TODO: Check functionality and fix tests

Update: README, action file

README.md

@@ -52,10 +52,25 @@ steps:
   - uses: actions/checkout@master
   - uses: actions/setup-go@v2
     with:
-      go-version: '1.9.3' # The Go version to download (if necessary) and use.
+      go-version: '1.16.1' # The Go version to download (if necessary) and use.
   - run: go run hello.go
 ```
 
+
+Check latest version:  
+> In basic example, without `check-latest` flag, the action tries to resolve version from local cache firstly and download only if it is not found. Local cache on image is updated with a couple of weeks latency.  
+`check-latest` flag forces the action to check if the cached version is the latest one. It reduces latency significantly but it is much more likely to incur version downloading.
+```yaml
+steps:
+  - uses: actions/checkout@master
+  - uses: actions/setup-go@v2
+    with:
+      go-version: '1.14'
+      check-latest: true
+  - run: go run hello.go
+```
+
+
 Matrix Testing:
 ```yaml
 jobs:

__tests__/setup-go.test.ts

@@ -573,4 +573,158 @@ describe('setup-go', () => {
   it('does not convert exact versions', async () => {
     expect(im.makeSemver('1.13.1')).toBe('1.13.1');
   });
+
+  describe('check-latest flag', () => {
+    it("use local version and don't check manifest if check-latest is not specified", async () => {
+      os.platform = 'linux';
+      os.arch = 'x64';
+
+      inputs['go-version'] = '1.16';
+      inputs['check-latest'] = 'false';
+
+      const toolPath = path.normalize('/cache/go/1.16.1/x64');
+      findSpy.mockReturnValue(toolPath);
+      await main.run();
+
+      expect(logSpy).toHaveBeenCalledWith(`Found in cache @ ${toolPath}`);
+      expect(logSpy).not.toHaveBeenCalledWith(
+        'Attempt to resolve the latest version from manifest...'
+      );
+    });
+
+    it('check latest version and resolve it from local cache', async () => {
+      os.platform = 'linux';
+      os.arch = 'x64';
+
+      inputs['go-version'] = '1.16.1';
+      inputs['check-latest'] = 'true';
+
+      const toolPath = path.normalize('/cache/go/1.16.1/x64');
+      findSpy.mockReturnValue(toolPath);
+      dlSpy.mockImplementation(async () => '/some/temp/path');
+      exSpy.mockImplementation(async () => '/some/other/temp/path');
+      cacheSpy.mockImplementation(async () => toolPath);
+
+      await main.run();
+
+      expect(logSpy).toHaveBeenCalledWith(
+        'Attempt to resolve the latest version from manifest...'
+      );
+      expect(logSpy).toHaveBeenCalledWith("Resolved as '1.16.1'");
+      expect(logSpy).toHaveBeenCalledWith(`Found in cache @ ${toolPath}`);
+    });
+
+    it('check latest version and install it from manifest', async () => {
+      os.platform = 'linux';
+      os.arch = 'x64';
+
+      inputs['go-version'] = '1.16.13';
+      inputs['check-latest'] = 'true';
+
+      findSpy.mockImplementation(() => '');
+      dlSpy.mockImplementation(async () => '/some/temp/path');
+      const toolPath = path.normalize('/cache/go/1.16.13/x64');
+      exSpy.mockImplementation(async () => '/some/other/temp/path');
+      cacheSpy.mockImplementation(async () => toolPath);
+      const expectedUrl =
+        'https://github.com/actions/go-versions/releases/download/1.16.13-1668091716/go-1.16.13-linux-x64.tar.gz';
+
+      await main.run();
+
+      expect(logSpy).toHaveBeenCalledWith(
+        'Attempt to resolve the latest version from manifest...'
+      );
+      // expect(logSpy).toHaveBeenCalledWith("Resolved as '1.16.13'");
+      expect(logSpy).toHaveBeenCalledWith();
+      expect(logSpy).toHaveBeenCalledWith(
+        `Acquiring 1.16.13 from ${expectedUrl}`
+      );
+      expect(logSpy).toHaveBeenCalledWith('Extracting ...');
+    });
+
+    it('fallback to dist if version if not found in manifest', async () => {
+      os.platform = 'linux';
+      os.arch = 'x64';
+
+      // a version which is not in the manifest but is in node dist
+      let versionSpec = '1.16';
+
+      inputs['go-version'] = versionSpec;
+      inputs['check-latest'] = 'true';
+      inputs['always-auth'] = false;
+      inputs['token'] = 'faketoken';
+
+      // ... but not in the local cache
+      findSpy.mockImplementation(() => '');
+
+      dlSpy.mockImplementation(async () => '/some/temp/path');
+      // TODO: What should be here? 
+      let toolPath = path.normalize('/cache/go/1.15.15/x64');
+      exSpy.mockImplementation(async () => '/some/other/temp/path');
+      cacheSpy.mockImplementation(async () => toolPath);
+
+      await main.run();
+
+      let expPath = path.join(toolPath, 'bin');
+
+      expect(dlSpy).toHaveBeenCalled();
+      expect(exSpy).toHaveBeenCalled();
+      expect(logSpy).toHaveBeenCalledWith(
+        'Attempt to resolve the latest version from manifest...'
+      );
+      expect(logSpy).toHaveBeenCalledWith(
+        `Failed to resolve version ${versionSpec} from manifest`
+      );
+      expect(logSpy).toHaveBeenCalledWith(
+        `Attempting to download ${versionSpec}...`
+      );
+      // TODO: Is this exists. Should be something like `extPath = path.join(extPath, 'go');`
+      // expect(cnSpy).toHaveBeenCalledWith(`::add-path::${expPath}${osm.EOL}`);
+    });
+
+    it('fallback to dist if manifest is not available', async () => {
+      os.platform = 'linux';
+      os.arch = 'x64';
+
+      // a version which is not in the manifest but is in node dist
+      let versionSpec = '1.16';
+
+      inputs['go-version'] = versionSpec;
+      inputs['check-latest'] = 'true';
+      inputs['always-auth'] = false;
+      inputs['token'] = 'faketoken';
+
+      // ... but not in the local cache
+      findSpy.mockImplementation(() => '');
+      getManifestSpy.mockImplementation(() => {
+        throw new Error('Unable to download manifest');
+      });
+
+      dlSpy.mockImplementation(async () => '/some/temp/path');
+      let toolPath = path.normalize('/cache/go/1.16.1/x64');
+      exSpy.mockImplementation(async () => '/some/other/temp/path');
+      cacheSpy.mockImplementation(async () => toolPath);
+
+      await main.run();
+
+      let expPath = path.join(toolPath, 'bin');
+
+      expect(dlSpy).toHaveBeenCalled();
+      expect(exSpy).toHaveBeenCalled();
+      expect(logSpy).toHaveBeenCalledWith(
+        'Attempt to resolve the latest version from manifest...'
+      );
+      expect(logSpy).toHaveBeenCalledWith(
+        'Unable to resolve version from manifest...'
+      );
+      expect(logSpy).toHaveBeenCalledWith(
+        `Failed to resolve version ${versionSpec} from manifest`
+      );
+      expect(logSpy).toHaveBeenCalledWith(
+        `Attempting to download ${versionSpec}...`
+      );
+      // expect(cnSpy).toHaveBeenCalledWith(`::add-path::${expPath}${osm.EOL}`);
+    });
+  });
+
 });

