDispatch
   module Routing
@@ -22,7 +24,6 @@ module ActionDispatch
       end
 
       def serve(req)
-        req.check_path_parameters!
         uri = URI.parse(path(req.path_parameters, req))
 
         unless uri.host
@@ -37,12 +38,14 @@ module ActionDispatch
         uri.host   ||= req.host
         uri.port   ||= req.port unless req.standard_port?
 
+        req.commit_flash
+
         body = %(<html><body>You are being <a href="#{ERB::Util.unwrapped_html_escape(uri.to_s)}">redirected</a>.</body></html>)
 
         headers = {
-          'Location' => uri.to_s,
-          'Content-Type' => 'text/html',
-          'Content-Length' => body.length.to_s
+          "Location" => uri.to_s,
+          "Content-Type" => "text/html",
+          "Content-Length" => body.length.to_s
         }
 
         [ status, headers, [body] ]
@@ -58,19 +61,19 @@ module ActionDispatch
 
       private
         def relative_path?(path)
-          path && !path.empty? && path[0] != '/'
+          path && !path.empty? && path[0] != "/"
         end
 
         def escape(params)
-          Hash[params.map{ |k,v| [k, Rack::Utils.escape(v)] }]
+          Hash[params.map { |k, v| [k, Rack::Utils.escape(v)] }]
         end
 
         def escape_fragment(params)
-          Hash[params.map{ |k,v| [k, Journey::Router::Utils.escape_fragment(v)] }]
+          Hash[params.map { |k, v| [k, Journey::Router::Utils.escape_fragment(v)] }]
         end
 
         def escape_path(params)
-          Hash[params.map{ |k,v| [k, Journey::Router::Utils.escape_path(v)] }]
+          Hash[params.map { |k, v| [k, Journey::Router::Utils.escape_path(v)] }]
         end
     end
 
@@ -104,11 +107,11 @@ module ActionDispatch
 
       def path(params, request)
         url_options = {
-          :protocol => request.protocol,
-          :host     => request.host,
-          :port     => request.optional_port,
-          :path     => request.path,
-          :params   => request.query_parameters
+          protocol: request.protocol,
+          host: request.host,
+          port: request.optional_port,
+          path: request.path,
+          params: request.query_parameters
         }.merge! options
 
         if !params.empty? && url_options[:path].match(/%\{\w*\}/)
@@ -129,21 +132,23 @@ module ActionDispatch
       end
 
       def inspect
-        "redirect(#{status}, #{options.map{ |k,v| "#{k}: #{v}" }.join(', ')})"
+        "redirect(#{status}, #{options.map { |k, v| "#{k}: #{v}" }.join(', ')})"
       end
     end
 
