Look up route from requirements (#51850)

* Lookup route from requirements

* Add docs

* Strings instead of symbols

S

* Update actionpack/lib/action_dispatch/routing/route_set.rb

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

* Update actionpack/lib/action_dispatch/routing/route_set.rb

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

* Update actionpack/lib/action_dispatch/routing/route_set.rb

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

* Update actionpack/lib/action_dispatch/routing/route_set.rb

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

---------

Co-authored-by: Andy Waite <andyw8@users.noreply.github.com>
Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -12,8 +12,25 @@
 
 module ActionDispatch
   module Routing
-    # :stopdoc:
+    # The RouteSet contains a collection of Route instances, representing the routes
+    # typically defined in `config/routes.rb`.
     class RouteSet
+      # Returns a Route matching the given requirements, or `nil` if none are found.
+      #
+      # This is intended for use by tools such as Language Servers.
+      #
+      # Given the routes are defined as:
+      #
+      #   resources :posts
+      #
+      # Then the following will return the Route for the `show` action:
+      #
+      #   Rails.application.routes.from_requirements(controller: "posts", action: "show")
+      def from_requirements(requirements)
+        routes.find { |route| route.requirements == requirements }
+      end
+      # :stopdoc:
+
       # Since the router holds references to many parts of the system like engines,
       # controllers and the application itself, inspecting the route set can actually
       # be really slow, therefore we default alias inspect to to_s.

actionpack/test/dispatch/routing/route_set_test.rb

@@ -165,6 +165,28 @@ def call(env)
         assert_equal "/wildcard/a%0Anewline", url_helpers.wildcard_path(wildcard_segment: "a\nnewline")
       end
 
+      test "find a route for the given requirements" do
+        draw do
+          resources :foo
+          resources :bar
+        end
+
+        route = @set.from_requirements(controller: "bar", action: "index")
+
+        assert_equal "bar_index", route.name
+      end
+
+      test "find a route for the given requirements returns nil for no match" do
+        draw do
+          resources :foo
+          resources :bar
+        end
+
+        route = @set.from_requirements(controller: "baz", action: "index")
+
+        assert_nil route
+      end
+
       private
         def draw(&block)
           @set.draw(&block)