feature #13264 URL manipulations as a Twig extension (fabpot)

This PR was merged into the 2.7 branch.

Discussion
----------

URL manipulations as a Twig extension

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | symfony/symfony-docs#4805

While working on the new asset component, I realized that the "absolute URL" feature was misplaced and would benefit from being exposed as a Twig function (composition is always a good thing). Then, I wondered if having a Twig function to generate a relative path (like done by the Routing component would also make sense). And here is the corresponding PR.

```jinja
{# generate an absolute URL for the given absolute path #}
{{ absolute_url('/me.png') }}

{# generate a relative path for the given absolute path (based on the current Request) #}
{{ relative_path('/foo/me.png') }}

{# compose as you see fit #}
{{ absolute_url(asset('me.png')) }}
```

As you can see, we require an absolute path for both functions (and we even add the leading slash if it is omitted), not sure if we want to do otherwise.

ping @Tobion

Commits
-------

0ec852d added a relative_path Twig function
ee27ed8 added an absolute_url() Twig function

Request.php

@@ -1137,6 +1137,61 @@ public function getUriForPath($path)
         return $this->getSchemeAndHttpHost().$this->getBaseUrl().$path;
     }
 
+    /**
+     * Returns the path as relative reference from the current Request path.
+     *
+     * Only the URIs path component (no schema, host etc.) is relevant and must be given.
+     * Both paths must be absolute and not contain relative parts.
+     * Relative URLs from one resource to another are useful when generating self-contained downloadable document archives.
+     * Furthermore, they can be used to reduce the link size in documents.
+     *
+     * Example target paths, given a base path of "/a/b/c/d":
+     * - "/a/b/c/d"     -> ""
+     * - "/a/b/c/"      -> "./"
+     * - "/a/b/"        -> "../"
+     * - "/a/b/c/other" -> "other"
+     * - "/a/x/y"       -> "../../x/y"
+     *
+     * @param string $path The target path
+     *
+     * @return string The relative target path
+     */
+    public function getRelativeUriForPath($path)
+    {
+        // be sure that we are dealing with an absolute path
+        if (!isset($path[0]) || '/' !== $path[0]) {
+            return $path;
+        }
+
+        if ($path === $basePath = $this->getPathInfo()) {
+            return '';
+        }
+
+        $sourceDirs = explode('/', isset($basePath[0]) && '/' === $basePath[0] ? substr($basePath, 1) : $basePath);
+        $targetDirs = explode('/', isset($path[0]) && '/' === $path[0] ? substr($path, 1) : $path);
+        array_pop($sourceDirs);
+        $targetFile = array_pop($targetDirs);
+
+        foreach ($sourceDirs as $i => $dir) {
+            if (isset($targetDirs[$i]) && $dir === $targetDirs[$i]) {
+                unset($sourceDirs[$i], $targetDirs[$i]);
+            } else {
+                break;
+            }
+        }
+
+        $targetDirs[] = $targetFile;
+        $path = str_repeat('../', count($sourceDirs)).implode('/', $targetDirs);
+
+        // A reference to the same base directory or an empty subdirectory must be prefixed with "./".
+        // This also applies to a segment with a colon character (e.g., "file:colon") that cannot be used
+        // as the first segment of a relative-path reference, as it would be mistaken for a scheme name
+        // (see http://tools.ietf.org/html/rfc3986#section-4.2).
+        return !isset($path[0]) || '/' === $path[0]
+            || false !== ($colonPos = strpos($path, ':')) && ($colonPos < ($slashPos = strpos($path, '/')) || false === $slashPos)
+            ? "./$path" : $path;
+    }
+
     /**
      * Generates the normalized query string for the Request.
      *

Tests/RequestTest.php

@@ -575,6 +575,26 @@ public function testGetUriForPath()
         $this->assertEquals('http://servername/some/path', $request->getUriForPath('/some/path'));
     }
 
+    /**
+     * @dataProvider getRelativeUriForPathData()
+     */
+    public function testGetRelativeUriForPath($expected, $pathinfo, $path)
+    {
+        $this->assertEquals($expected, Request::create($pathinfo)->getRelativeUriForPath($path));
+    }
+
+    public function getRelativeUriForPathData()
+    {
+        return array(
+            array('me.png', '/foo', '/me.png'),
+            array('../me.png', '/foo/bar', '/me.png'),
+            array('me.png', '/foo/bar', '/foo/me.png'),
+            array('../baz/me.png', '/foo/bar/b', '/foo/baz/me.png'),
+            array('../../fooz/baz/me.png', '/foo/bar/b', '/fooz/baz/me.png'),
+            array('baz/me.png', '/foo/bar/b', 'baz/me.png'),
+        );
+    }
+
     /**
      * @covers Symfony\Component\HttpFoundation\Request::getUserInfo
      */