     module Redirection
-
       # Redirect any path to another path:
       #
       #   get "/stories" => redirect("/posts")
       #
+      # This will redirect the user, while ignoring certain parts of the request, including query string, etc.
+      # <tt>/stories</tt>, <tt>/stories?foo=bar</tt>, etc all redirect to <tt>/posts</tt>.
+      #
       # You can also use interpolation in the supplied redirect argument:
       #
       #   get 'docs/:article', to: redirect('/wiki/%{article}')
       #
-      # Note that if you return a path without a leading slash then the url is prefixed with the
+      # Note that if you return a path without a leading slash then the URL is prefixed with the
       # current SCRIPT_NAME environment variable. This is typically '/' but may be different in
       # a mounted engine or where the application is deployed to a subdirectory of a website.
       #
@@ -162,11 +167,16 @@ module ActionDispatch
       # Note that the +do end+ syntax for the redirect block wouldn't work, as Ruby would pass
       # the block to +get+ instead of +redirect+. Use <tt>{ ... }</tt> instead.
       #
-      # The options version of redirect allows you to supply only the parts of the url which need
+      # The options version of redirect allows you to supply only the parts of the URL which need
       # to change, it also supports interpolation of the path similar to the first example.
       #
       #   get 'stores/:name',       to: redirect(subdomain: 'stores', path: '/%{name}')
       #   get 'stores/:name(*all)', to: redirect(subdomain: 'stores', path: '/%{name}%{all}')
+      #   get '/stories', to: redirect(path: '/posts')
+      #
+      # This will redirect the user, while changing only the specified parts of the request,
+      # for example the +path+ option in the last example.
+      # <tt>/stories</tt>, <tt>/stories?foo=bar</tt>, redirect to <tt>/posts</tt> and <tt>/posts?foo=bar</tt> respectively.
       #
       # Finally, an object which responds to call can be supplied to redirect, allowing you to reuse
       # common redirect routes. The call method must accept two arguments, params and request, and return
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index 85f202b823..d0a7eadf45 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -1,12 +1,13 @@
-require 'action_dispatch/journey'
-require 'active_support/concern'
-require 'active_support/core_ext/object/to_query'
-require 'active_support/core_ext/hash/slice'
-require 'active_support/core_ext/module/remove_method'
-require 'active_support/core_ext/array/extract_options'
-require 'action_controller/metal/exceptions'
-require 'action_dispatch/http/request'
-require 'action_dispatch/routing/endpoint'
+# frozen_string_literal: true
+
+require "action_dispatch/journey"
+require "active_support/core_ext/object/to_query"
+require "active_support/core_ext/module/redefine_method"
+require "active_support/core_ext/module/remove_method"
+require "active_support/core_ext/array/extract_options"
+require "action_controller/metal/exceptions"
+require "action_dispatch/http/request"
+require "action_dispatch/routing/endpoint"
 
 module ActionDispatch
   module Routing
@@ -34,7 +35,7 @@ module ActionDispatch
           if @raise_on_name_error
             raise
           else
-            return [404, {'X-Cascade' => 'pass'}, []]
+            [404, { "X-Cascade" => "pass" }, []]
           end
         end
 
@@ -59,7 +60,7 @@ module ActionDispatch
 
         private
 
-        def controller(_); @controller_class; end
+          def controller(_); @controller_class; end
       end
 
       # A NamedRouteCollection instance is a collection of named routes, and also
@@ -71,7 +72,7 @@ module ActionDispatch
         private :routes
 
         def initialize
-          @routes  = {}
+          @routes = {}
           @path_helpers = Set.new
           @url_helpers = Set.new
           @url_helpers_module  = Module.new
@@ -89,11 +90,11 @@ module ActionDispatch
 
         def clear!
           @path_helpers.each do |helper|
-            @path_helpers_module.send :undef_method, helper
+            @path_helpers_module.remove_method helper
           end
 
           @url_helpers.each do |helper|
-            @url_helpers_module.send  :undef_method, helper
+            @url_helpers_module.remove_method helper
           end
 
           @routes.clear
@@ -107,8 +108,8 @@ module ActionDispatch
           url_name  = :"#{name}_url"
 
           if routes.key? key
-            @path_helpers_module.send :undef_method, path_name
-            @url_helpers_module.send  :undef_method, url_name
+            @path_helpers_module.undef_method path_name
+            @url_helpers_module.undef_method url_name
           end
           routes[key] = route
           define_url_helper @path_helpers_module, route, path_name, route.defaults, name, PATH
@@ -144,6 +145,31 @@ module ActionDispatch
           routes.length
         end
 
