Remove file_exists() when registering namespaces for Twig template paths

Postponed until #2291449: Add Twig template inheritance based on the theme registry, enable adding Twig loaders is committed.

Although this might cause some issues (in \Twig_Loader_Filesystem) :/

if (!is_dir($path)) {
  throw new Twig_Error_Loader(sprintf('The "%s" directory does not exist.', $path));
}

I suppose we could add our own version of addPath() that removes that :)

I suggest #3, we are already subclassing the Twig Filesystem class, we can override addPath to remove the is_dir check. As long as that has no nasty side effects it seems like the best way forward to get the performance we want.

Make sense?

I think the idea would be to just add all directories regardless of whether they exist or not, we can double check to see how Twig handles it when trying to load namespaced templates to see if it causes any issues. But right now I don't see any other way forward if we want to remove the file_exists().

Hopefully that makes sense, it's early :)

@larsmw, yes to #18 - code looks good now, thanks! Please post interdiffs when you update the patch, great habit to get into early and makes it easier to review changes. Getting patches reviewed is most often the biggest bottleneck in the issue queues so anything you can to do help make that easier is a huge win in my opinion :)

1. +++ b/core/lib/Drupal/Core/Template/Loader/FilesystemLoader.php
   @@ -43,10 +43,19 @@ public function __construct($paths = array(), ModuleHandlerInterface $module_han
   +   * @param string $path A path where to look for templates
   +   * @param string $namespace A path name
   

   These should be updated to match our documentation standards on params, whitespace and punctuation changes would be needed: https://www.drupal.org/node/1354#param

2. +++ b/core/lib/Drupal/Core/Template/Loader/FilesystemLoader.php
   @@ -43,10 +43,19 @@ public function __construct($paths = array(), ModuleHandlerInterface $module_han
   +  }
    }
   

   Minor: Missing blank line between the last method and the end of the class per https://www.drupal.org/node/608152#indenting.

It's kind of a cascade, the is_dir() will fail without the file_exists() filtering out nonexistent directories. The nonexistent directories are just being added as possible namespaces, Twig should still complain on its own when you try to extend/include/whatever a template that doesn't exist, that could use a bit of manual (or automated?) testing.

Because we have the string loader, calling a nonexistent template just prints the string, with or without the patch. So no concerns there. This also means that I'm pretty sure we don't have a good way of testing this currently (like by catching an exception) until #2369981: Not found templates are displayed literally instead of throwing an Exception due to string loader is resolved, which I just bumped to major.

Attaching one minor change to remove a now unnecessary variable. This looks good to me now as far as documentation and coding style, and solves the stated task, RTBC. I don't think this needs additional test coverage.

--

For this one profiling on an SSD is probably not the best way to test, but I was able to confirm that we are cutting down on calls to file_exists() (and is_dir()).

Scenario: Standard profile, Bartik homepage, added 17 search blocks to bring the total of search blocks up to 18. Gave anonymous users the 'search content' permission.

Reduced function calls:

file_exists(): -45
is_dir(): -25

There are 21 more calls to rtrim() with this approach, but those are extremely cheap.

=== 8.0.x..8.0.x compared (54e0a6d45fe2a..54e0a77153dbf):

ct  : 166,652|166,652|0|0.0%
wt  : 698,622|696,872|-1,750|-0.3%
cpu : 682,564|681,253|-1,311|-0.2%
mu  : 49,588,128|49,588,128|0|0.0%
pmu : 50,180,616|50,180,616|0|0.0%

http://www.lionsad.de/xhprof-kit/xhprof/xhprof_html/?run1=54e0a6d45fe2a&...

=== 8.0.x..twig-ns-file-exists-2383413-26 compared (54e0a6d45fe2a..54e0a7d2151b1):

ct  : 166,652|166,624|-28|-0.0%
wt  : 698,622|697,883|-739|-0.1%
cpu : 682,564|682,200|-364|-0.1%
mu  : 49,588,128|49,597,752|9,624|0.0%
pmu : 50,180,616|50,191,232|10,616|0.0%

http://www.lionsad.de/xhprof-kit/xhprof/xhprof_html/?run1=54e0a6d45fe2a&...