fix(core): settle the prompt when its input ends

.changeset/lucky-pandas-listen.md

@@ -0,0 +1,5 @@
+---
+"@clack/core": patch
+---
+
+Settle a prompt as cancelled when its input ends, instead of leaving the promise pending with the cursor hidden.

packages/core/src/prompts/prompt.ts

@@ -177,6 +177,11 @@ export default class Prompt<TValue> {
 			}
 
 			this.input.on('keypress', this.onKeypress);
+			// An input stream that ends (closed stdin, a pipe that ran out, an agent
+			// shell) leaves nothing to read, so the prompt has to settle the way Ctrl-C
+			// does rather than keep the promise pending with the cursor hidden.
+			this.input.on('end', this.onInputEnd);
+			this.input.on('close', this.onInputEnd);
 			setRawMode(this.input, true);
 			this.output.on('resize', this.render);
 
@@ -194,6 +199,11 @@ export default class Prompt<TValue> {
 				setRawMode(this.input, false);
 				resolve(CANCEL_SYMBOL);
 			});
+
+			// An input that ended before the prompt started has no event left to fire.
+			if (this.input.readableEnded || this.input.destroyed) {
+				this.onInputEnd();
+			}
 		});
 	}
 
@@ -224,6 +234,16 @@ export default class Prompt<TValue> {
 		this._setUserInput('');
 	}
 
+	private onInputEnd = (): void => {
+		// `close()` clears the interface; a second end event (the stream is shared
+		// between prompts) must not reopen a settled prompt.
+		if (this.rl === undefined) {
+			return;
+		}
+		this.state = 'cancel';
+		this.close();
+	};
+
 	private async onKeypress(char: string | undefined, key: Key) {
 		if (this.state === 'validating') {
 			return;
@@ -263,6 +283,12 @@ export default class Prompt<TValue> {
 					this.state = 'validating';
 					this.render();
 					problem = await problemResult;
+					// The prompt can close while an async validator runs (the abort
+					// signal, or the input ending): a closed prompt must not then emit
+					// a submit for a value nobody read.
+					if (this.rl === undefined) {
+						return;
+					}
 				} else {
 					problem = problemResult;
 				}
@@ -293,6 +319,8 @@ export default class Prompt<TValue> {
 	protected close() {
 		this.input.unpipe();
 		this.input.removeListener('keypress', this.onKeypress);
+		this.input.removeListener('end', this.onInputEnd);
+		this.input.removeListener('close', this.onInputEnd);
 		this.output.write('\n');
 		setRawMode(this.input, false);
 		this.rl?.close();

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

@@ -1,4 +1,5 @@
 import { type } from 'arktype';
+import { Readable } from 'node:stream';
 import { cursor } from 'sisteransi';
 import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
 import { default as Prompt } from '../../src/prompts/prompt.js';
@@ -475,3 +476,49 @@ describe('Prompt', () => {
 		expect(instance.error).to.equal('');
 	});
 });
+
+describe('Prompt with an input that ends', () => {
+	let input: MockReadable;
+	let output: MockWritable;
+
+	beforeEach(() => {
+		input = new MockReadable();
+		output = new MockWritable();
+	});
+
+	test('cancels when the input ends while it is waiting', async () => {
+		const instance = new Prompt({ input, output, render: () => 'foo' });
+		const resultPromise = instance.prompt();
+		input.emit('end');
+		const result = await resultPromise;
+		expect(isCancel(result)).to.equal(true);
+		expect(instance.state).to.equal('cancel');
+		expect(output.buffer).to.deep.equal([cursor.hide, 'foo', '\n', cursor.show]);
+	});
+
+	test('cancels when the input already ended before it starts', async () => {
+		// A stream that has finished emits `end` once; a prompt attached afterwards
+		// never sees it, which is the "stdin ended before the prompt started" case.
+		const ended = new Readable({ read() {} });
+		const endEvent = new Promise<void>((resolve) => ended.once('end', () => resolve()));
+		ended.push(null);
+		ended.resume();
+		await endEvent;
+		expect(ended.readableEnded).to.equal(true);
+
+		const instance = new Prompt({ input: ended, output, render: () => 'foo' });
+		const result = await instance.prompt();
+		expect(isCancel(result)).to.equal(true);
+		expect(instance.state).to.equal('cancel');
+	});
+
+	test('keeps the submitted value when the input ends after settling', async () => {
+		const instance = new Prompt({ input, output, render: () => 'foo' });
+		const resultPromise = instance.prompt();
+		input.emit('keypress', '', { name: 'return' });
+		const result = await resultPromise;
+		expect(isCancel(result)).to.equal(false);
+		input.emit('end');
+		expect(instance.state).to.equal('submit');
+	});
+});