+        # Given a +name+, defines name_path and name_url helpers.
+        # Used by 'direct', 'resolve', and 'polymorphic' route helpers.
+        def add_url_helper(name, defaults, &block)
+          helper = CustomUrlHelper.new(name, defaults, &block)
+          path_name = :"#{name}_path"
+          url_name = :"#{name}_url"
+
+          @path_helpers_module.module_eval do
+            redefine_method(path_name) do |*args|
+              helper.call(self, args, true)
+            end
+          end
+
+          @url_helpers_module.module_eval do
+            redefine_method(url_name) do |*args|
+              helper.call(self, args, false)
+            end
+          end
+
+          @path_helpers << path_name
+          @url_helpers << url_name
+
+          self
+        end
+
         class UrlHelper
           def self.create(route, options, route_name, url_strategy)
             if optimize_helper?(route)
@@ -172,6 +198,16 @@ module ActionDispatch
               if args.size == arg_size && !inner_options && optimize_routes_generation?(t)
                 options = t.url_options.merge @options
                 options[:path] = optimized_helper(args)
+
+                original_script_name = options.delete(:original_script_name)
+                script_name = t._routes.find_script_name(options)
+
+                if original_script_name
+                  script_name = original_script_name + script_name
+                end
+
+                options[:script_name] = script_name
+
                 url_strategy.call options
               else
                 super
@@ -180,40 +216,40 @@ module ActionDispatch
 
             private
 
-            def optimized_helper(args)
-              params = parameterize_args(args) do
-                raise_generation_error(args)
-              end
+              def optimized_helper(args)
+                params = parameterize_args(args) do
+                  raise_generation_error(args)
+                end
 
-              @route.format params
-            end
+                @route.format params
+              end
 
-            def optimize_routes_generation?(t)
-              t.send(:optimize_routes_generation?)
-            end
+              def optimize_routes_generation?(t)
+                t.send(:optimize_routes_generation?)
+              end
 
-            def parameterize_args(args)
-              params = {}
-              @arg_size.times { |i|
-                key = @required_parts[i]
-                value = args[i].to_param
-                yield key if value.nil? || value.empty?
-                params[key] = value
-              }
-              params
-            end
+              def parameterize_args(args)
+                params = {}
+                @arg_size.times { |i|
+                  key = @required_parts[i]
+                  value = args[i].to_param
+                  yield key if value.nil? || value.empty?
+                  params[key] = value
+                }
+                params
+              end
 
-            def raise_generation_error(args)
-              missing_keys = []
-              params = parameterize_args(args) { |missing_key|
-                missing_keys << missing_key
-              }
-              constraints = Hash[@route.requirements.merge(params).sort_by{|k,v| k.to_s}]
-              message = "No route matches #{constraints.inspect}"
-              message << " missing required keys: #{missing_keys.sort.inspect}"
+              def raise_generation_error(args)
+                missing_keys = []
+                params = parameterize_args(args) { |missing_key|
+                  missing_keys << missing_key
+                }
+                constraints = Hash[@route.requirements.merge(params).sort_by { |k, v| k.to_s }]
+                message = +"No route matches #{constraints.inspect}"
+                message << ", missing required keys: #{missing_keys.sort.inspect}"
 
-              raise ActionController::UrlGenerationError, message
-            end
+                raise ActionController::UrlGenerationError, message
+              end
           end
 
           def initialize(route, options, route_name, url_strategy)
@@ -248,6 +284,8 @@ module ActionDispatch
               if args.size < path_params_size
                 path_params -= controller_options.keys
                 path_params -= result.keys
+              else
+                path_params = path_params.dup
               end
               inner_options.each_key do |key|
                 path_params.delete(key)
@@ -264,53 +302,50 @@ module ActionDispatch
         end
 
         private
-        # Create a url helper allowing ordered parameters to be associated
-        # with corresponding dynamic segments, so you can do:
-        #
-        #   foo_url(bar, baz, bang)
-        #
-        # Instead of:
-        #
-        #   foo_url(bar: bar, baz: baz, bang: bang)
-        #
-        # Also allow options hash, so you can do:
-        #
-        #   foo_url(bar, baz, bang, sort_by: 'baz')
-        #
-        def define_url_helper(mod, route, name, opts, route_key, url_strategy)
-          helper = UrlHelper.create(route, opts, route_key, url_strategy)
-          mod.module_eval do
-            define_method(name) do |*args|
-              last = args.last
-              options = case last
-                        when Hash
-                          args.pop
-                        when ActionController::Parameters
-                          if last.permitted?
-                            args.pop.to_h
-                          else
-                            raise ArgumentError, "Generating a URL from non sanitized request parameters is insecure!"
-                          end
-                        end
-              helper.call self, args, options
+          # Create a URL helper allowing ordered parameters to be associated
+          # with corresponding dynamic segments, so you can do:
+          #
+          #   foo_url(bar, baz, bang)
+          #
+          # Instead of:
+          #
+          #   foo_url(bar: bar, baz: baz, bang: bang)
+          #
+          # Also allow options hash, so you can do:
+          #
+          #   foo_url(bar, baz, bang, sort_by: 'baz')
+          #
+          def define_url_helper(mod, route, name, opts, route_key, url_strategy)
+            helper = UrlHelper.create(route, opts, route_key, url_strategy)
+            mod.module_eval do
+              define_method(name) do |*args|
+                last = args.last
+                options = \
+                  case last
+                  when Hash
+                    args.pop
+                  when ActionController::Parameters
+                    args.pop.to_h
+                  end
+                helper.call self, args, options
+              end
             end
           end
-        end
       end
 
