Only enable routing source locations when using routes command

The overhead isn't necessary for development when not using the routes
command. We can omit it entirely by checking for existence of the routes
command constant.

actionpack/lib/action_dispatch/railtie.rb

@@ -68,8 +68,6 @@ class Railtie < Rails::Railtie # :nodoc:
       config.action_dispatch.always_write_cookie = Rails.env.development? if config.action_dispatch.always_write_cookie.nil?
       ActionDispatch::Cookies::CookieJar.always_write_cookie = config.action_dispatch.always_write_cookie
 
-      ActionDispatch::Routing::Mapper.route_source_locations = Rails.env.development?
-
       ActionDispatch::Http::Cache::Request.strict_freshness = app.config.action_dispatch.strict_freshness
       ActionDispatch.test_app = app
     end

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -6,6 +6,7 @@
 require "active_support/core_ext/enumerable"
 require "active_support/core_ext/array/extract_options"
 require "active_support/core_ext/regexp"
+require "action_dispatch/routing"
 require "action_dispatch/routing/redirection"
 require "action_dispatch/routing/endpoint"
 

railties/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Enable tracking route source locations only when using routes command. Previously,
+    it was enabled in development mode, but is only needed for `bin/rails routes -E`.
+
+    *Gannon McGibbon*
+
 *   Deprecate `bin/rake stats` in favor of `bin/rails stats`.
 
     *Juan Vásquez*

railties/lib/rails/commands/routes/routes_command.rb

@@ -22,6 +22,8 @@ def invoke_command(*)
 
       desc "routes", "List all the defined routes"
       def perform(*)
+        require "action_dispatch/routing/mapper"
+        ActionDispatch::Routing::Mapper.route_source_locations = true
         boot_application!
         require "action_dispatch/routing/inspector"
 

railties/test/commands/routes_test.rb

@@ -403,6 +403,12 @@ class Rails::Command::RoutesTest < ActiveSupport::TestCase
     assert_includes(output, "No unused routes found.")
   end
 
+  test "route source locations aren't included when booted normally" do
+    output = rails "runner", "print !!ActionDispatch::Routing::Mapper.route_source_locations"
+
+    assert_equal("false", output)
+  end
+
   private
     def run_routes_command(args = [])
       rails "routes", args