feat: add go-download-base-url input for custom Go distributions (#721)

* feat: add go-download-base-url input for custom Go distributions

Add support for downloading Go from custom sources such as Microsoft Go
(aka.ms). Users can specify a custom download base URL via the
`go-download-base-url` input or the `GO_DOWNLOAD_BASE_URL` environment
variable (input takes precedence).

When a custom URL is provided, the action skips the GitHub-hosted
manifest and attempts to resolve versions from the custom URL's JSON
listing. If the listing is unavailable (as with aka.ms redirect links),
it falls back to constructing the download URL directly from the
version, platform, and architecture.

Usage:
  - uses: actions/setup-go@v6
    with:
      go-version: '1.25'
      go-download-base-url: 'https://aka.ms/golang/release/latest'

Changes:
- action.yml: add go-download-base-url optional input
- installer.ts: add getInfoFromDirectDownload() for URL construction
  fallback, thread custom URL through getGo/getInfoFromDist/findMatch
- main.ts: read new input and GO_DOWNLOAD_BASE_URL env var
- setup-go.test.ts: add 12 unit tests for custom URL behavior
- microsoft-validation.yml: add E2E workflow testing Microsoft build of Go
  across ubuntu/windows/macos with versions 1.24 and 1.25
- README.md: document new input with Microsoft build of Go examples