action.yml

@@ -4,6 +4,9 @@ author: 'GitHub'
 inputs: 
   go-version:
     description: 'The Go version to download (if necessary) and use. Supports semver spec and ranges.'
+  check-latest:
+    description: 'Set this option if you want the action to check for the latest available version that satisfies the version spec'
+    default: false
   stable:
     description: 'Whether to download only stable versions'
     default: 'true'

src/installer.ts

@@ -31,10 +31,26 @@ export interface IGoVersionInfo {
 export async function getGo(
   versionSpec: string,
   stable: boolean,
+  checkLatest: boolean,
   auth: string | undefined
 ) {
   let osPlat: string = os.platform();
   let osArch: string = os.arch();
+  
+  if (checkLatest) {
+    core.info('Attempt to resolve the latest version from manifest...');
+    const resolvedVersion = await resolveVersionFromManifest(
+      versionSpec,
+      stable,
+      auth
+    );
+    if (resolvedVersion) {
+      versionSpec = resolvedVersion;
+      core.info(`Resolved as '${versionSpec}'`);
+    } else {
+      core.info(`Failed to resolve version ${versionSpec} from manifest`);
+    }
+  }
 
   // check cache
   let toolPath: string;
@@ -97,6 +113,20 @@ export async function getGo(
   return downloadPath;
 }
 
+async function resolveVersionFromManifest(
+  versionSpec: string,
+  stable: boolean,
+  auth: string | undefined
+): Promise<string | undefined> {
+  try {
+    const info = await getInfoFromManifest(versionSpec, stable, auth);
+    return info?.resolvedVersion;
+  } catch (err) {
+    core.info('Unable to resolve version from manifest...');
+    core.debug(err.message);
+  }
+}
+
 async function installGoVersion(
   info: IGoVersionInfo,
   auth: string | undefined

src/main.ts

@@ -24,7 +24,9 @@ export async function run() {
       let token = core.getInput('token');
       let auth = !token || isGhes() ? undefined : `token ${token}`;
 
-      const installDir = await installer.getGo(versionSpec, stable, auth);
+      const checkLatest =
+        (core.getInput('check-latest') || 'false').toUpperCase() === 'TRUE';
+      const installDir = await installer.getGo(versionSpec, stable, checkLatest, auth);
 
       core.exportVariable('GOROOT', installDir);
       core.addPath(path.join(installDir, 'bin'));