What does FrozenArray mean in dictionaries?

[saschanaz]

Web Share has this dictionary:

dictionary ShareData {
  FrozenArray<File> files;
  USVString title;
  USVString text;
  USVString url;
};

I guess it has nothing special as a dictionary member or as an argument. Should this be prevented to clarify things?

[annevk]

For an output dictionary it might make sense, but maybe it's best forbidden to align with attributes, indeed.

[domenic]

In general it would be good to align FrozenArray<> more with ObservableArray<>, in order to fix #810. See my previous plan in #810 (comment), which I think still holds and is more or less what I did for ObservableArray<>

[marcoscaceres]

Filed w3c/web-share#165 for Web Share. Also came up in Payment Handler API w3c/payment-handler#372 - I've not followed the ObservableArray discussion, but if we can recommend against people using FrozenArray as per the OP, that would be great (ban it outright, even better so tooling catch these and warn spec Editors).

[foolip]

I noticed a new case of this in web-platform-tests/wpt#28739 and dug up all the current cases of FrozenArray<T> dictionary members:
https://immersive-web.github.io/hit-test/#idl-index
https://immersive-web.github.io/webxr/#idl-index
https://w3c.github.io/orientation-sensor/#idl-index
https://wicg.github.io/shape-detection-api/#idl-index
https://wicg.github.io/shape-detection-api/text.html#idl-index
https://wicg.github.io/ua-client-hints/#idl-index

It looks like in most cases it was just copy-pasted from an interface. While one can make sense of what this means and create the frozen arrays, it does seem kind of pointless. Whenever a dictionary is returned it's a new object, is there really any point in making arrays within frozen?

[foolip]

cc @yoavweiss since WICG/ua-client-hints#228 is very recent, and any rationale might still be in memory :) Or was it just copypasta as it appears?

[amtunlimited]

@foolip WICG/ua-client-hints#228 was me, and yes it was just copypasta. I'll get it fixed soon-ish

[foolip]

Thanks for confirming @amtunlimited!

[domenic]

I think we should prohibit this, FWIW.

[domenic]

Let's roll this into #1399.