* run prettier

* fixup PR review

* revert cache-save

* fixup

* handle distinct cache

* skip json for known URL

* fix bug in JSON with custom URL

dist/setup/index.js

@@ -77034,9 +77034,11 @@ var __importDefault = (this && this.__importDefault) || function (mod) {
 Object.defineProperty(exports, "__esModule", ({ value: true }));
 exports.GOTOOLCHAIN_LOCAL_VAL = exports.GOTOOLCHAIN_ENV_VAR = void 0;
 exports.getGo = getGo;
+exports.customToolCacheName = customToolCacheName;
 exports.extractGoArchive = extractGoArchive;
 exports.getManifest = getManifest;
 exports.getInfoFromManifest = getInfoFromManifest;
+exports.getInfoFromDirectDownload = getInfoFromDirectDownload;
 exports.findMatch = findMatch;
 exports.getVersionsDist = getVersionsDist;
 exports.makeSemver = makeSemver;
@@ -77048,6 +77050,8 @@ const path = __importStar(__nccwpck_require__(16928));
 const semver = __importStar(__nccwpck_require__(62088));
 const httpm = __importStar(__nccwpck_require__(54844));
 const sys = __importStar(__nccwpck_require__(57666));
+const crypto_1 = __importDefault(__nccwpck_require__(76982));
+const child_process_1 = __importDefault(__nccwpck_require__(35317));
 const fs_1 = __importDefault(__nccwpck_require__(79896));
 const os_1 = __importDefault(__nccwpck_require__(70857));
 const utils_1 = __nccwpck_require__(71798);
@@ -77057,14 +77061,23 @@ const MANIFEST_REPO_OWNER = 'actions';
 const MANIFEST_REPO_NAME = 'go-versions';
 const MANIFEST_REPO_BRANCH = 'main';
 const MANIFEST_URL = `https://raw.githubusercontent.com/${MANIFEST_REPO_OWNER}/${MANIFEST_REPO_NAME}/${MANIFEST_REPO_BRANCH}/versions-manifest.json`;
+const DEFAULT_GO_DOWNLOAD_BASE_URL = 'https://go.dev/dl';
 const GOLANG_DOWNLOAD_URL = 'https://go.dev/dl/?mode=json&include=all';
+// Base URLs known to not serve a version listing JSON endpoint.
+// For these URLs we skip the getInfoFromDist() call entirely and construct
+// the download URL directly, avoiding a guaranteed-404 HTTP request.
+const NO_VERSION_LISTING_BASE_URLS = ['https://aka.ms/golang/release/latest'];
 function getGo(versionSpec_1, checkLatest_1, auth_1) {
-    return __awaiter(this, arguments, void 0, function* (versionSpec, checkLatest, auth, arch = os_1.default.arch()) {
+    return __awaiter(this, arguments, void 0, function* (versionSpec, checkLatest, auth, arch = os_1.default.arch(), goDownloadBaseUrl) {
         var _a;
         let manifest;
         const osPlat = os_1.default.platform();
+        const customBaseUrl = goDownloadBaseUrl === null || goDownloadBaseUrl === void 0 ? void 0 : goDownloadBaseUrl.replace(/\/+$/, '');
         if (versionSpec === utils_1.StableReleaseAlias.Stable ||
             versionSpec === utils_1.StableReleaseAlias.OldStable) {
+            if (customBaseUrl) {
+                throw new Error(`Version aliases '${versionSpec}' are not supported with a custom download base URL. Please specify an exact Go version.`);
+            }
             manifest = yield getManifest(auth);
             let stableVersion = yield resolveStableVersionInput(versionSpec, arch, osPlat, manifest);
             if (!stableVersion) {
@@ -77077,18 +77090,28 @@ function getGo(versionSpec_1, checkLatest_1, auth_1) {
             versionSpec = stableVersion;
         }
         if (checkLatest) {
-            core.info('Attempting to resolve the latest version from the manifest...');
-            const resolvedVersion = yield resolveVersionFromManifest(versionSpec, true, auth, arch, manifest);
-            if (resolvedVersion) {
-                versionSpec = resolvedVersion;
-                core.info(`Resolved as '${versionSpec}'`);
+            if (customBaseUrl) {
+                core.info('check-latest is not supported with a custom download base URL. Using the provided version spec directly.');
             }
             else {
-                core.info(`Failed to resolve version ${versionSpec} from manifest`);
+                core.info('Attempting to resolve the latest version from the manifest...');
+                const resolvedVersion = yield resolveVersionFromManifest(versionSpec, true, auth, arch, manifest);
+                if (resolvedVersion) {
+                    versionSpec = resolvedVersion;
+                    core.info(`Resolved as '${versionSpec}'`);
+                }
+                else {
+                    core.info(`Failed to resolve version ${versionSpec} from manifest`);
+                }
             }
         }
+        // Use a distinct tool cache name for custom downloads to avoid
+        // colliding with the runner's pre-installed Go
+        const toolCacheName = customBaseUrl
+            ? customToolCacheName(customBaseUrl)
+            : 'go';
         // check cache
-        const toolPath = tc.find('go', versionSpec, arch);
+        const toolPath = tc.find(toolCacheName, versionSpec, arch);
         // If not found in cache, download
         if (toolPath) {
             core.info(`Found in cache @ ${toolPath}`);
@@ -77097,43 +77120,79 @@ function getGo(versionSpec_1, checkLatest_1, auth_1) {
         core.info(`Attempting to download ${versionSpec}...`);
         let downloadPath = '';
         let info = null;
-        //
-        // Try download from internal distribution (popular versions only)
-        //
-        try {
-            info = yield getInfoFromManifest(versionSpec, true, auth, arch, manifest);
-            if (info) {
-                downloadPath = yield installGoVersion(info, auth, arch);
+        if (customBaseUrl) {
+            //
+            // Download from custom base URL
+            //
+            const skipVersionListing = NO_VERSION_LISTING_BASE_URLS.some(url => customBaseUrl.toLowerCase() === url.toLowerCase());
+            if (skipVersionListing) {