-      # strategy for building urls to send to the client
+      # strategy for building URLs to send to the client
       PATH    = ->(options) { ActionDispatch::Http::URL.path_for(options) }
       UNKNOWN = ->(options) { ActionDispatch::Http::URL.url_for(options) }
 
       attr_accessor :formatter, :set, :named_routes, :default_scope, :router
       attr_accessor :disable_clear_and_finalize, :resources_path_names
       attr_accessor :default_url_options
-      attr_reader :env_key
+      attr_reader :env_key, :polymorphic_mappings
 
       alias :routes :set
 
       def self.default_resources_path_names
-        { :new => 'new', :edit => 'edit' }
+        { new: "new", edit: "edit" }
       end
 
       def self.new_with_config(config)
@@ -342,11 +377,18 @@ module ActionDispatch
         @prepend                    = []
         @disable_clear_and_finalize = false
         @finalized                  = false
-        @env_key                    = "ROUTES_#{object_id}_SCRIPT_NAME".freeze
+        @env_key                    = "ROUTES_#{object_id}_SCRIPT_NAME"
 
         @set    = Journey::Routes.new
         @router = Journey::Router.new @set
         @formatter = Journey::Formatter.new self
+        @polymorphic_mappings = {}
+      end
+
+      def eager_load!
+        router.eager_load!
+        routes.each(&:eager_load!)
+        nil
       end
 
       def relative_url_root
@@ -402,6 +444,7 @@ module ActionDispatch
         named_routes.clear
         set.clear
         formatter.clear
+        @polymorphic_mappings.clear
         @prepend.each { |blk| eval_block(blk) }
       end
 
@@ -418,7 +461,7 @@ module ActionDispatch
         MountedHelpers
       end
 
-      def define_mounted_helper(name)
+      def define_mounted_helper(name, script_namer = nil)
         return if MountedHelpers.method_defined?(name)
 
         routes = self
@@ -426,7 +469,7 @@ module ActionDispatch
 
         MountedHelpers.class_eval do
           define_method "_#{name}" do
-            RoutesProxy.new(routes, _routes_context, helpers)
+            RoutesProxy.new(routes, _routes_context, helpers, script_namer)
           end
         end
 
@@ -446,17 +489,50 @@ module ActionDispatch
 
           # Define url_for in the singleton level so one can do:
           # Rails.application.routes.url_helpers.url_for(args)
-          @_routes = routes
+          proxy_class = Class.new do
+            include UrlFor
+            include routes.named_routes.path_helpers_module
+            include routes.named_routes.url_helpers_module
+
+            attr_reader :_routes
+
+            def initialize(routes)
+              @_routes = routes
+            end
+
+            def optimize_routes_generation?
+              @_routes.optimize_routes_generation?
+            end
+          end
+
+          @_proxy = proxy_class.new(routes)
+
           class << self
             def url_for(options)
-              @_routes.url_for(options)
+              @_proxy.url_for(options)
+            end
+
+            def full_url_for(options)
+              @_proxy.full_url_for(options)
+            end
+
+            def route_for(name, *args)
+              @_proxy.route_for(name, *args)
             end
 
             def optimize_routes_generation?
-              @_routes.optimize_routes_generation?
+              @_proxy.optimize_routes_generation?
             end
 
