Fix unhandled promise rejection (#105)

Author: ehmicky

source/iterable.js

@@ -16,12 +16,25 @@ export const lineIterator = async function * (subprocess, {state}, streamName) {
 			return;
 		}
 
+		handleErrors(subprocess);
 		yield * readline.createInterface({input: stream});
 	} finally {
 		await subprocess;
 	}
 };
 
+// When the `subprocess` promise is rejected, we await it in the `finally`
+// block. However, this might not happen right away, so an `unhandledRejection`
+// error is emitted first, crashing the process. This prevents it.
+// This is safe since we are guaranteed to propagate the `subprocess` error
+// with the `finally` block.
+// See https://github.com/sindresorhus/nano-spawn/issues/104
+const handleErrors = async subprocess => {
+	try {
+		await subprocess;
+	} catch {}
+};
+
 // Merge two async iterators into one
 export const combineAsyncIterators = async function * (...iterators) {
 	try {

test/iterable.js

@@ -8,7 +8,7 @@ import {
 	fourthTestString,
 	multibyteString,
 } from './helpers/arguments.js';
-import {assertFail, assertErrorEvent} from './helpers/assert.js';
+import {assertAbortError, assertFail, assertErrorEvent} from './helpers/assert.js';
 import {
 	nodeEval,
 	nodePrintStdout,
@@ -19,6 +19,7 @@ import {
 	nodePassThrough,
 	nodePassThroughPrint,
 	nodePassThroughPrintFail,
+	nodeHanging,
 } from './helpers/commands.js';
 
 const getIterable = (subprocess, iterableType) => iterableType === ''
@@ -222,6 +223,21 @@ const testStreamIterateAllError = async (t, streamName) => {
 test('Handles subprocess.stdout error in subprocess[Symbol.asyncIterator]', testStreamIterateAllError, 'stdout');
 test('Handles subprocess.stderr error in subprocess[Symbol.asyncIterator]', testStreamIterateAllError, 'stderr');
 
+const testStreamIterateSignal = async (t, streamName) => {
+	const signal = AbortSignal.timeout(0);
+	const subprocess = spawn(...nodeHanging, {signal});
+	const error = await t.throwsAsync(arrayFromAsync(subprocess[streamName]));
+	assertAbortError(t, error, signal.reason);
+	const promiseError = await t.throwsAsync(subprocess);
+	t.is(promiseError, error);
+	t.is(promiseError.stdout, '');
+	t.is(promiseError.stderr, '');
+	t.is(promiseError.output, '');
+};
+
+test('Handles subprocess.stdout error with the "signal" option', testStreamIterateSignal, 'stdout');
+test('Handles subprocess.stderr error with the "signal" option', testStreamIterateSignal, 'stderr');
+
 // eslint-disable-next-line max-params
 const iterateOnOutput = async (t, subprocess, state, cause, shouldThrow, iterableType) => {
 	// eslint-disable-next-line no-unreachable-loop