`const_fn` weirdness on v0.9.0

[reinvantveer]

Hi, thank you for sharing all this awesomeness. It's truly amazing.

Since lock_api dropped the const_fn attribute, in v0.4.4 commit Amanieu/parking_lot@aea1350 I'm running into compile trouble using the use_spin_nightly feature. I'm using a custom-built 1.52.0-dev nightly Rust/Cargo and LLVM toolchain with Motorola 68000 family support, which I play around with to program for the Sega Megadrive. It's a blast.

dependency:
linked_list_allocator = { version = "0.9.0", default-features = false, features = ["use_spin_nightly"] }

I get:

error[E0723]: trait bounds other than `Sized` on const fn parameters are unstable
   --> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/lock_api-0.4.4/src/rwlock.rs:348:6
    |
348 | impl<R: RawRwLock, T> RwLock<R, T> {
    |      ^
    |
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable

I'm fairly new to this. I haven't done any systems programming before, and some elevator-music equivalent of Rust programming. Any idea on how to get around this? Thanks in advance for any pointers!

[phil-opp]

This sounds like you need to update your Rust nightly version. If that's too difficult for you, you could try to add an lock_api = "=0.4.3 dependency to your crate as a workaround, then cargo should use that version for linked_list_allocator as well.

[reinvantveer]

Thanks for the response! That resolves in a different compile error:

error[E0432]: unresolved import `core::sync::atomic::AtomicUsize`
  --> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/lock_api-0.4.3/src/remutex.rs:19:20
   |
19 |     sync::atomic::{AtomicUsize, Ordering},
   |                    ^^^^^^^^^^^ no `AtomicUsize` in `sync::atomic`

Any suggestions on this?

[reinvantveer]

I did find this: Amanieu/parking_lot#277 but I'm not sure it applies here. I can import core::sync::atomic::AtomicUsize without problem in my lib.rs. Can't think of a reason why https://github.com/Amanieu/parking_lot/blob/lock_api-0.4.3/lock_api/src/remutex.rs#L19 would pose an issue.

[phil-opp]

Are you sure that you can import it in your lib.rs for the same target?

[reinvantveer]

Ah. Double-checking and I see it doesn't, my bad. It just was not the first AtomicUsize for the compiler to stumble over. I think with pinning lock_api = "=0.4.3" in my own cargo toml is enough information to go on for now. Thanks!