-            attr_reader :_routes
+            def polymorphic_url(record_or_hash_or_array, options = {})
+              @_proxy.polymorphic_url(record_or_hash_or_array, options)
+            end
+
+            def polymorphic_path(record_or_hash_or_array, options = {})
+              @_proxy.polymorphic_path(record_or_hash_or_array, options)
+            end
+
+            def _routes; @_proxy._routes; end
             def url_options; {}; end
           end
 
@@ -480,7 +556,7 @@ module ActionDispatch
 
           # plus a singleton class method called _routes ...
           included do
-            singleton_class.send(:redefine_method, :_routes) { routes }
+            redefine_singleton_method(:_routes) { routes }
           end
 
           # And an instance method _routes. Note that
@@ -500,7 +576,7 @@ module ActionDispatch
         routes.empty?
       end
 
-      def add_route(mapping, path_ast, name, anchor)
+      def add_route(mapping, name)
         raise ArgumentError, "Invalid route name: '#{name}'" unless name.blank? || name.to_s.match(/^[_a-z]\w*$/i)
 
         if name && named_routes[name]
@@ -508,7 +584,7 @@ module ActionDispatch
             "You may have defined two routes with the same name using the `:as` option, or " \
             "you may be overriding a route already defined by a resource with the same naming. " \
             "For the latter, you can restrict the routes created with `resources` as explained here: \n" \
-            "http://guides.rubyonrails.org/routing.html#restricting-the-routes-created"
+            "https://guides.rubyonrails.org/routing.html#restricting-the-routes-created"
         end
 
         route = @set.add_route(name, mapping)
@@ -517,20 +593,58 @@ module ActionDispatch
         if route.segment_keys.include?(:controller)
           ActiveSupport::Deprecation.warn(<<-MSG.squish)
             Using a dynamic :controller segment in a route is deprecated and
-            will be removed in Rails 5.1
+            will be removed in Rails 6.0.
           MSG
         end
 
         if route.segment_keys.include?(:action)
           ActiveSupport::Deprecation.warn(<<-MSG.squish)
             Using a dynamic :action segment in a route is deprecated and
-            will be removed in Rails 5.1
+            will be removed in Rails 6.0.
           MSG
         end
 
         route
       end
 
+      def add_polymorphic_mapping(klass, options, &block)
+        @polymorphic_mappings[klass] = CustomUrlHelper.new(klass, options, &block)
+      end
+
+      def add_url_helper(name, options, &block)
+        named_routes.add_url_helper(name, options, &block)
+      end
+
+      class CustomUrlHelper
+        attr_reader :name, :defaults, :block
+
+        def initialize(name, defaults, &block)
+          @name = name
+          @defaults = defaults
+          @block = block
+        end
+
+        def call(t, args, only_path = false)
+          options = args.extract_options!
+          url = t.full_url_for(eval_block(t, args, options))
+
+          if only_path
+            "/" + url.partition(%r{(?<!/)/(?!/)}).last
+          else
+            url
+          end
+        end
+
+        private
+          def eval_block(t, args, options)
+            t.instance_exec(*args, merge_defaults(options), &block)
+          end
+
+          def merge_defaults(options)
+            defaults ? defaults.merge(options) : options
+          end
+      end
+
       class Generator
         PARAMETERIZE = lambda do |name, value|
           if name == :controller
@@ -548,12 +662,10 @@ module ActionDispatch
           @recall      = recall
           @set         = set
 
-          normalize_recall!
           normalize_options!
           normalize_controller_action_id!
           use_relative_controller!
           normalize_controller!
-          normalize_action!
         end
 
         def controller
@@ -572,11 +684,6 @@ module ActionDispatch
           end
         end
 
