Better error message on IPC EPIPE (#1088)

lib/ipc/send.js

@@ -1,5 +1,6 @@
 import {
 	validateIpcMethod,
+	handleEpipeError,
 	handleSerializationError,
 	disconnect,
 } from './validation.js';
@@ -33,6 +34,7 @@ const sendMessageAsync = async ({anyProcess, anyProcessSend, isSubprocess, messa
 		await anyProcessSend(message);
 	} catch (error) {
 		disconnect(anyProcess);
+		handleEpipeError(error, isSubprocess);
 		handleSerializationError(error, isSubprocess, message);
 		throw error;
 	} finally {

lib/ipc/validation.js

@@ -28,6 +28,13 @@ const getNamespaceName = isSubprocess => isSubprocess ? '' : 'subprocess.';
 
 const getOtherProcessName = isSubprocess => isSubprocess ? 'parent process' : 'subprocess';
 
+// EPIPE can happen when sending a message to a subprocess that is closing but has not disconnected yet
+export const handleEpipeError = (error, isSubprocess) => {
+	if (error.code === 'EPIPE') {
+		throw new Error(`${getNamespaceName(isSubprocess)}sendMessage() cannot be used: the ${getOtherProcessName(isSubprocess)} is disconnecting.`, {cause: error});
+	}
+};
+
 // Better error message when sending messages which cannot be serialized.
 // Works with both `serialization: 'advanced'` and `serialization: 'json'`.
 export const handleSerializationError = (error, isSubprocess, message) => {

test/ipc/send.js

@@ -81,3 +81,29 @@ test('Disconnects IPC on subprocess.sendMessage() error', async t => {
 	t.false(isTerminated);
 	t.true(stderr.includes('sendMessage()\'s argument type is invalid'));
 });
+
+// EPIPE happens based on timing conditions, so we must repeat it until it happens
+const findEpipeError = async t => {
+	// eslint-disable-next-line no-constant-condition
+	while (true) {
+		// eslint-disable-next-line no-await-in-loop
+		const error = await t.throwsAsync(getEpipeError());
+		if (error.cause?.code === 'EPIPE') {
+			return error;
+		}
+	}
+};
+
+const getEpipeError = async () => {
+	const subprocess = execa('empty.js', {ipc: true});
+	// eslint-disable-next-line no-constant-condition
+	while (true) {
+		// eslint-disable-next-line no-await-in-loop
+		await subprocess.sendMessage('.');
+	}
+};
+
+test.serial('Can send messages while the subprocess is closing', async t => {
+	const {message} = await findEpipeError(t);
+	t.is(message, 'subprocess.sendMessage() cannot be used: the subprocess is disconnecting.');
+});