Do not require 'static for obtaining reflection information.

[oli-obk]

tracking issue #142577

This does not affect the stable TypeId::of, as that has its own 'static bound.

But it will allow obtaining TypeIds for non-static types via the reflection API. To obtain such a TypeId for any type, just use Type::of::<(T,)>().kind to extract the first field of a tuple.

This effectively reintroduces #41875, which @rust-lang/lang decided against allowing back in 2018 due to lack of sound use cases. We will thus need to have a T-lang meeting specifically about TypeId for non-static types before stabilizing any part of reflection (in addition to T-lang meetings about reflection in general). I'm adding an explicit point about this to the tracking issue.

cc @scottmcm @joshtriplett @9SonSteroids @SpriteOvO @izagawd @BD103

[rustbot]

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @lcnr

[rustbot]

r? @Mark-Simulacrum

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[lcnr]

But it will allow obtaining TypeIds for non-static types via the reflection API. To obtain such a TypeId for any type, just use Type::of::<(T,)>().kind to extract the first field of a tuple.

This effectively reintroduces #41875, which @rust-lang/lang decided against allowing back in 2018 due to lack of sound use cases. We will thus need to have a T-lang meeting specifically about TypeId for non-static types before stabilizing any part of reflection (in addition to T-lang meetings about reflection in general). I'm adding an explicit point about this to the tracking issue.

Don't have much capacity and going to unsubscribe from this PR, but rly, we should readd non_static_type_id. It is incredibly useful 🤣 it allows soundly going from T without a static bound to types without free regions

[theemathas]

Of note, the typeid crate already implements a hacky way to get a TypeId representing a non-'static type. The crate has a lot of downloads.

[Mark-Simulacrum]

r=me unless we want T-lang/libs-api/xxx FCP or similar.

[oli-obk]

Nope. It's entirely unstable and the point of this experiment is to demonstrate use cases and problematic situations, so now we can explore the latter, too

@bors r=Mark-Simulacrum

[rust-bors]

📌 Commit 3339b06 has been approved by Mark-Simulacrum

It is now in the queue for this repository.