The return value for update() is wrong in WebIDL

[philipwalton]

The current WebIDL for the ServiceWorkerRegistration is incorrect; it shows update() returning Promise<void>.

I believe this is a mistake since implementations all return the registration object, and the update() algorithm says to return the registration as well.

[saschanaz]

Indeed it returns an object per the Resolve Job Promise algorithm:

2. If job’s job type is either register or update, set convertedValue to the result of getting the service worker registration object that represents value in job’s client.
3. Else, set convertedValue to value, in job’s client’s Realm.
4. Resolve job’s job promise with convertedValue.

But:

I believe this is a mistake since implementations all return the registration object

AFAICT Gecko and WebKit returned undefined since forever.

[yoshisatoyanagisawa]

Let me check what is written in WebIDLs.
Chromium:

[CallWith=ScriptState, RaisesException] Promise<ServiceWorkerRegistration> update();

(https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/modules/service_worker/service_worker_registration.idl;l=26;drc=047c7dc4ee1ce908d7fea38ca063fa2f80f92c77)

Gecko:

[Throws, NewObject]
Promise<undefined> update();

(https://github.com/mozilla/gecko-dev/blob/fefa0c86cf24e6afa9f4dbb3823d4d16b2713dc7/dom/webidl/ServiceWorkerRegistration.webidl#L28)

WebKit:

[NewObject] Promise<undefined> update();

(https://github.com/WebKit/WebKit/blob/f8eb4cf035d529c6e55ebfd28c92fdc9468981d5/Source/WebCore/workers/service/ServiceWorkerRegistration.idl#L46)

As @saschanaz pointed out, Gecko and WebKit returns Promise<undefined>.
However, although the WebIDL looks invalid, Chromium seems to follow the step by step description in Resolve Job Promise algorithm.

If mismatch of WebIDL and Resolve Job Promise algorithm matters, adjusting the WebIDL can be a choice. What do you think?

[saschanaz]

Depends on whether there's enough implementation interest for that, otherwise I'd vote for following the majority. cc @asutherland

[asutherland]

According to https://wpt.fyi/results/service-workers/service-worker/update-result.https.html?label=experimental&label=master&aligned all implementations are actually returning a ServiceWorkerRegistration which is definitely what Gecko is doing despite what our .webidl file says.

For clarity, this is the check in update-result.https.html:

  let result = await reg.update();
  assert_true(result instanceof ServiceWorkerRegistration,
              'update() should resolve a ServiceWorkerRegistration');
}, 'ServiceWorkerRegistration.update() should resolve a registration object');

So I think we should update the WebIDL in the spec to reflect that a ServiceWorkerRegistration is returned and WebKit and Gecko should fix our in-tree .webidl files.

[annevk]

Implementations not actually enforcing validity of this IDL construct through asserts or some such seems like a problem as well here. Separate, but still.

[annevk]

Fixed by #1767.