Make (routing by path) cacheable

@dawehner, this might be handy: https://twitter.com/andrei_mateescu/status/344855495967928320 :)

I believe we need tests here.

See #643984: Cache menu_get_item() and #1234830: Revert cache_menu patch removal, add a $conf setting instead (was: cache_menu: huge table size).

Short version - this is an absolute necessity to keep some sites up (MySQL query cache saved by memcache), but it can also take other sites down (cache table size growing out of control using MySQL for the cache).

On the 7.x issue we were discussing making it configurable.

For 8.x I'm wondering if we want a special cache bin that requires a size-limited cache backend, but otherwise uses the null or memory cache backend if one isn't available.

Menu items never had a menu_get_item() to load the route - the route was loaded with the menu links as part of the database query via join. This is part of the reason Drupal 8 routing is so much slower for menu link rendering. See for example #1845402-5: Update menu link access checks for new router for a slightly longer description of the regression.

So while there can be other menu_get_item() calls with a path name in 7.x, nearly all of them were for the incoming request not for link generation.

The issue here is that there can be potentially millions of valid paths on a site (nodes + users + $entity_type), and if the site is being crawled that will fill the cache quite quickly. Also the original patch that went in had this as a permanent cache entry (since it's valid until the router changes).

I would totally RTBC this, it looks great!

1. +++ b/core/core.services.yml
   @@ -520,6 +522,12 @@ services:
   +  router.cached:
   +    class: Drupal\Core\Routing\CachedUrlMatcher
   

   The service or class name should be more consistent?

2. +++ b/core/lib/Drupal/Core/Access/AccessManager.php
   @@ -221,5 +229,19 @@ protected function performCheck($service_id, ArgumentsResolverInterface $argumen
   +  public function setUrlMatcher(UrlMatcherInterface $url_matcher) {
   +    $this->urlMatcher = $url_matcher;
   +
   +    return $this;
   +  }
   

   Missing documentation - looks like it should be on the interface.

3. It would be great if the issue summary could be updated to have the plan going forward as this patch adds lots of code that is unused atm

4. +++ b/core/lib/Drupal/Core/Routing/RouteProvider.php
   @@ -71,10 +79,11 @@ class RouteProvider implements RouteProviderInterface, PagedRouteProviderInterfa
   +  public function __construct(Connection $connection, RouteBuilderInterface $route_builder, StateInterface $state, CacheBackendInterface $cache_backend, $table = 'router') {
   
   @@ -276,6 +285,9 @@ public function getRoutesByPattern($pattern) {
   +    if ($cache = $this->cacheBackend->get('routing_by_path:' . $path)) {
   +      return $cache->data;
   +    }
   
   @@ -301,6 +313,8 @@ protected function getRoutesByPath($path) {
   +    $this->cacheBackend->set('routing_by_path:' . $path, $collection);
   

   Currently this will result in just shoving stuff in memory that is never used. How caching if a cache backend is injected and defaulting to the backend to NULL.

BE in IS is not complete and one minor nit. I think it is ready.

+++ b/sites/default/default.settings.php
@@ -390,6 +390,30 @@
+// Per default cache the menu and routing just in memory. Given that there a lot
+// of possible allowed paths you should better use a cache backend, which has
+// a limited total size / limited amount of items. Database cache would
+// potentially fill up a lot.

I think line commenting is wrong here we should use block commenting.

Fixes editable config test failure.

Fix more editable config fails.

A file has been deleted that shouldn't be deleted ;)

Whoops!

Patch requires re-roll - setting to needs work.