+                core.info('Skipping version listing for known direct-download URL. Constructing download URL directly.');
+                info = getInfoFromDirectDownload(versionSpec, arch, customBaseUrl);
             }
             else {
-                core.info('Not found in manifest.  Falling back to download directly from Go');
-            }
-        }
-        catch (err) {
-            if (err instanceof tc.HTTPError &&
-                (err.httpStatusCode === 403 || err.httpStatusCode === 429)) {
-                core.info(`Received HTTP status code ${err.httpStatusCode}.  This usually indicates the rate limit has been exceeded`);
-            }
-            else {
-                core.info(err.message);
-            }
-            core.debug((_a = err.stack) !== null && _a !== void 0 ? _a : '');
-            core.info('Falling back to download directly from Go');
-        }
-        //
-        // Download from storage.googleapis.com
-        //
-        if (!downloadPath) {
-            info = yield getInfoFromDist(versionSpec, arch);
-            if (!info) {
-                throw new Error(`Unable to find Go version '${versionSpec}' for platform ${osPlat} and architecture ${arch}.`);
+                try {
+                    info = yield getInfoFromDist(versionSpec, arch, customBaseUrl);
+                }
+                catch (_b) {
+                    core.info('Version listing not available from custom URL. Constructing download URL directly.');
+                }
+                if (!info) {
+                    info = getInfoFromDirectDownload(versionSpec, arch, customBaseUrl);
+                }
             }
             try {
-                core.info('Install from dist');
-                downloadPath = yield installGoVersion(info, undefined, arch);
+                core.info('Install from custom download URL');
+                downloadPath = yield installGoVersion(info, auth, arch, toolCacheName);
             }
             catch (err) {
-                throw new Error(`Failed to download version ${versionSpec}: ${err}`);
+                const downloadUrl = (info === null || info === void 0 ? void 0 : info.downloadUrl) || customBaseUrl;
+                if (err instanceof tc.HTTPError && err.httpStatusCode === 404) {
+                    throw new Error(`The requested Go version ${versionSpec} is not available for platform ${osPlat}/${arch}. ` +
+                        `Download URL returned HTTP 404: ${downloadUrl}`);
+                }
+                throw new Error(`Failed to download Go ${versionSpec} for platform ${osPlat}/${arch} ` +
+                    `from ${downloadUrl}: ${err}`);
+            }
+        }
+        else {
+            //
+            // Try download from internal distribution (popular versions only)
+            //
+            try {
+                info = yield getInfoFromManifest(versionSpec, true, auth, arch, manifest);
+                if (info) {
+                    downloadPath = yield installGoVersion(info, auth, arch);
+                }
+                else {
+                    core.info('Not found in manifest.  Falling back to download directly from Go');
+                }
+            }
+            catch (err) {
+                if (err instanceof tc.HTTPError &&
+                    (err.httpStatusCode === 403 || err.httpStatusCode === 429)) {
+                    core.info(`Received HTTP status code ${err.httpStatusCode}.  This usually indicates the rate limit has been exceeded`);
+                }
+                else {
+                    core.info(err.message);
+                }
+                core.debug((_a = err.stack) !== null && _a !== void 0 ? _a : '');
+                core.info('Falling back to download directly from Go');
+            }
+            //
+            // Download from storage.googleapis.com
+            //
+            if (!downloadPath) {
+                info = yield getInfoFromDist(versionSpec, arch);
+                if (!info) {
+                    throw new Error(`Unable to find Go version '${versionSpec}' for platform ${osPlat} and architecture ${arch}.`);
+                }
+                try {
+                    core.info('Install from dist');
+                    downloadPath = yield installGoVersion(info, undefined, arch);
+                }
+                catch (err) {
+                    throw new Error(`Failed to download version ${versionSpec}: ${err}`);
+                }
             }
         }
         return downloadPath;
@@ -77186,16 +77245,19 @@ function cacheWindowsDir(extPath, tool, version, arch) {
         return defaultToolCacheDir;
     });
 }
-function addExecutablesToToolCache(extPath, info, arch) {
-    return __awaiter(this, void 0, void 0, function* () {
-        const tool = 'go';
+function addExecutablesToToolCache(extPath_1, info_1, arch_1) {
+    return __awaiter(this, arguments, void 0, function* (extPath, info, arch, toolName = 'go') {
         const version = makeSemver(info.resolvedVersion);
-        return ((yield cacheWindowsDir(extPath, tool, version, arch)) ||
-            (yield tc.cacheDir(extPath, tool, version, arch)));
+        return ((yield cacheWindowsDir(extPath, toolName, version, arch)) ||
+            (yield tc.cacheDir(extPath, toolName, version, arch)));
     });
 }
-function installGoVersion(info, auth, arch) {
-    return __awaiter(this, void 0, void 0, function* () {
+function customToolCacheName(baseUrl) {
+    const hash = crypto_1.default.createHash('sha256').update(baseUrl).digest('hex');
+    return `go-${hash.substring(0, 8)}`;
+}
+function installGoVersion(info_1, auth_1, arch_1) {
+    return __awaiter(this, arguments, void 0, function* (info, auth, arch, toolName = 'go') {