-        # Set 'index' as default action for recall
-        def normalize_recall!
-          @recall[:action] ||= 'index'
-        end
-
         def normalize_options!
           # If an explicit :controller was given, always make :action explicit
           # too, so that action expiry works as expected for things like
@@ -588,12 +695,12 @@ module ActionDispatch
           # be "index", not the recalled action of "show".
 
           if options[:controller]
-            options[:action]     ||= 'index'
+            options[:action]     ||= "index"
             options[:controller]   = options[:controller].to_s
           end
 
           if options.key?(:action)
-            options[:action] = (options[:action] || 'index').to_s
+            options[:action] = (options[:action] || "index").to_s
           end
         end
 
@@ -603,8 +710,8 @@ module ActionDispatch
         # :controller, :action or :id is not found, don't pull any
         # more keys from the recall.
         def normalize_controller_action_id!
-          use_recall_for(:controller) or return
-          use_recall_for(:action) or return
+          use_recall_for(:controller) || return
+          use_recall_for(:action) || return
           use_recall_for(:id)
         end
 
@@ -612,7 +719,7 @@ module ActionDispatch
         # is specified, the controller becomes "foo/baz/bat"
         def use_relative_controller!
           if !named_route && different_controller? && !controller.start_with?("/")
-            old_parts = current_controller.split('/')
+            old_parts = current_controller.split("/")
             size = controller.count("/") + 1
             parts = old_parts[0...-size] << controller
             @options[:controller] = parts.join("/")
@@ -622,7 +729,7 @@ module ActionDispatch
         # Remove leading slashes from controllers
         def normalize_controller!
           if controller
-            if controller.start_with?("/".freeze)
+            if controller.start_with?("/")
               @options[:controller] = controller[1..-1]
             else
               @options[:controller] = controller
@@ -630,13 +737,6 @@ module ActionDispatch
           end
         end
 
-        # Move 'index' action from options to recall
-        def normalize_action!
-          if @options[:action] == 'index'.freeze
-            @recall[:action] = @options.delete(:action)
-          end
-        end
-
         # Generates a path from routes, returns [path, params].
         # If no route is generated the formatter will raise ActionController::UrlGenerationError
         def generate
@@ -660,11 +760,11 @@ module ActionDispatch
 
       # Generate the path indicated by the arguments, and return an array of
       # the keys that were not used to generate it.
-      def extra_keys(options, recall={})
+      def extra_keys(options, recall = {})
         generate_extras(options, recall).last
       end
 
-      def generate_extras(options, recall={})
+      def generate_extras(options, recall = {})
         route_key = options.delete :use_route
         path, params = generate(route_key, options, recall)
         return path, params.keys
@@ -684,7 +784,7 @@ module ActionDispatch
       end
 
       def find_script_name(options)
-        options.delete(:script_name) || find_relative_url_root(options) || ''
+        options.delete(:script_name) || find_relative_url_root(options) || ""
       end
 
       def find_relative_url_root(options)
@@ -706,7 +806,7 @@ module ActionDispatch
           password = options.delete :password
         end
 
-        recall  = options.delete(:_recall) { {} }
+        recall = options.delete(:_recall) { {} }
 
         original_script_name = options.delete(:original_script_name)
         script_name = find_script_name options
@@ -745,12 +845,16 @@ module ActionDispatch
         extras = environment[:extras] || {}
 
         begin
-          env = Rack::MockRequest.env_for(path, {:method => method})
+          env = Rack::MockRequest.env_for(path, method: method)
         rescue URI::InvalidURIError => e
           raise ActionController::RoutingError, e.message
         end
 
         req = make_request(env)
+        recognize_path_with_request(req, path, extras)
+      end
+
+      def recognize_path_with_request(req, path, extras, raise_on_missing: true)
         @router.recognize(req) do |route, params|
           params.merge!(extras)
           params.each do |key, value|
@@ -759,8 +863,7 @@ module ActionDispatch
               params[key] = URI.parser.unescape(value)
             end
           end
-          old_params = req.path_parameters
-          req.path_parameters = old_params.merge params
+          req.path_parameters = params
           app = route.app
           if app.matches?(req) && app.dispatcher?
             begin
@@ -770,10 +873,15 @@ module ActionDispatch
             end
 
             return req.path_parameters
+          elsif app.matches?(req) && app.engine?
+            path_parameters = app.rack_app.routes.recognize_path_with_request(req, path, extras, raise_on_missing: false)
+            return path_parameters if path_parameters
           end
         end
 
