Array proxies as keys?

[inexorabletash]

I noticed that this throws in both Chrome and Firefox:

const k = [1,2,3];
const p = new Proxy(k, {});
indexedDB.cmp(k, p);

In Chrome, at least, the proxy fails an internal "is this an array?" check.

In the spec convert a value to a key calls ECMAScript's IsArray which would seem to return true for array proxies.

At the very least, we don't have tests.

Should we update the spec to exclude proxies, e.g. replacing "if IsArray(input)" with "if input is an Array exotic object"?

Alternately, should array proxies be supported? What are the consequences of allowing these? Would the value→key conversion algorithm potentially blow up in more places?

[asutherland]

The algorithms where we clone a value already forbid proxies thanks to step 23 of StructuredSerializeInternal (https://html.spec.whatwg.org/#structuredserializeinternal) which prevents use of proxies.

It makes sense to me to also forbid proxies where we directly invoke algorithms without first performing the clone step.

(Also, Firefox/Gecko is a hard no on supporting proxies in IndexedDB were that not already the case!)

[inexorabletash]

SGTM. I'll put up a spec PR and wpt PR, time permitting, changing the text to the exotic Array object check.