fix minimal-versions correctness (v0.1.x)

[CAD97]

Essentially a cherry-pick of #2231, but redone by hand.

Tests

• cargo minimal-versions msrv verify -- cargo check --all-features
• cargo minimal-versions msrv verify -- cargo check --no-default-features

Methodology

• cargo update && cargo upgrade --to-lockfile
  • Identify a bug and manually resolve it
• loop; upgrade transitive deps
  • cargo minimal-versions check --all-features
  • Identify failing dep
  • cargo minimal-versions tree -i dep --all-features
  • Find the closest dependency leading to pulling in dep
  • cargo add fixdep --optional to force a more recent more-minimal-versions-correct version
• loop; downgrade to msrv
  • cargo minimal-versions msrv verify -- cargo check --all-features
  • Identify failing dep
  • cargo minimal-versions tree -i dep --all-features
  • Find the version that supports MSRV from lib.rs
  • cargo upgrade dep@msrv

[CAD97]

Three notes:

• This does upgrade deps which are not strictly necessary to upgrade to fix minimal=versions (as did Fix minimal-versions #2231), as upgrading deps one-by-one to fix minimal-versions is much more difficult than downgrading to fix msrv.
• Phantom dependencies on transitive deps were made optional (unlike in Fix minimal-versions #2231) to avoid introducing false dependencies under --no-default-features. This should be done for master as well.
• We might want to have the phantom dependencies rename to __dep so the feature is hidden.

[hawkw]

looks good to me, thanks for working on this!

let's consider addressing the feature renaming and stuff in a follow-up branch.

[hawkw]

what is the explicit .0 doing here? i can't immediately think of a reason it would be needed...is this just a style change?

[CAD97]

Just a style change, yes, as this doesn't impact cargo's behavior

But it does change cargo-upgrade's behavior: cargo-upgrade by default won't increase the precision of dependency specification (and I couldn't find a flag to tell it to do so).

So in order to actually make sure the dependency specifications match what I had in the lockfile, I did a s/"(\d+\.\d+)"/$1.0/g to get cargo-upgrade to make the specifications match the lockfile.

I did try not doing this initially and it wasn't sufficient. Any remaining .0 then is now an explicit note that we're observed to work with .0.