Migrate from lazy_static to once_cell

[jaudiger]

lazy_static!, while a declarative macro, is a macro nonetheless. It can add quite a bit of additional compilation time cost. once_cell::sync::Lazy does the same thing with generics, and can be used more flexibly (i.e. non-static lazily initialized values), and has been proposed to be added to std: https://github.com/rust-lang/rfcs/pull/2788.

Famous Rust projects already did the transition, such as:

• https://github.com/tokio-rs/tokio/pull/3187
• https://github.com/tokio-rs/tracing/pull/2147

[lucab]

Thanks for the report. Sounds like a good idea! I'll be happy to review a patch doing this if anybody wants to tackle it.

[jaudiger]

Hi @lucab, thanks, I just opened a PR for it !