Produce error on prompt in non-tty environment. (#891)

* Produce error on prompt in non-tty environment.

* Fix build on node 8.

* Fix line order.

* Use Promise.reject()

README.md

@@ -62,6 +62,13 @@ inquirer
   ])
   .then(answers => {
     // Use user feedback for... whatever!!
+  })
+  .catch(error => {
+    if(error.isTtyError) {
+      // Prompt couldn't be rendered in the current environment
+    } else {
+      // Something else when wrong
+    }
   });
 ```
 
@@ -283,6 +290,10 @@ Launches an instance of the users preferred editor on a temporary file. Once the
 
 <a name="layouts"></a>
 
+### Use in Non-Interactive Environments
+`prompt()` requires that it is run in an interactive environment. (I.e. [One where `process.stdin.isTTY` is `true`](https://nodejs.org/docs/latest-v12.x/api/process.html#process_a_note_on_process_i_o)). If `prompt()` is invoked outside of such an environment, then `prompt()` will return a rejected promise with an error. For convenience, the error will have a `isTtyError` property to programmatically indicate the cause.
+
+
 ## User Interfaces and layouts
 
 Along with the prompts, Inquirer offers some basic text UI.

packages/inquirer/lib/inquirer.js

@@ -24,6 +24,16 @@ inquirer.ui = {
  */
 inquirer.createPromptModule = function(opt) {
   var promptModule = function(questions) {
+    // Check if prompt is being called in TTY environment
+    // If it isn't return a failed promise
+    if (!process.stdin.isTTY) {
+      const nonTtyError = new Error(
+        'Prompts can not be meaningfully rendered in non-TTY environments'
+      );
+      nonTtyError.isTtyError = true;
+      return Promise.reject(nonTtyError);
+    }
+
     var ui = new inquirer.ui.Prompt(promptModule.prompts, opt);
     var promise = ui.run(questions);
 

packages/inquirer/test/specs/inquirer.js

@@ -673,4 +673,32 @@ describe('inquirer.prompt', function() {
       expect(answers.q1).to.equal(true);
     });
   });
+
+  it('Throw an exception when run in non-tty', function() {
+    var original = process.stdin.isTTY;
+    delete process.stdin.isTTY;
+
+    var prompt = inquirer.createPromptModule();
+
+    var prompts = [
+      {
+        type: 'confirm',
+        name: 'q1',
+        message: 'message'
+      }
+    ];
+
+    var promise = prompt(prompts);
+
+    return promise
+      .then(() => {
+        // Failure
+        process.stdin.isTTY = original;
+        expect(true).to.equal(false);
+      })
+      .catch(error => {
+        process.stdin.isTTY = original;
+        expect(error.isTtyError).to.equal(true);
+      });
+  });
 });