Set MSRV to 1.64.0 in package metadata

[nickelc]

clippy respects the rust version set in the package metadata and wouldn't break the build job for newer rust features.

The current clap version in use dictates 1.64.0.

[dandavison]

Hi @nickelc I trust your changes but would you mind spelling out for me exactly what problem this change is solving?

[nickelc]

First it documents the MSRV for readers and then it limits clippy to only issue warnings for lints that are compatible with the MSRV.

This reduces the possibility of a broken clippy build job and allows the version requirements to be changed deliberately.

For example, the #[derive(Default)] on enum (#1341) was stabilized with 1.62 and I just saw in another project that satisfying clippy bumped the project's MSRV from 1.56 to 1.62.

delta could also be checked against this MSRV with a CI job.

[nickelc]

delta could also be checked against this MSRV with a CI job.

This is how the CI job could look like.

delta/.github/workflows/ci.yml

Lines 111 to 124 in 2c48e35

	msrv:
	name: MSRV
	runs-on: ubuntu-latest
	steps:
	- name: Checkout repository
	uses: actions/checkout@v3
	- name: Get MSRV from package metadata
	id: msrv
	run: grep rust-version Cargo.toml | cut -d'"' -f2 | sed 's/^/version=/' >> $GITHUB_OUTPUT
	- name: Install ${{ steps.msrv.outputs.version }} toolchain
	uses: dtolnay/rust-toolchain@master
	with:
	toolchain: ${{ steps.msrv.outputs.version }}
	- run: cargo check

[dandavison]

How will I know when to update the MSRV?

[nickelc]

How will I know when to update the MSRV?

A build job would allow to check PRs against the MSRV #1343 (comment) and then decide to deliberately bump the MSRV.

[dandavison]

It might well be my lack of familiarity with standard Rust practices but my worry is that this is more moving parts to maintain. When I'm in doubt I sometimes look at how bat and ripgrep do things, as examples of Rust CLI projects, so I'll try to do that.