bug #36497 [Filesystem] Handle paths on different drives (crishoj)

This PR was squashed before being merged into the 3.4 branch.

Discussion
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[Filesystem] Handle paths on different drives

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| License       | MIT

`makePathRelative` strips and ignores the drive letters given Windows paths on different drives, resulting in a relative path which does not resolve to the desired target.

This PR makes `makePathRelative` notice paths on different drives, and return the full (absolute) target path in case instead.

Commits
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00e727a [Filesystem] Handle paths on different drives

src/Symfony/Component/Filesystem/Filesystem.php

@@ -455,37 +455,36 @@ public function makePathRelative($endPath, $startPath)
             $startPath = str_replace('\\', '/', $startPath);
         }
 
-        $stripDriveLetter = function ($path) {
-            if (\strlen($path) > 2 && ':' === $path[1] && '/' === $path[2] && ctype_alpha($path[0])) {
-                return substr($path, 2);
-            }
-
-            return $path;
+        $splitDriveLetter = function ($path) {
+            return (\strlen($path) > 2 && ':' === $path[1] && '/' === $path[2] && ctype_alpha($path[0]))
+                ? [substr($path, 2), strtoupper($path[0])]
+                : [$path, null];
         };
 
-        $endPath = $stripDriveLetter($endPath);
-        $startPath = $stripDriveLetter($startPath);
-
-        // Split the paths into arrays
-        $startPathArr = explode('/', trim($startPath, '/'));
-        $endPathArr = explode('/', trim($endPath, '/'));
-
-        $normalizePathArray = function ($pathSegments, $absolute) {
+        $splitPath = function ($path, $absolute) {
             $result = [];
 
-            foreach ($pathSegments as $segment) {
+            foreach (explode('/', trim($path, '/')) as $segment) {
                 if ('..' === $segment && ($absolute || \count($result))) {
                     array_pop($result);
-                } elseif ('.' !== $segment) {
+                } elseif ('.' !== $segment && '' !== $segment) {
                     $result[] = $segment;
                 }
             }
 
             return $result;
         };
 
-        $startPathArr = $normalizePathArray($startPathArr, static::isAbsolutePath($startPath));
-        $endPathArr = $normalizePathArray($endPathArr, static::isAbsolutePath($endPath));
+        list($endPath, $endDriveLetter) = $splitDriveLetter($endPath);
+        list($startPath, $startDriveLetter) = $splitDriveLetter($startPath);
+
+        $startPathArr = $splitPath($startPath, static::isAbsolutePath($startPath));
+        $endPathArr = $splitPath($endPath, static::isAbsolutePath($endPath));
+
+        if ($endDriveLetter && $startDriveLetter && $endDriveLetter != $startDriveLetter) {
+            // End path is on another drive, so no relative path exists
+            return $endDriveLetter.':/'.($endPathArr ? implode('/', $endPathArr).'/' : '');
+        }
 
         // Find for which directory the common path stops
         $index = 0;

src/Symfony/Component/Filesystem/Tests/FilesystemTest.php

@@ -1111,10 +1111,14 @@ public function providePathsForMakePathRelative()
             ['/../aa/bb/cc', '/aa/dd/..', 'bb/cc/'],
             ['/../../aa/../bb/cc', '/aa/dd/..', '../bb/cc/'],
             ['C:/aa/bb/cc', 'C:/aa/dd/..', 'bb/cc/'],
+            ['C:/aa/bb/cc', 'c:/aa/dd/..', 'bb/cc/'],
             ['c:/aa/../bb/cc', 'c:/aa/dd/..', '../bb/cc/'],
             ['C:/aa/bb/../../cc', 'C:/aa/../dd/..', 'cc/'],
             ['C:/../aa/bb/cc', 'C:/aa/dd/..', 'bb/cc/'],
             ['C:/../../aa/../bb/cc', 'C:/aa/dd/..', '../bb/cc/'],
+            ['D:/', 'C:/aa/../bb/cc', 'D:/'],
+            ['D:/aa/bb', 'C:/aa', 'D:/aa/bb/'],
+            ['D:/../../aa/../bb/cc', 'C:/aa/dd/..', 'D:/bb/cc/'],
         ];
 
         if ('\\' === \DIRECTORY_SEPARATOR) {