DictionaryMember default [] is rendered as None

[emlun]

For example, see https://www.w3.org/TR/2019/WD-webauthn-2-20191126/#dom-publickeycredentialcreationoptions-excludecredentials, where this markup:

    sequence<PublicKeyCredentialDescriptor>      excludeCredentials = [];

is rendered as:

excludeCredentials, of type sequence<PublicKeyCredentialDescriptor>, defaulting to None

I'm new to the fine details of WebIDL and Bikeshed, but if I understand the specs correctly, [] is a valid default value and should probably be rendered as simply "[]". In that case, the root cause of the issue seems to be here:

https://github.com/tabatkins/bikeshed/blob/2a881f0ee698433d75c6a1555514334adb37d8c7/bikeshed/idl.py#L158-L160

which does not account for that construct.default.value will be None if the default value is [] or {}, in which case the object will have ._open and ._close set instead of .value.

Changing it to this seems to fix the issue, but it doesn't seem like the right solution:

                value = escapeAttr("{0}".format(construct.default.value if construct.default.value else (construct.default._open.symbol + construct.default._close.symbol)))

I'd be happy to contribute a fix if I can get a confirmation that my understanding seems correct, and perhaps some pointers to what might be a better solution. 🙂

[tabatkins]

Huh, interesting. Welp, it's definitely an error, but I'll have to look more into open/close to see what all that covers.

[emlun]

Ok, thanks for confirming! I'll look around some more and see if I can find something that seems like a good solution.

What I found is that the relevant values are set here in Default:

https://github.com/tabatkins/bikeshed/blob/2a881f0ee698433d75c6a1555514334adb37d8c7/bikeshed/widlparser/widlparser/productions.py#L1108-L1111

which is called from here in DictionaryMember:

https://github.com/tabatkins/bikeshed/blob/2a881f0ee698433d75c6a1555514334adb37d8c7/bikeshed/widlparser/widlparser/constructs.py#L1043-L1050