fix(core): cancel prompts when the input stream ends

.changeset/quiet-pipes-end.md

@@ -0,0 +1,5 @@
+---
+"@clack/core": patch
+---
+
+Cancel a prompt when its input stream ends (e.g. stdin is `/dev/null` or piped input runs out) instead of leaving the returned promise pending forever.

packages/core/src/prompts/prompt.ts

@@ -70,6 +70,7 @@ export default class Prompt<TValue> {
 
 		this.opts = opts;
 		this.onKeypress = this.onKeypress.bind(this);
+		this.onInputEnd = this.onInputEnd.bind(this);
 		this.close = this.close.bind(this);
 		this.render = this.render.bind(this);
 		this._render = render.bind(this);
@@ -194,9 +195,27 @@ export default class Prompt<TValue> {
 				setRawMode(this.input, false);
 				resolve(CANCEL_SYMBOL);
 			});
+
+			// No answer can arrive once the input has ended (e.g. stdin is
+			// `/dev/null` or a pipe that ran out), so cancel instead of hanging.
+			if (this.input.readableEnded) {
+				this.onInputEnd();
+			} else {
+				this.input.once('end', this.onInputEnd);
+			}
 		});
 	}
 
+	private onInputEnd() {
+		if (this.state === 'submit' || this.state === 'cancel') {
+			return;
+		}
+		this.state = 'cancel';
+		this.emit('finalize');
+		this.render();
+		this.close();
+	}
+
 	protected _isActionKey(char: string | undefined, _key: Key): boolean {
 		return char === '\t';
 	}
@@ -293,6 +312,7 @@ export default class Prompt<TValue> {
 	protected close() {
 		this.input.unpipe();
 		this.input.removeListener('keypress', this.onKeypress);
+		this.input.removeListener('end', this.onInputEnd);
 		this.output.write('\n');
 		setRawMode(this.input, false);
 		this.rl?.close();

packages/core/test/prompts/prompt.test.ts

@@ -236,6 +236,54 @@ describe('Prompt', () => {
 		expect(instance.state).to.equal('cancel');
 	});
 
+	test('cancels when the input ends', async () => {
+		const instance = new Prompt({
+			input,
+			output,
+			render: () => 'foo',
+		});
+		const resultPromise = instance.prompt();
+		input.close();
+		input.resume();
+
+		const result = await resultPromise;
+		expect(isCancel(result)).to.equal(true);
+		expect(instance.state).to.equal('cancel');
+		expect(output.buffer.at(-1)).to.equal(cursor.show);
+		expect(input.listenerCount('end')).to.equal(0);
+	});
+
+	test('cancels immediately if the input has already ended', async () => {
+		input.close();
+		input.resume();
+		await new Promise((resolve) => input.once('end', resolve));
+
+		const instance = new Prompt({
+			input,
+			output,
+			render: () => 'foo',
+		});
+		const result = await instance.prompt();
+		expect(isCancel(result)).to.equal(true);
+		expect(instance.state).to.equal('cancel');
+	});
+
+	test('does not cancel a submitted prompt when the input ends afterwards', async () => {
+		const instance = new Prompt({
+			input,
+			output,
+			render: () => 'foo',
+		});
+		const resultPromise = instance.prompt();
+		input.emit('keypress', '', { name: 'return' });
+		input.close();
+		input.resume();
+
+		const result = await resultPromise;
+		expect(isCancel(result)).to.equal(false);
+		expect(instance.state).to.equal('submit');
+	});
+
 	describe('function validation', () => {
 		test('accepts invalid initial value', () => {
 			const instance = new Prompt({