Specify MSRV instead of fixing the toolchain

[Nashtare]

Description

Specifying a rust-toolchain file fixes the Rust version being used, while we should rather specify an MSRV instead, as is the rust-version field of Cargo.toml intended to be.

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works

[Nashtare]

I'm not sure why the CI for code-coverage is failing, it shouldn't. The error is the following:

Run cargo tarpaulin --verbose --engine llvm --release --out Xml
error: invalid value 'Xml' for '--out [<FMT>...]'

I've noticed it failing on other repos as well (for instance https://github.com/toposware/cheetah), though not really blocking.

[sebastiendan]

Swapping my review with Simon's as I think he can be of much greater value here

[Nashtare]

@sebastiendan Sure thing! Although the CI check being red is a bit ugly. As we'll publish this on crates.io at some point, we'll probably want to address it soon. But non-blocking for this particular PR.

[dvdplm]

Setting an MSRV without testing it in CI is not very useful. If it's truly meaningful to commit to a MSRV I think the project README should state the policy:

• how long do we guarantee the current MSRV?
• backporting policy (we don't backport security patches to the MSRV I'd say, but we should state this publicly)
• when we update the MSRV, how is this communicated? What is the lead time?

Note that committing to a MSRV means that changing it is a breaking change in semver speak, so it means releasing a new major version.

IMO committing to an MSRV is not something we should take lightly.

[dvdplm]

Run cargo tarpaulin --verbose --engine llvm --release --out Xml

Speculation: perhaps it should be --out xml? And it works for macos users because the FS is case insensitive?

[Nashtare]

Speculation: perhaps it should be --out xml? And it works for macos users because the FS is case insensitive?

Perhaps, though I'm confused why it was working in the first place then.

Regarding the MSRV comment, I don't really have an objection to not setting a MSRV and just relying on the latest stable, it just felt more proper to have it declared (and I think as a general rule if every crate was specifying their MSRV this would definitely help the ecosystem) but I'll leave the experts decide here 🙂
@Freyskeyd Do you have any opinion?

[Nashtare]

Closing in favor of #9.