-        raise ActionController::RoutingError, "No route matches #{path.inspect}"
+        if raise_on_missing
+          raise ActionController::RoutingError, "No route matches #{path.inspect}"
+        end
       end
     end
     # :startdoc:
diff --git a/actionpack/lib/action_dispatch/routing/routes_proxy.rb b/actionpack/lib/action_dispatch/routing/routes_proxy.rb
index 040ea04046..587a72729c 100644
--- a/actionpack/lib/action_dispatch/routing/routes_proxy.rb
+++ b/actionpack/lib/action_dispatch/routing/routes_proxy.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/array/extract_options'
+# frozen_string_literal: true
+
+require "active_support/core_ext/array/extract_options"
 
 module ActionDispatch
   module Routing
@@ -8,9 +10,10 @@ module ActionDispatch
       attr_accessor :scope, :routes
       alias :_routes :routes
 
-      def initialize(routes, scope, helpers)
+      def initialize(routes, scope, helpers, script_namer = nil)
         @routes, @scope = routes, scope
         @helpers = helpers
+        @script_namer = script_namer
       end
 
       def url_options
@@ -19,7 +22,8 @@ module ActionDispatch
         end
       end
 
-      def respond_to?(method, include_private = false)
+    private
+      def respond_to_missing?(method, _)
         super || @helpers.respond_to?(method)
       end
 
@@ -28,15 +32,38 @@ module ActionDispatch
           self.class.class_eval <<-RUBY, __FILE__, __LINE__ + 1
             def #{method}(*args)
               options = args.extract_options!
-              args << url_options.merge((options || {}).symbolize_keys)
+              options = url_options.merge((options || {}).symbolize_keys)
+
+              if @script_namer
+                options[:script_name] = merge_script_names(
+                  options[:script_name],
+                  @script_namer.call(options)
+                )
+              end
+
+              args << options
               @helpers.#{method}(*args)
             end
           RUBY
-          send(method, *args)
+          public_send(method, *args)
         else
           super
         end
       end
+
+      # Keeps the part of the script name provided by the global
+      # context via ENV["SCRIPT_NAME"], which `mount` doesn't know
+      # about since it depends on the specific request, but use our
+      # script name resolver for the mount point dependent part.
+      def merge_script_names(previous_script_name, new_script_name)
+        return new_script_name unless previous_script_name
+
+        resolved_parts = new_script_name.count("/")
+        previous_parts = previous_script_name.count("/")
+        context_parts = previous_parts - resolved_parts + 1
+
+        (previous_script_name.split("/").slice(0, context_parts).join("/")) + new_script_name
+      end
     end
   end
 end
diff --git a/actionpack/lib/action_dispatch/routing/url_for.rb b/actionpack/lib/action_dispatch/routing/url_for.rb
index 28be189f93..fcb8ae296b 100644
--- a/actionpack/lib/action_dispatch/routing/url_for.rb
+++ b/actionpack/lib/action_dispatch/routing/url_for.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActionDispatch
   module Routing
     # In <tt>config/routes.rb</tt> you define URL-to-controller mappings, but the reverse
@@ -107,16 +109,16 @@ module ActionDispatch
       end
 
       # Hook overridden in controller to add request information
-      # with `default_url_options`. Application logic should not
+      # with +default_url_options+. Application logic should not
       # go into url_options.
       def url_options
         default_url_options
       end
 
