Improve toolchain handling

__tests__/setup-go.test.ts

@@ -285,7 +285,7 @@ describe('setup-go', () => {
     expect(logSpy).toHaveBeenCalledWith(`Setup go version spec 1.13.0`);
   });
 
-  it('does not export any variables for Go versions >=1.9', async () => {
+  it('does not export GOROOT for Go versions >=1.9', async () => {
     inputs['go-version'] = '1.13.0';
     inSpy.mockImplementation(name => inputs[name]);
 
@@ -298,7 +298,7 @@ describe('setup-go', () => {
     });
 
     await main.run();
-    expect(vars).toStrictEqual({});
+    expect(vars).not.toHaveProperty('GOROOT');
   });
 
   it('exports GOROOT for Go versions <1.9', async () => {
@@ -314,9 +314,7 @@ describe('setup-go', () => {
     });
 
     await main.run();
-    expect(vars).toStrictEqual({
-      GOROOT: toolPath
-    });
+    expect(vars).toHaveProperty('GOROOT', toolPath);
   });
 
   it('finds a version of go already in the cache', async () => {
@@ -989,4 +987,18 @@ use .
       }
     );
   });
+
+  it('exports GOTOOLCHAIN and sets it in current process env', async () => {
+    inputs['go-version'] = '1.21.0';
+    inSpy.mockImplementation(name => inputs[name]);
+
+    const vars: {[key: string]: string} = {};
+    exportVarSpy.mockImplementation((name: string, val: string) => {
+      vars[name] = val;
+    });
+
+    await main.run();
+    expect(vars).toStrictEqual({GOTOOLCHAIN: 'local'});
+    expect(process.env).toHaveProperty('GOTOOLCHAIN', 'local');
+  });
 });

dist/setup/index.js

@@ -93707,6 +93707,7 @@ const os_1 = __importDefault(__nccwpck_require__(2037));
 function run() {
     return __awaiter(this, void 0, void 0, function* () {
         try {
+            setToolchain();
             //
             // versionSpec is optional.  If supplied, install / use from the tool cache
             // If not supplied then problem matchers will still be setup.  Useful for self-hosted.
@@ -93820,6 +93821,21 @@ function resolveVersionInput() {
     }
     return version;
 }
+function setToolchain() {
+    // docs: https://go.dev/doc/toolchain
+    // "local indicates the bundled Go toolchain (the one that shipped with the go command being run)"
+    // this is so any 'go' command is run with the selected Go version
+    // and doesn't trigger a toolchain download and run commands with that
+    // see e.g. issue #424
+    // and a similar discussion: https://github.com/docker-library/golang/issues/472
+    const toolchain = 'local';
+    const toolchainVar = 'GOTOOLCHAIN';
+    // set the value in process env so any `go` commands run as child-process
+    // don't cause toolchain downloads
+    process.env[toolchainVar] = toolchain;
+    // and in the runner env so e.g. a user running `go mod tidy` won't cause it
+    core.exportVariable(toolchainVar, toolchain);
+}
 
 
 /***/ }),

src/main.ts

@@ -11,6 +11,7 @@ import os from 'os';
 
 export async function run() {
   try {
+    setToolchain();
     //
     // versionSpec is optional.  If supplied, install / use from the tool cache
     // If not supplied then problem matchers will still be setup.  Useful for self-hosted.
@@ -160,3 +161,20 @@ function resolveVersionInput(): string {
 
   return version;
 }
+
+function setToolchain() {
+  // docs: https://go.dev/doc/toolchain
+  // "local indicates the bundled Go toolchain (the one that shipped with the go command being run)"
+  // this is so any 'go' command is run with the selected Go version
+  // and doesn't trigger a toolchain download and run commands with that
+  // see e.g. issue #424
+  // and a similar discussion: https://github.com/docker-library/golang/issues/472
+  const toolchain = 'local';
+  const toolchainVar = 'GOTOOLCHAIN';
+
+  // set the value in process env so any `go` commands run as child-process
+  // don't cause toolchain downloads
+  process.env[toolchainVar] = toolchain;
+  // and in the runner env so e.g. a user running `go mod tidy` won't cause it
+  core.exportVariable(toolchainVar, toolchain);
+}