Support absolute paths in node-version-file

__tests__/main.test.ts

@@ -177,6 +177,10 @@ describe('main tests', () => {
       );
     });
 
+    afterEach(() => {
+      jest.restoreAllMocks();
+    });
+
     each`
       contents                                                                                   | expected
       ${'12'}                                                                                    | ${'12'}
@@ -315,11 +319,39 @@ describe('main tests', () => {
 
       // Assert
       expect(getNodeVersionFromFileSpy).toHaveBeenCalled();
+      // A relative input is still resolved against the workspace.
+      expect(getNodeVersionFromFileSpy).toHaveBeenCalledWith(
+        path.join(process.env['GITHUB_WORKSPACE']!, '.nvmrc')
+      );
       expect(infoSpy).toHaveBeenCalledWith(
         `Resolved ${inputs['node-version-file']} as ${expectedVersionSpec}`
       );
     }, 10000);
 
+    it('reads node-version-file given as an absolute path outside the workspace', async () => {
+      // Arrange: a composite action passes `${{ github.action_path }}/.nvmrc`,
+      // which is absolute and may sit outside GITHUB_WORKSPACE.
+      // The workspace deliberately points at a different existing directory,
+      // so the absolute version file lies outside it.
+      const workspace = path.join(__dirname, 'mock');
+      process.env['GITHUB_WORKSPACE'] = workspace;
+      const versionFilePath = path.join(__dirname, 'data', '.nvmrc');
+      // Guard the premise: the version file lives outside the workspace.
+      expect(path.relative(workspace, versionFilePath).startsWith('..')).toBe(
+        true
+      );
+      inputs['node-version-file'] = versionFilePath;
+
+      // Act
+      await main.run();
+
+      // Assert: the path is used as provided and the real file is read.
+      // The expected `24` comes from `__tests__/data/.nvmrc` (`v24`).
+      expect(getNodeVersionFromFileSpy).toHaveBeenCalledWith(versionFilePath);
+      expect(infoSpy).toHaveBeenCalledWith(`Resolved ${versionFilePath} as 24`);
+      expect(core.setFailed as jest.Mock).not.toHaveBeenCalled();
+    }, 10000);
+
     it('should throw an error if node-version-file is not accessible', async () => {
       // Arrange
       inputs['node-version-file'] = 'non-existing-file';

dist/setup/index.js

@@ -101351,7 +101351,9 @@ function resolveVersionInput() {
         return version;
     }
     if (versionFileInput) {
-        const versionFilePath = external_path_.join(process.env.GITHUB_WORKSPACE, versionFileInput);
+        // `path.resolve` (unlike `path.join`) keeps an already-absolute input as-is,
+        // so a composite action can pass `${{ github.action_path }}/.nvmrc`.
+        const versionFilePath = external_path_.resolve(process.env.GITHUB_WORKSPACE, versionFileInput);
         const parsedVersion = getNodeVersionFromFile(versionFilePath);
         if (parsedVersion) {
             version = parsedVersion;

docs/advanced-usage.md

@@ -79,7 +79,7 @@ steps:
 The `node-version-file` input accepts a path to a file containing the version of Node.js to be used by a project, for example `.nvmrc`, `.node-version`, `.tool-versions`, `mise.toml`, or `package.json`. If both the `node-version` and the `node-version-file` inputs are provided then the `node-version` input is used.
 See [supported version syntax](https://github.com/actions/setup-node#supported-version-syntax).
 
-> The action will search for the node version file relative to the repository root.
+> The action resolves a relative `node-version-file` path against `GITHUB_WORKSPACE`, which is the repository root by default. If the input is a full absolute path, the action uses that path directly instead of appending it to the workspace.
 
 ```yaml
 steps:

src/main.ts

@@ -120,7 +120,9 @@ function resolveVersionInput(): string {
   }
 
   if (versionFileInput) {
-    const versionFilePath = path.join(
+    // `path.resolve` (unlike `path.join`) keeps an already-absolute input as-is,
+    // so a composite action can pass `${{ github.action_path }}/.nvmrc`.
+    const versionFilePath = path.resolve(
       process.env.GITHUB_WORKSPACE!,
       versionFileInput
     );