Do not run symlink tests on Windows if symlinks are not supported (#26203)

* Do not run symlink tests on Windows if symlinks are not supported

Windows does not support symbolic links by default.  Tests fail for new
contributors on Windows if they do not adjust their Windows configuration
to allow symbolic links.

* Fast incremental build

* Create a symbolic link on Windows to confirm they are supported

* Fix the copyright year - 2026

GitHub Copilot caught the mistake

* Remove a white space change

* Revert "Fast incremental build"

Don't change production

This reverts commit 0750dd8.

* Fail tests on CI if Windows symlinks are not enabled

We do not want to fail the test on a developer computer if symlinks are
not enabled, but we do want to fail the test if a CI agent on Windows
does not have symbolic links enabled.

Author: MarkEWaite

test/src/test/java/hudson/model/DirectoryBrowserSupportTest.java

@@ -24,6 +24,7 @@
 
 package hudson.model;
 
+import static hudson.model.WindowsUtil.isWindowsSymlinkSupported;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.contains;
@@ -589,6 +590,8 @@ public boolean delete() {
     @Test
     @Issue("SECURITY-904")
     void symlink_outsideWorkspace_areNotAllowed() throws Exception {
+        assumeTrue(!Functions.isWindows() || isWindowsSymlinkSupported());
+
         FreeStyleProject p = j.createFreeStyleProject();
 
         File secretsFolder = new File(j.jenkins.getRootDir(), "secrets");
@@ -728,6 +731,8 @@ void symlink_outsideWorkspace_areNotAllowed() throws Exception {
     @Test
     @Issue("SECURITY-904")
     void symlink_avoidLeakingInformation_aboutIllegalFolder() throws Exception {
+        assumeTrue(!Functions.isWindows() || isWindowsSymlinkSupported());
+
         FreeStyleProject p = j.createFreeStyleProject();
 
         File secretsFolder = new File(j.jenkins.getRootDir(), "secrets");
@@ -800,7 +805,7 @@ void symlink_avoidLeakingInformation_aboutIllegalFolder() throws Exception {
     @Test
     @Issue("SECURITY-904")
     void junctionAndSymlink_outsideWorkspace_areNotAllowed_windowsJunction() throws Exception {
-        assumeTrue(Functions.isWindows());
+        assumeTrue(Functions.isWindows() && isWindowsSymlinkSupported());
 
         FreeStyleProject p = j.createFreeStyleProject();
 
@@ -1020,6 +1025,8 @@ void directSymlink_forTestingZip() throws Exception {
     @Test
     @Issue({"SECURITY-904", "SECURITY-1452"})
     void symlink_insideWorkspace_areNotAllowedAnymore() throws Exception {
+        assumeTrue(!Functions.isWindows() || isWindowsSymlinkSupported());
+
         FreeStyleProject p = j.createFreeStyleProject();
 
         // build once to have the workspace set up

test/src/test/java/hudson/model/WindowsUtil.java

@@ -0,0 +1,92 @@
+/*
+ * The MIT License
+ *
+ * Copyright (c) 2026
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package hudson.model;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * Utility methods for Windows specific details on tests.
+ *
+ * @author Mark Waite
+ */
+public class WindowsUtil {
+
+    private static final AtomicReference<Boolean> symlinkSupported = new AtomicReference<>();
+
+    /**
+     * Fail the test if running in CI and symlinks are not supported.
+     * We do not want to fail the test on a developer computer if
+     * symlinks are not enabled, but we do want to fail the test if a
+     * CI agent on Windows does not have symbolic links enabled.
+     */
+    private static void assertConfiguration(boolean supported) {
+        if (System.getenv("CI") != null) {
+            assertTrue(supported, "Jenkins CI configurations must enable symlinks on Windows");
+        }
+    }
+
+    /**
+     * Returns true if Windows allows a symbolic link to be created.
+     *
+     * @return true if Windows allows a symbolic link to be created.
+     * @throws IOException if creation or removal of temporary files fails
+     */
+    public static boolean isWindowsSymlinkSupported() throws IOException {
+        // Fast path, don't acquire unnecessary lock
+        Boolean supported = symlinkSupported.get();
+        if (supported != null) {
+            assertConfiguration(supported);
+            return supported;
+        }
+        synchronized (WindowsUtil.class) {
+            supported = symlinkSupported.get();
+            if (supported != null) {
+                assertConfiguration(supported);
+                return supported;
+            }
+            Path tempDir = Files.createTempDirectory("symlink-check");
+            Path target = Files.createFile(tempDir.resolve("target.txt"));
+            Path link = tempDir.resolve("link.txt");
+
+            try {
+                Files.createSymbolicLink(link, target);
+                Files.delete(link);
+                symlinkSupported.set(true);
+            } catch (IOException | UnsupportedOperationException uoe) {
+                symlinkSupported.set(false);
+            } finally {
+                Files.delete(target);
+                Files.delete(tempDir);
+            }
+        }
+        assertConfiguration(symlinkSupported.get());
+        return symlinkSupported.get();
+    }
+}

test/src/test/java/hudson/tasks/ArtifactArchiverTest.java

@@ -24,6 +24,7 @@
 
 package hudson.tasks;
 
+import static hudson.model.WindowsUtil.isWindowsSymlinkSupported;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.lessThan;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
@@ -281,6 +282,7 @@ void followSymlinksEnabledForOldConfig() throws Exception {
     @Issue("SECURITY-162")
     @Test
     void outsideSymlinks() throws Exception {
+        assumeTrue(!Functions.isWindows() || isWindowsSymlinkSupported());
         final FreeStyleProject p = j.createFreeStyleProject();
         p.getBuildersList().add(new TestBuilder() {
             @Override public boolean perform(AbstractBuild<?, ?> build, Launcher launcher, BuildListener listener) throws InterruptedException, IOException {
@@ -519,6 +521,7 @@ public boolean perform(AbstractBuild<?, ?> build, Launcher launcher, BuildListen
     @Test
     @Issue("JENKINS-55049")
     void lengthOfArtifactIsCorrect_eventForInvalidSymlink() throws Exception {
+        assumeTrue(!Functions.isWindows() || isWindowsSymlinkSupported());
         FreeStyleProject p = j.createFreeStyleProject();
         p.getBuildersList().add(new TestBuilder() {
             @Override public boolean perform(AbstractBuild<?, ?> build, Launcher launcher, BuildListener listener) throws InterruptedException, IOException {