As I've written before[1], more than a year ago Rust on AVR went into the weeds because of bugs in LLVM.
I made a workaround[2], but it was far from ideal - and if it's been frustrating for me, I'm sure it's been a complete barrier to many even getting started with AVR on Rust.
Anyway, all that has now changed, thanks to Patryk27[3], who has managed to merge the necessary patches into the Rust master, so now the regular Rust `nightly` toolchain builds for AVR again. Hurrah, and the inaugural (and possibly ultimate) 'Hero of the Week' award goes to Patryk :-).
1: /posts/2021-10-09-the-day-rust-on-avr-stood-still.gmi
2: https://gitlab.com/snowgoonspub/rust-avr-nightly-builder
3: https://github.com/Patryk27
--------------------