uncaught exception from ProxyChannel.fromService

[mroch]

this code requires that IServerChannel.call returns a promise:

vscode/src/vs/base/parts/ipc/common/ipc.ts

Lines 420 to 428 in 9c17df5

	try {
	promise = channel.call(this.ctx, request.name, request.arg, cancellationTokenSource.token);
	} catch (err) {
	promise = Promise.reject(err);
	}
	const id = request.id;
	promise.then(data => {

otherwise, the then() call fails. in the example below, it returns undefined, which does not have a .then property.

but ProxyChannel.fromService is unsound. it is typed to return a Promise, but if target() doesn't return a promise then its return type is a lie:

vscode/src/vs/base/parts/ipc/common/ipc.ts

Lines 1108 to 1123 in 9c17df5

	call(_: unknown, command: string, args?: any[]): Promise<any> {
	const target = handler[command];
	if (typeof target === 'function') {
	// Revive unless marshalling disabled
	if (!disableMarshalling && Array.isArray(args)) {
	for (let i = 0; i < args.length; i++) {
	args[i] = revive(args[i]);
	}
	}
	return target.apply(handler, args);
	}
	throw new ErrorNoTelemetry(`Method not found: ${command}`);
	}

this ProxyChannel.fromService is a problem:

vscode/src/vs/code/node/sharedProcess/sharedProcessMain.ts

Lines 398 to 400 in 9c17df5

	// Custom Endpoint Telemetry
	const customEndpointTelemetryChannel = ProxyChannel.fromService(accessor.get(ICustomEndpointTelemetryService));
	this.server.registerChannel('customEndpointTelemetry', customEndpointTelemetryChannel);

because it has methods that don't return promises:

vscode/src/vs/platform/telemetry/common/telemetry.ts

Lines 65 to 66 in 9c17df5

	publicLog(endpoint: ITelemetryEndpoint, eventName: string, data?: ITelemetryData): void;
	publicLogError(endpoint: ITelemetryEndpoint, errorEventName: string, data?: ITelemetryData): void;

this leads to, in my case at least, an uncaught exception in sharedProcess.

I added this in ipc.ts and it logged this while debugging extensions:

if (!promise) {
  throw new Error(`Call returned undefined: ${request.channelName}.${request.name}(${request.arg})`);
}

Call returned undefined: customEndpointTelemetry.publicLog([object Object],js-debug/launch,[object Object])

[billti]

I've just spent quite a while debugging my own trivial extension and why it was failing to launch under the debugger to arrive at exactly this issue. Below is the call stack and some custom logging I added at the start when promise is undefined. It matches the above analysis.

Promise is:  undefined
channel is:  {}
request.channel name is: customEndpointTelemetry
ctx is:  window:1
request name is  publicLog
  ERR [uncaught exception in sharedProcess]: Cannot read properties of undefined (reading 'then'): TypeError: Cannot read properties of undefined (reading 'then')
    at ChannelServer.onPromise (/Users/billti/src/vscode/out/vs/base/parts/ipc/common/ipc.js:301:21)
    at ChannelServer.onRawMessage (/Users/billti/src/vscode/out/vs/base/parts/ipc/common/ipc.js:266:33)
    at UniqueContainer.value (/Users/billti/src/vscode/out/vs/base/parts/ipc/common/ipc.js:217:73)
    at Emitter._deliver (/Users/billti/src/vscode/out/vs/base/common/event.js:891:26)
    at Emitter._deliverQueue (/Users/billti/src/vscode/out/vs/base/common/event.js:902:22)
    at Emitter.fire (/Users/billti/src/vscode/out/vs/base/common/event.js:925:22)
    at MessagePortMain.fn (/Users/billti/src/vscode/out/vs/base/common/event.js:455:44)
    at MessagePortMain.emit (node:events:513:28)
    at MessagePortMain._internalPort.emit (node:electron/js2c/utility_init:2:367)
    at Object.callbackTrampoline (node:internal/async_hooks:130:17)

[billti]

Note: Turns out the extension was failing for a different reason, but this error led me on a wild goose chase for quite a few hours thinking it was the problem, so would be good to fix :)

[bpasero]

@mroch @billti good findings, would you like to contribute a PR with a fix? Maybe here we should check on the return type and wrap into a Promise if not already one?

vscode/src/vs/base/parts/ipc/common/ipc.ts

Line 1132 in e95fca1

return target.apply(handler, args);