bug #11970 [Finder] Escape location for regex searches (ymc-dabe)

This PR was squashed before being merged into the 2.3 branch (closes #11970).

Discussion
----------

[Finder] Escape location for regex searches

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

If the location to start searching in contains a regex special char
like + or ? and the path restriction is a regular expresion with a start
limitation. No results will be found wtih at least GnuFindAdapter - e.g.:
```
use Symfony\Component\Finder\Finder;
use Symfony\Component\Finder\Adapter;

mkdir('/tmp/reg+ex/dir/subdir', 0777, true);

$finder = Finder::create()
    ->removeAdapters()
    ->addAdapter(new Adapter\GnuFindAdapter());
$finder->in('/tmp/reg+ex')->path('/^dir/');

print count($finder)."\n";
```

Expected result: 2
Actual result is: 0

This pull request consists of:
* a new test checking for this bug (0e81086a49425d0e12cff4f479fabeb97e9ed757)
* the actual fix (6595b6b2b71afc57ef08686b4584713c0e4e48ed)
* changes to comply with the coding standard (7f199c5b53b3c1f38b36dcc286d3b20ae877425b)

## How to reproduce
### Fastest way
1. Move or copy your local symfony clone into a location containing special regex chars:
  * `mv symfony symfony+regex`
2. Run tests in there
  * `cd symfony+regex && phpunit`

> Result: Some tests in the finder component will fail.

### Alternative: A new clone
1. Clone symfony in a directory containing at least one regex special char
  * `git clone https://github.com/symfony/symfony.git /tmp/symfony+regexchar`
2. As usual get composer, install dependencies and get phpunit
  * You might simply want to follow [this guide](http://symfony.com/doc/current/contributing/code/tests.html)
3. Run tests in there
   * `cd /tmp/symfony+regexchar && phpunit`

> Result: Some tests in the finder component will fail.

### Alternative: Apply the new test
1. Apply commit a29d1207ced2949c918357cf271200523960caef to your symfony clone
2. Run tests

> Result: The new test will fail.

Commits
-------

b63926b [Finder] Escape location for regex searches

src/Symfony/Component/Finder/Adapter/AbstractFindAdapter.php

@@ -216,7 +216,7 @@ abstract class AbstractFindAdapter extends AbstractAdapter
             // Fixes 'not search' regex problems.
             if ($expr->isRegex()) {
                 $regex = $expr->getRegex();
-                $regex->prepend($regex->hasStartFlag() ? $dir.DIRECTORY_SEPARATOR : '.*')->setEndJoker(!$regex->hasEndFlag());
+                $regex->prepend($regex->hasStartFlag() ? preg_quote($dir).DIRECTORY_SEPARATOR : '.*')->setEndJoker(!$regex->hasEndFlag());
             } else {
                 $expr->prepend('*')->append('*');
             }

src/Symfony/Component/Finder/Tests/FinderTest.php

@@ -569,6 +569,20 @@ class FinderTest extends Iterator\RealIteratorTestCase
         }
     }
 
+    /**
+     * @dataProvider getAdaptersTestData
+     */
+    public function testRegexSpecialCharsLocationWithPathRestrictionContainingStartFlag(Adapter\AdapterInterface $adapter)
+    {
+        $finder = $this->buildFinder($adapter);
+        $finder->in(__DIR__.DIRECTORY_SEPARATOR.'Fixtures'.DIRECTORY_SEPARATOR.'r+e.g?e*x[c]a(r)s')
+            ->path('/^dir/');
+
+        $expected = array('r+e.g?e*x[c]a(r)s'.DIRECTORY_SEPARATOR.'dir',
+                          'r+e.g?e*x[c]a(r)s'.DIRECTORY_SEPARATOR.'dir'.DIRECTORY_SEPARATOR.'bar.dat',);
+        $this->assertIterator($this->toAbsoluteFixtures($expected), $finder);
+    }
+
     public function testAdaptersOrdering()
     {
         $finder = Finder::create()