1555464 - Turn the pref for public fields on by default

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Ashley Hauck [:khyperia]]

There's not really any actual work to do here: this is a tracking bug for the release of public fields.

See the depends-on list of bug 1499448 to assess what remaining work there is. The tree view is particularly helpful.

Comment 1

[Jason Orendorff [:jorendorff]]

Attachment: Bug 1555464 - Part 1: Turn the pref for public fields on by default. r?khyperia

Comment 2

[Jason Orendorff [:jorendorff]]

Attachment: Bug 1555464 - Part 2: Enable fields by default in the JS shell. r?khyperia

Depends on D34638

Comment 3

[Jason Orendorff [:jorendorff]]

Public fields are a JavaScript language feature that's used in classes.

class Car {
  make = "Ford";
  model = "Prefect";
  wheels = [0, 0, 0, 0];
}

let myCar = new Car;  // {make: "Ford", model: "Prefect", wheels: [0, 0, 0, 0]}

We implement only the public fields described in this proposed specification. No private fields yet.

Comment 4

[Nicolas Chevobbe [:nchevobbe]]

Do you know if there should be some devtools support for this?
I can't think of anything specific, but maybe I'm missing something.
Thanks

Comment 5

[Jason Orendorff [:jorendorff]]

Try

• stepping over the class Car declaration;
• stepping into new Car and stepping over each assignment

and see if the behavior is reasonable.

Unfortunately, I think it will probably be ugly and hard to fix. :-\

Comment 6

[Jason Orendorff [:jorendorff]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=4a8e776762d22867691ea1f93630e540596eff9a

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d7e33c843b24
Part 1: Turn the pref for public fields on by default. r=khyperia
https://hg.mozilla.org/integration/autoland/rev/8227f5fbbe20
Part 2: Enable fields by default in the JS shell. r=khyperia

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9e789088540d
Part 2: Enable fields by default in the JS shell. r=khyperia

Comment 9

[Razvan Maries]

https://hg.mozilla.org/mozilla-central/rev/9e789088540d

Comment 10

[Gary Kwong [:gkw] [:nth10sd] (NOT official MoCo now)]

Jason/Ashley, is --disable-experimental-fields worth testing? (if so, it should probably be in fuzz-flags.txt)

Sidenote, --enable-experimental-fields got removed here...

Comment 11

[Ashley Hauck [:khyperia]]

In my opinion, probably not? I'm not 100% sure of why we keep the flag in, I'm assuming it's a last resort backup plan to disable things if everything explodes? So it's not going to stay relevant for long, once the feature has rode all the way to release.

Comment 12

[Jason Orendorff [:jorendorff]]

Agreed, it's only there as a last resort backup plan.

I would not bother fuzz-testing this.

Comment 13

[Jason Orendorff [:jorendorff]]

Gary, note that I'm going to do the same thing to --enable-experimental-await-fix later this week, over in bug 1558971.

Comment 14

[Gary Kwong [:gkw] [:nth10sd] (NOT official MoCo now)]

Got it, thanks! (I won't bother with these flags then, just clarifying...)

Comment 15

[Florian Scholz (Open Web Docs)]

Compat data updated: https://github.com/mdn/browser-compat-data/pull/4711
Added to release notes: https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/69#JavaScript
Classes page mentions it: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes#Field_declarations
New page on class elements lives here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Class_elements