1455179 - Don't warn about undefined properties when destructuring with default values

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P3)

Description

[Kris Maglione [:kmag]]

These warnings come up all the time in our test output. When we destructure with a default value for a missing property, e.g.:

  let obj = {};
  let {foo = 0} = obj;

We get an undefined property warning for `obj.foo`, even though we provide a default value for it. The NativeObject Detecting checks should handle this case, and treat that as a valid detection access.

Comment 1

[Kris Maglione [:kmag]]

Attachment: Bug 1455179: Support destructuring with default values in undefined property detection checks.

Review commit: https://reviewboard.mozilla.org/r/237866/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/237866/

Comment 2

[Nicolas B. Pierron [:nbp]]

Jason, do you think we should ignore the "undefined property" warnings when destructing objects?

Comment 3

[André Bargull [:anba]]

If this patch lands, bug 1300416 can be closed, too.

Comment 4

[Kris Maglione [:kmag]]

(In reply to Nicolas B. Pierron [:nbp] {backlog: ~36} from comment #2)
> Jason, do you think we should ignore the "undefined property" warnings when
> destructing objects?

To be clear, this only ignores properties that have default values. I.e.,

  let {foo = 0, bar} = {};

will warn for `bar` but not `foo`.

Comment 5

[Nicolas B. Pierron [:nbp]]

Comment on attachment 8969150 [details]
Bug 1455179: Support destructuring with default values in undefined property detection checks.

https://reviewboard.mozilla.org/r/237866/#review244164

Thanks for this patch, it does fix some missing corner cases implied by the original comments.

Comment 6

[Kris Maglione [:kmag]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/219afe052ae3a80b1da61d60ade56d73af0b0ca2
Bug 1455179: Support destructuring with default values in undefined property detection checks. r=nbp

Comment 7

[Andreea Pavel [:apavel]]

https://hg.mozilla.org/mozilla-central/rev/219afe052ae3

Comment 9

[Jason Orendorff [:jorendorff]]

Too late, but yes, this was the right call.