Allow for global objects with a mutable prototype chain

[Ms2ger]

This is required to define the ShadowRealm global object in IDL.

• At least two implementers are interested (and none opposed):
  • N/A, part of ShadowRealm.
• Tests are written and can be reviewed and commented upon at:
  • Add a test for the mutability of the ShadowRealm global prototype chain web-platform-tests/wpt#43756
• Implementation bugs are filed:
  • Chromium: …
  • Gecko: …
  • WebKit: …
  • Deno: …
  • Node.js: …
  • webidl2.js: …
  • widlparser: …
• MDN issue is filed: N/A
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

---

Preview | Diff

[annevk]

Thanks, pretty close now. (I'm trusting the JS bits as you probably know that better than me.)

[annevk]

Let's give some time for others to comment, but to me this seems good to go.

I guess there's a question of how much we want to wait for implementer interest for an infrastructure change. @domenic thoughts?

[domenic]

I guess there's a question of how much we want to wait for implementer interest for an infrastructure change. @domenic thoughts?

In general I'm supportive of not waiting too much. (E.g. it seems annoying to me that #1353 is stalled on that.) But the overall fate of ShadowRealm seems a bit unclear to me, given its regression to stage 2, so I'm a bit hesitant about making a bunch of ShadowRealm-related changes to our specs.

But, it's probably fine, as long as we're good about reverting if a proposal gets withdrawn. That's what we did for, e.g., #924.

[Ms2ger]

ShadowRealms was reverted to stage 2 because the web-side specifications were not ready; this PR is one of the blockers to advance to stage 3 again.

[annevk]

@Ms2ger would you be willing to file the implementation bugs for this and update OP afterwards? I'm thinking primarily of the tooling-related projects. Browsers will get there as part of ShadowRealm.