         core.info(`Acquiring ${info.resolvedVersion} from ${info.downloadUrl}`);
         // Windows requires that we keep the extension (.zip) for extraction
         const isWindows = os_1.default.platform() === 'win32';
@@ -77208,12 +77270,33 @@ function installGoVersion(info, auth, arch) {
         if (info.type === 'dist') {
             extPath = path.join(extPath, 'go');
         }
+        // For custom downloads, detect the actual installed version so the cache
+        // key reflects the real patch level (e.g. input "1.20" may install 1.20.14).
+        if (toolName !== 'go') {
+            const actualVersion = detectInstalledGoVersion(extPath);
+            if (actualVersion && actualVersion !== info.resolvedVersion) {
+                core.info(`Requested version '${info.resolvedVersion}' resolved to installed version '${actualVersion}'`);
+                info.resolvedVersion = actualVersion;
+            }
+        }
         core.info('Adding to the cache ...');
-        const toolCacheDir = yield addExecutablesToToolCache(extPath, info, arch);
+        const toolCacheDir = yield addExecutablesToToolCache(extPath, info, arch, toolName);
         core.info(`Successfully cached go to ${toolCacheDir}`);
         return toolCacheDir;
     });
 }
+function detectInstalledGoVersion(goDir) {
+    try {
+        const goBin = path.join(goDir, 'bin', os_1.default.platform() === 'win32' ? 'go.exe' : 'go');
+        const output = child_process_1.default.execFileSync(goBin, ['version'], { encoding: 'utf8' });
+        const match = output.match(/go version go(\S+)/);
+        return match ? match[1] : null;
+    }
+    catch (err) {
+        core.debug(`Failed to detect installed Go version: ${err.message}`);
+        return null;
+    }
+}
 function extractGoArchive(archivePath) {
     return __awaiter(this, void 0, void 0, function* () {
         const platform = os_1.default.platform();
@@ -77298,13 +77381,17 @@ function getInfoFromManifest(versionSpec_1, stable_1, auth_1) {
         return info;
     });
 }
-function getInfoFromDist(versionSpec, arch) {
+function getInfoFromDist(versionSpec, arch, goDownloadBaseUrl) {
     return __awaiter(this, void 0, void 0, function* () {
-        const version = yield findMatch(versionSpec, arch);
+        const dlUrl = goDownloadBaseUrl
+            ? `${goDownloadBaseUrl}/?mode=json&include=all`
+            : GOLANG_DOWNLOAD_URL;
+        const version = yield findMatch(versionSpec, arch, dlUrl);
         if (!version) {
             return null;
         }
-        const downloadUrl = `https://go.dev/dl/${version.files[0].filename}`;
+        const baseUrl = goDownloadBaseUrl || DEFAULT_GO_DOWNLOAD_BASE_URL;
+        const downloadUrl = `${baseUrl}/${version.files[0].filename}`;
         return {
             type: 'dist',
             downloadUrl: downloadUrl,
@@ -77313,13 +77400,36 @@ function getInfoFromDist(versionSpec, arch) {
         };
     });
 }
+function getInfoFromDirectDownload(versionSpec, arch, goDownloadBaseUrl) {
+    // Reject version specs that can't map to an artifact filename
+    if (/[~^>=<|*x]/.test(versionSpec)) {
+        throw new Error(`Version range '${versionSpec}' is not supported with a custom download base URL ` +
+            `when version listing is unavailable. Please specify an exact version (e.g., '1.25.0').`);
+    }
+    const archStr = sys.getArch(arch);
+    const platStr = sys.getPlatform();
+    const extension = platStr === 'windows' ? 'zip' : 'tar.gz';
+    // Ensure version has the 'go' prefix for the filename
+    const goVersion = versionSpec.startsWith('go')
+        ? versionSpec
+        : `go${versionSpec}`;
+    const fileName = `${goVersion}.${platStr}-${archStr}.${extension}`;
+    const downloadUrl = `${goDownloadBaseUrl}/${fileName}`;
+    core.info(`Constructed direct download URL: ${downloadUrl}`);
+    return {
+        type: 'dist',
+        downloadUrl: downloadUrl,
+        resolvedVersion: versionSpec.replace(/^go/, ''),
+        fileName: fileName
+    };
+}
 function findMatch(versionSpec_1) {
-    return __awaiter(this, arguments, void 0, function* (versionSpec, arch = os_1.default.arch()) {
+    return __awaiter(this, arguments, void 0, function* (versionSpec, arch = os_1.default.arch(), dlUrl = GOLANG_DOWNLOAD_URL) {
         const archFilter = sys.getArch(arch);
         const platFilter = sys.getPlatform();
         let result;
         let match;
-        const candidates = yield module.exports.getVersionsDist(GOLANG_DOWNLOAD_URL);
+        const candidates = yield module.exports.getVersionsDist(dlUrl);
         if (!candidates) {
             throw new Error(`golang download url did not return results`);
         }
@@ -77529,7 +77639,13 @@ function run() {
                 const token = core.getInput('token');
                 const auth = !token ? undefined : `token ${token}`;
                 const checkLatest = core.getBooleanInput('check-latest');
-                const installDir = yield installer.getGo(versionSpec, checkLatest, auth, arch);
+                const goDownloadBaseUrl = core.getInput('go-download-base-url') ||
+                    process.env['GO_DOWNLOAD_BASE_URL'] ||
+                    undefined;
+                if (goDownloadBaseUrl) {
+                    core.info(`Using custom Go download base URL: ${goDownloadBaseUrl}`);
+                }
+                const installDir = yield installer.getGo(versionSpec, checkLatest, auth, arch, goDownloadBaseUrl);
                 const installDirVersion = path_1.default.basename(path_1.default.dirname(installDir));
                 core.addPath(path_1.default.join(installDir, 'bin'));
                 core.info('Added go to the path');