[BUGFIX] Do not try to create symlinks on Windows

When a junction already exists on Windows, it is tried
to create a symlink, because of a missing OS check.

While this works as errors are ignored, it is
an unnecessary filesystem call.

Therefore the code is changed to only emit
the appropriate filesystem operations per OS.

Resolves: #101871
Related: #98434
Related: #98447
Releases: main, 12.4, 11.5
Change-Id: Ifafadceae3742da23fd1a40e5aab50074e60313c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80904
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>

typo3/sysext/core/Classes/Composer/PackageArtifactBuilder.php

@@ -275,11 +275,31 @@ private function publishResources(array $installedTypo3Packages): void
             [$relativePrefix] = explode('Resources/Public', $relativePath);
             $publicResourcesPath = $this->fileSystem->normalizePath($this->config->get('web-dir') . '/_assets/' . md5($relativePrefix));
             $this->fileSystem->ensureDirectoryExists(dirname($publicResourcesPath));
-            if (Platform::isWindows() && !$this->fileSystem->isJunction($publicResourcesPath)) {
-                $this->fileSystem->junction($fileSystemResourcesPath, $publicResourcesPath);
-            } elseif (!$this->fileSystem->isSymlinkedDirectory($publicResourcesPath)) {
-                $this->fileSystem->relativeSymlink($fileSystemResourcesPath, $publicResourcesPath);
+            if (Platform::isWindows()) {
+                $this->ensureJunctionExists($fileSystemResourcesPath, $publicResourcesPath);
+            } else {
+                $this->ensureSymlinkExists($fileSystemResourcesPath, $publicResourcesPath);
             }
         }
     }
+
+    private function ensureJunctionExists(string $target, string $junction): void
+    {
+        if (!$this->fileSystem->isJunction($junction)) {
+            // Cleanup a possible symlink that might have been installed by ourselves prior to #98434
+            // Note: Unprivileged deletion of symlinks is allowed, even if they were created by a
+            // privileged user
+            if (is_link($junction)) {
+                $this->fileSystem->unlink($junction);
+            }
+            $this->fileSystem->junction($target, $junction);
+        }
+    }
+
+    private function ensureSymlinkExists(string $target, string $link): void
+    {
+        if (!$this->fileSystem->isSymlinkedDirectory($link)) {
+            $this->fileSystem->relativeSymlink($target, $link);
+        }
+    }
 }