ci: test minimal version of dependencies

[caspermeijn]

Use cargo minimal-versions to check whether the minimal specified versions dependencies successfully compiles.

As this repo has no Cargo.lock, CI will always test with the newest compatible dependency versions. This new job will check oldest compatible dependency version as well.

This requires unstable nightly feature minimal-versions, but they abstracted away by cargo-minimal-versions project.

prost uses the same job for several months: https://github.com/tokio-rs/prost/blob/21208abf667313866f79d3d1438310c4dc20bdff/.github/workflows/ci.yml#L168-L176

[tomhoule]

Are you able to see the CI output to iterate on this?

[caspermeijn]

Are you able to see the CI output to iterate on this?

So I have been a bit dumb and just committed this CI job without testing. I will look into what dependencies need to change to make this work and add them as separate commits in this PR.

[caspermeijn]

I have not been able to make this work. Some of the transient dependencies have wrong minimal dependencies. I have found a few crates where the minimal dependencies have been fixed in the latest version, but that doesn't help because we want to support the older version.

My conclusion is: a CI job for minimal version is not feasible as long as reqwest 0.11 is in the dependency list.