It is unclear if [AllowShared] BufferSource is valid

[smaug----]

The spec says
"A type that is not a buffer source type must not be associated with the [AllowShared] extended attribute."
and
"The buffer source types are ArrayBuffer, DataView, and the typed array types."

BufferSource is a union type
typedef (ArrayBufferView or ArrayBuffer) BufferSource;

Yet https://heycam.github.io/webidl/#AllowShared has an example using [AllowShared] BufferSource.

[EdgarChen]

There is some discussion in #827.

[annevk]

See also #342 and #865.

My current thinking on this:

• SharedArrayBuffer should be its own IDL type. We should not overload the ArrayBuffer IDL type to being able to represent ArrayBuffer and SharedArrayBuffer JS types.
• [AllowShared] only applies to ArrayBufferView types.
• We should leave BufferSource as-is.
• We should add SharedBufferSource that also accepts SharedArrayBuffer and that uses [AllowShared] in front of ArrayBufferView.

The outcome of that might well be that [AllowShared] BufferSource is valid as [AllowShared] would end up ignored for ArrayBuffer. I don't have strong feelings about that.

[yuki3]

+1 for Anne's proposal.

Only a nitpick I see is that, considering ArrayBuffer vs SharedArrayBuffer, BufferSource vs SharedBufferSource could be a little confusing. IIUC, the proposal is:

typedef (ArrayBuffer or SharedArrayBuffer or [AllowShared] Int8Array or ...) SharedBufferSource;

Considering ArrayBuffer vs SharedArrayBuffer, the proposed SharedBufferSource does not correspond to SharedArrayBuffer. It corresponds to (ArrayBuffer or SharedArrayBuffer). "Shared" prefix looks confusing to me.

[annevk]

That makes sense, I guess for clarity AllowSharedBufferSource would be better, to indicate it's allowed, but not enforced.
Defined as:

typedef (SharedArrayBuffer or [AllowShared] BufferSource) AllowSharedBufferSource;

I think that works because [AllowShared] ArrayBuffer would end up ignored. Though we could flatten it a bit more if that would be preferred:

typedef (ArrayBuffer or SharedArrayBuffer or [AllowShared] ArrayBufferView) AllowSharedBufferSource;

cc @Constellation

[bathos]

I think that works because [AllowShared] ArrayBuffer would end up ignored.

What makes that ignored? That behavior does make sense to me, but I don’t think it’s what’s currently specified. Type-applicable EAs get distributed to union members unilaterally right now, they aren’t filtered by whether a member does or doesn’t permit that annotation, so I think it would presently imply an error.

[annevk]

You're right, #827 still exists.