Invalid Web IDL loop between NDEFRecordInit and NDEFMessageInit

[rakuco]

https://heycam.github.io/webidl/#idl-dictionaries says:

The type of a dictionary member must not include the dictionary it appears on. A type includes a dictionary D if at least one of the following is true:

1. the type is D
2. the type is a dictionary that inherits from D
3. the type is a nullable type whose inner type includes D
4. the type is a sequence type or frozen array whose element type includes D
5. the type is a union type, one of whose member types includes D
6. the type is a dictionary, one of whose members or inherited members has a type that includes D
7. the type is record<K, V> where V includes D

#454 introduced a case of 4, 5 and 6, as right now NDEFRecordInit.data can be an NDEFMessageInit, which is a dictionary with a sequence of NDEFRecordInits. This creates a loop that is not allowed by Web IDL and which can cause implementation issues like https://bugs.chromium.org/p/chromium/issues/detail?id=1242274

[kenchris]

External records allow sub-records, so it does make sense that you can create a record with other records inside it. NFC doesn't define any limit of sub records with sub records, but doing more than one or two would be quite rare.

If web idl doesn't allow this, then I don't know how to spec it

[zolkis]

If we need to break the structural definition of recursive data, we can define a function in NDEFRecord to init its data from an NDEFMessageInit. A breaking change :).

[kenchris]

Maybe @littledan or @domenic have ideas here

[reillyeon]

Prior to #454 the data field used the any type instead. This violates the spirit of the WebIDL specification but would give us the opportunity to add a depth limit to the create NDEF message steps because we get to define when and how that arbitrary value is interpreted as an NDEFMessageInit.

[domenic]

Yes, using any or object and doing the conversion in prose with an additional depth-check step seems like a good solution.

[rakuco]

My involvement with this spec is very minimal, so it'd be great if someone could make the required changes here. I can help with the implementation changes later.

[beaufortfrancois]

I'll work on a spec PR in the following days.

[beaufortfrancois]

I've started a spec PR at #621. Please let me know what you think.

[beaufortfrancois]

@rakuco Spec has been updated. See https://w3c.github.io/web-nfc/#creating-ndef-message and #621

[rakuco]

Thank you!