[feature] Support additional install args for Rust toolchain bins

[JakubWasilczyk-Alias2k]

Is your feature request related to a problem? Please describe.

The Rust toolchain bins list only takes a crate name and version, like diesel_cli@2.3.9. I can't pass any flags to the install command.

That's a problem for crates like diesel_cli, whose default features pull in postgres, mysql and sqlite. Building it needs all three client libraries installed, even though we only use postgres. The install command we actually want is:

cargo install diesel_cli@2.3.9 --no-default-features --features postgres

There's no way to write that in .moon/toolchain.yml, so we install diesel_cli by hand and it stays outside of moon.

Describe the solution you'd like

Let a bin entry carry extra arguments:

rust:
  bins:
    - bin: 'diesel_cli@2.3.9'
      args: ['--no-default-features', '--features', 'postgres']

moon appends args to the install command. It would also be nice if changing args triggered a reinstall instead of being skipped because the binary already exists.

Describe alternatives you've considered

• Installing it manually or in a separate task. Works, but every dev and CI runner has to remember it, and moon doesn't know about the tool.
• Installing every backend. Means every machine needs libpq, libmysqlclient and libsqlite3 for nothing.
• Relying on prebuilt binaries from cargo-binstall. Those ship with whatever features the author picked, so non-default feature sets aren't possible.

Additional context

Other crates would benefit too, for example sqlx-cli with --no-default-features --features rustls,postgres. Might be worth skipping binstall and going straight to cargo install whenever args is set, since binstall's handling of feature flags isn't consistent.

moon version: 2.5.3
OS: MacOS