-      # Generate a url based on the options provided, default_url_options and the
+      # Generate a URL based on the options provided, default_url_options and the
       # routes defined in routes.rb. The following options are supported:
       #
-      # * <tt>:only_path</tt> - If true, the relative url is returned. Defaults to +false+.
+      # * <tt>:only_path</tt> - If true, the relative URL is returned. Defaults to +false+.
       # * <tt>:protocol</tt> - The protocol to connect to. Defaults to 'http'.
       # * <tt>:host</tt> - Specifies the host the link should be targeted at.
       #   If <tt>:only_path</tt> is false, this option must be
@@ -131,6 +133,7 @@ module ActionDispatch
       #   <tt>ActionDispatch::Http::URL.tld_length</tt>, which in turn defaults to 1.
       # * <tt>:port</tt> - Optionally specify the port to connect to.
       # * <tt>:anchor</tt> - An anchor name to be appended to the path.
+      # * <tt>:params</tt> - The query parameters to be appended to the path.
       # * <tt>:trailing_slash</tt> - If true, adds a trailing slash, as in "/archive/2009/"
       # * <tt>:script_name</tt> - Specifies application path relative to domain root. If provided, prepends application path.
       #
@@ -153,7 +156,7 @@ module ActionDispatch
       # Missing routes keys may be filled in from the current request's parameters
       # (e.g. +:controller+, +:action+, +:id+ and any other parameters that are
       # placed in the path). Given that the current action has been reached
-      # through `GET /users/1`:
+      # through <tt>GET /users/1</tt>:
       #
       #   url_for(only_path: true)                        # => '/users/1'
       #   url_for(only_path: true, action: 'edit')        # => '/users/1/edit'
@@ -164,20 +167,17 @@ module ActionDispatch
       # implicitly used by +url_for+ can always be overwritten like shown on the
       # last +url_for+ calls.
       def url_for(options = nil)
+        full_url_for(options)
+      end
+
+      def full_url_for(options = nil) # :nodoc:
         case options
         when nil
           _routes.url_for(url_options.symbolize_keys)
-        when Hash
-          route_name = options.delete :use_route
-          _routes.url_for(options.symbolize_keys.reverse_merge!(url_options),
-                         route_name)
-        when ActionController::Parameters
-          unless options.permitted?
-            raise ArgumentError.new("Generating a URL from non sanitized request parameters is insecure!")
-          end
+        when Hash, ActionController::Parameters
           route_name = options.delete :use_route
-          _routes.url_for(options.to_h.symbolize_keys.
-                          reverse_merge!(url_options), route_name)
+          merged_url_options = options.to_h.symbolize_keys.reverse_merge!(url_options)
+          _routes.url_for(merged_url_options, route_name)
         when String
           options
         when Symbol
@@ -192,22 +192,46 @@ module ActionDispatch
         end
       end
 
+      # Allows calling direct or regular named route.
+      #
+      #   resources :buckets
+      #
+      #   direct :recordable do |recording|
+      #     route_for(:bucket, recording.bucket)
+      #   end
+      #
+      #   direct :threadable do |threadable|
+      #     route_for(:recordable, threadable.parent)
+      #   end
+      #
+      # This maintains the context of the original caller on
+      # whether to return a path or full URL, e.g:
+      #
+      #   threadable_path(threadable)  # => "/buckets/1"
+      #   threadable_url(threadable)   # => "http://example.com/buckets/1"
+      #
+      def route_for(name, *args)
+        public_send(:"#{name}_url", *args)
+      end
+
       protected
 
-      def optimize_routes_generation?
-        _routes.optimize_routes_generation? && default_url_options.empty?
-      end
+        def optimize_routes_generation?
+          _routes.optimize_routes_generation? && default_url_options.empty?
+        end
 
-      def _with_routes(routes)
-        old_routes, @_routes = @_routes, routes
-        yield
-      ensure
-        @_routes = old_routes
-      end
+      private
 
-      def _routes_context
-        self
-      end
+        def _with_routes(routes) # :doc:
+          old_routes, @_routes = @_routes, routes
+          yield
+        ensure
+          @_routes = old_routes
+        end
+
+        def _routes_context # :doc:
+          self
+        end
     end
   end
 end