vfs: directory created during unit tests

This makes sense to me. I think it looks good to go, just a few nits:

1. +++ b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
   @@ -149,8 +149,18 @@ protected function createDirectory($directory, $mode = 0777) {
   +    if ($scheme && "$scheme:" == $parent) {
   +      $parent_exists = TRUE; // We can't go deeper so it "exists"
   

   Nit: should this use ===?

2. +++ b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
   @@ -149,8 +149,18 @@ protected function createDirectory($directory, $mode = 0777) {
   +      $parent_exists = TRUE; // We can't go deeper so it "exists"
   

   Nit: This should be above the code line, and end in an '.' I think...

I was trying to manually reproduce this issue. I ran vendor/bin/phpunit -c core/phpunit.xml core/tests/Drupal/Tests/Core/File/ but no vfs: directory is created in the root directory...

Ok, confirmed that running the entire test suite creates the vfs: directory. Also confirmed the tests in this patch fail (the directory is created) without the corresponding fix. Given that, I think this looks good to go.

Given this is extremely low level code I'd like to make this change in the smallest possible performance impact as possible.

Can I suggest we change the patch to do:

    // If the parent directory doesn't exist, try to create it.
    $parent_exists = is_dir($parent = dirname($directory));
    if (!$parent_exists) {
      // Check if this is the root of some sort of stream. dirname() will strip
      // the trailing slashes from the uri leaving the scheme and a colon so we
      // use that for our comparison.
      $scheme = parse_url($directory, PHP_URL_SCHEME);
      if ($scheme && "$scheme:" === $parent) {
        // We can't go any higher so it "exists" and we'll let the stream sort it
        // out.
        $parent_exists = TRUE;
      }
      else {
        $parent_exists = $this->createDirectory($parent, $mode);
      }
    }

That way we only parse the URL when the directory doesn't exist which is the only time we actually need to.

And maybe we should consider doing something to not have to parse the directory all the times during a recursive call. Note this method is called a lot during a twig file cache rebuild.

  /**
   * Ensures the requested directory exists and has the right permissions.
   *
   * For compatibility with open_basedir, the requested directory is created
   * using a recursion logic that is based on the relative directory path/tree:
   * It works from the end of the path recursively back towards the root
   * directory, until an existing parent directory is found. From there, the
   * subdirectories are created.
   *
   * @param string $directory
   *   The directory path.
   * @param int $mode
   *   The mode, permissions, the directory should have.
   * @param string $scheme
   *   Used during recursive calls. Do not set.
   *
   * @return bool
   *   TRUE if the directory exists or has been created, FALSE otherwise.
   */
  protected function createDirectory($directory, $mode = 0777, $scheme = NULL) {
    // If the directory exists already, there's nothing to do.
    if (is_dir($directory)) {
      return TRUE;
    }

    // If the parent directory doesn't exist, try to create it.
    $parent_exists = is_dir($parent = dirname($directory));
    if (!$parent_exists) {
      if ($scheme === NULL) {
        $scheme = (string) parse_url($directory, PHP_URL_SCHEME);
      }
      // Check if this is the root of some sort of stream. dirname() will strip
      // the trailing slashes from the uri leaving the scheme and a colon so we
      // use that for our comparison.
      if ($scheme && "$scheme:" === $parent) {
        // We can't go any higher so it "exists" and we'll let the stream sort it
        // out.
        $parent_exists = TRUE;
      }
      else {
        $parent_exists = $this->createDirectory($parent, $mode, $scheme);
      }
    }

    // If parent exists, try to create the directory and ensure to set its
    // permissions, because mkdir() obeys the umask of the current process.
    if ($parent_exists) {
      // We hide warnings and ignore the return because there may have been a
      // race getting here and the directory could already exist.
      @mkdir($directory);
      // Only try to chmod() if the subdirectory could be created.
      if (is_dir($directory)) {
        // Avoid writing permissions if possible.
        if (fileperms($directory) !== $mode) {
          return chmod($directory, $mode);
        }
        return TRUE;
      }
      else {
        // Something failed and the directory doesn't exist.
        trigger_error('mkdir(): Permission Denied', E_USER_WARNING);
      }
    }
    return FALSE;
  }