Internal method invariants vague about exceptions

[annevk]

A number of internal methods can throw per HTML, but https://tc39.github.io/ecma262/#sec-invariants-of-the-essential-internal-methods is not clear on whether that is allowed. (Despite it already being implicitly allowed, e.g., OrdinaryDelete invoking [[GetOwnProperty]] with a ? in front of it.)

This came up in whatwg/html#1726 as cross-origin [[Delete]] always throws in implementations, even outside "strict mode", and therefore cannot simply return false.

[claudepache]

All internal methods may throw: that can happen notably, but not exclusively, when user-defined code is triggered and throws (Proxies, user-defined accessors, etc.). And https://tc39.github.io/ecma262/#sec-invariants-of-the-essential-internal-methods applies only when the internal method returns nonabruptly: maybe that should be said explicitly?

[annevk]

It would help me, I think I got myself confused a few times now reading that section.

[jmdyck]

(Just noticed this issue.) See #1537 for related discussion, and #1539 which should resolve @annevk's original concern.

[allenwb]

Note that 6.1.7.2 says:

An internal method implicitly returns a Completion Record, either a normal completion that wraps a value of the return type shown in its invocation pattern, or a throw completion.

[jmdyck]

(Yes, but also note that it didn't say that when @annevk opened this issue.)

[allenwb]

We ES6, at approximately the same place said:

An internal method implicitly returns a Completion Record as described in 6.2.2.

The explicit case would have been covered by being explicit.

[jmdyck]

Yup, and saying that it returns a Completion Record wasn't enough to answer the original question.

[annevk]

Thanks for fixing this @jmdyck!