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Attempt at https://github.com/servo/servo/issues/16678. At the moment this pulls an external [remove-handle-conv](https://github.com/Xanewok/rust-mozjs/tree/remove-handle-conv) branch for rust-mozjs (removing `FromJSValConvertible` implementation for `HandleValue` and adding one for `*mut JSObject`)
In short, this roots the `sequence<any>` and `sequence<object>` function arguments using `CustomAutoRooter` (introduced in https://github.com/servo/rust-mozjs/pull/382).
As per https://github.com/servo/servo/issues/16678#issuecomment-302224110 the underlying vector contains raw gc thing pointers instead of handles. To do that, this introduces new possible `isMember = "AutoRoot"` value in CodegenRust.py.
The rooted argument is passed to a function wrapped in a `CustomAutoRooterGuard` [RAII root guard](ed5e37a288/src/rust.rs (L586-L588)) (e.g. as `CustomAutoRooterGuard<Vec<JSVal>>`)
I felt quite out of my depth when trying to adapt CodegenRust.py code, so I'd appreciate any help with how can be done better/in a more clean manner.
Also the name `CustomAutoRooterGuard` is quite lengthy, so I'm also open to changing it (`AutoRoot`? `AutoRootGuard`?)
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- [x] These changes fix#16678 (github issue number if applicable).
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Source-Repo: https://github.com/servo/servo
Source-Revision: 989d2fd53267d063212ef3b7b7f13f2402943c4a
ca48a4248a