Exec: throw error when cwd option does not exist (#793)

* Exec: throw error when cwd option does not exist

* Simplify promise rejection

packages/exec/__tests__/exec.test.ts

@@ -538,6 +538,22 @@ describe('@actions/exec', () => {
     expect(output.trim()).toBe(`args[0]: "hello"${os.EOL}args[1]: "world"`)
   })
 
+  it('Exec roots throws friendly error when bad cwd is specified', async () => {
+    const execOptions = getExecOptions()
+    execOptions.cwd = 'nonexistent/path'
+
+    await expect(exec.exec('ls', ['-all'], execOptions)).rejects.toThrowError(
+      `The cwd: ${execOptions.cwd} does not exist!`
+    )
+  })
+
+  it('Exec roots does not throw when valid cwd is provided', async () => {
+    const execOptions = getExecOptions()
+    execOptions.cwd = './'
+
+    await expect(exec.exec('ls', ['-all'], execOptions)).resolves.toBe(0)
+  })
+
   it('Exec roots relative tool path using rooted options.cwd', async () => {
     let command: string
     if (IS_WINDOWS) {

packages/exec/src/toolrunner.ts

@@ -414,7 +414,7 @@ export class ToolRunner extends events.EventEmitter {
     // otherwise verify it exists (add extension on Windows if necessary)
     this.toolPath = await io.which(this.toolPath, true)
 
-    return new Promise<number>((resolve, reject) => {
+    return new Promise<number>(async (resolve, reject) => {
       this._debug(`exec tool: ${this.toolPath}`)
       this._debug('arguments:')
       for (const arg of this.args) {
@@ -433,6 +433,10 @@ export class ToolRunner extends events.EventEmitter {
         this._debug(message)
       })
 
+      if (this.options.cwd && !(await ioUtil.exists(this.options.cwd))) {
+        return reject(new Error(`The cwd: ${this.options.cwd} does not exist!`))
+      }
+
       const fileName = this._getSpawnFileName()
       const cp = child.spawn(
         fileName,