Remove const_fn_trait_bound feature and update nightly (Mar 2022)

[bradjc]

Pull Request Overview

rust-lang/rust#93827 was merged, so there should soon be a nightly that allows us to remove const_fn_trait_bound feature. It seems like some of the tools we use aren't working right now, but this PR is a placeholder for when we can update to a new enough nightly.

After this, our list of features looks like:

arch/cortex-m/src/lib.rs:#![feature(asm_sym)]
arch/cortex-m/src/lib.rs:#![feature(naked_functions)]
arch/cortex-m0/src/lib.rs:#![feature(asm_sym, naked_functions)]
arch/cortex-m0p/src/lib.rs:#![feature(naked_functions)]
arch/rv32i/src/lib.rs:#![feature(asm_sym, naked_functions)]
boards/esp32-c3-devkitM-1/src/main.rs:#![feature(custom_test_frameworks)]
boards/nano_rp2040_connect/src/main.rs:#![feature(naked_functions)]
boards/opentitan/src/main.rs:#![feature(custom_test_frameworks)]
boards/pico_explorer_base/src/main.rs:#![feature(naked_functions)]
boards/raspberry_pi_pico/src/main.rs:#![feature(naked_functions)]
chips/earlgrey/src/lib.rs:#![feature(naked_functions)]
chips/esp32-c3/src/lib.rs:#![feature(naked_functions)]
chips/litex_vexriscv/src/lib.rs:#![feature(asm_const)]
chips/lowrisc/src/lib.rs:#![feature(const_mut_refs)]
chips/swervolf-eh1/src/lib.rs:#![feature(naked_functions)]
doc/courses/rustconf/application.md:#![feature(alloc)]
kernel/src/lib.rs:#![feature(core_intrinsics)]
libraries/riscv-csr/src/lib.rs:#![feature(asm_const)]
libraries/tock-cells/src/lib.rs:#![feature(const_mut_refs)]

Testing Strategy

travis

TODO or Help Wanted

Need a version of nightly with all valid tools.

Documentation Updated

• Updated the relevant files in /docs, or no updates are required.

Formatting

• Ran make prepush.

[lschuermann]

Pretty cool.

Regarding the tock-registers changes: IIRC this removes all unstable features from the tock_registers crate, which has (a) been requested in #2982 and (b) should allow us to pretty painlessly extract this crate into it's own repository. I've been working on a strategy with @ppannuto on the latter, and would like to -- if possible -- include things such as a solution to #2941 before splitting it out and releasing a tock-registers 1.0. Thus I propose to, after this makes it in, release a tock-registers 0.9.1 with the feature removed as the sole change. It gives us a few more weeks to get in the final changes for 1.0, potentially in its own repository.

[alistair23]

Exciting!

[bradjc]

I ran the script again, seems we are still waiting on rls to work again on nightly.

[bradjc]

Hm, it's not clear to me if anyone is going to fix RLS on nightly. There has been an issue open for a month with no attention: rust-lang/rust#94284

The tracking issue for making rust-analyzer default hasn't been closed, but it seems to indicate the delay in the switchover is procedural and not technical rust-lang/rust-analyzer#4224.

Maybe we just drop RLS and see if anyone notices?

[hudson-ayers]

I am not using RLS and am generally of the opinion that anyone who is would be better off switching to rust-analyzer at this point, so in support of letting it go.

[alistair23]

Agreed!

[hudson-ayers]

bors r+

[bors]

Build failed:

• ci-build (ubuntu-latest)

[lschuermann]

I've rebased this and fixed the additional doc comments. We probably shouldn't wait too long before merging to avoid collisions with other PRs.

[lschuermann]

Given we've already approved and tried to merge this previously, I'd say we just give it another go:

bors r+

[bors]

Build succeeded:

• ci-build (macos-latest)
• ci-build (ubuntu-latest)
• ci-format (ubuntu-latest)
• ci-qemu
• ci-tests (macos-latest)
• ci-tests (ubuntu-latest)