Why is MediaPositionState nullable?

[annevk]

This came up in whatwg/webidl#774. Credit: Kagami Sascha Rosylight.

[bzbarsky]

Note that this is not even valid IDL. See whatwg/webidl#774 (comment) and https://bugs.chromium.org/p/chromium/issues/detail?id=997708

[mounirlamouri]

Yeah, I remember being surprised to see optional and nullable. I thought nullable alone may be the right thing and that's how it's implemented in Blink but what I hear is that this actually incorrect and the right solution is to have it optional only. Am I getting this right?

[bzbarsky]

and that's how it's implemented in Blink

That's not valid IDL either, fwiw, and the fact that the Blink bindings allow it is a longstanding issue. :(

The right solution is to have it be optional only if the dictionary has no required members. In that case, all of undefined, null, and Object.create(null) (and in most cases {}) will get treated as an empty dictionary when passed from JS.

[mounirlamouri]

This dictionary has no required members indeed. So I'm not sure if I understand this correctly. Are you suggestion to have optional MediaPositionState or have wording in spec checking whether the dictionary is empty.

[bzbarsky]

If the dictionary has no required members, then per IDL spec the only valid syntax here is:

void setPositionState(optional MediaPositionState state = {});

The prose for setPositionState would then do whatever it does with the MediaPositionState's members being either present or not present.