# shelbi msrv-check

Build a Rust workspace on its declared minimum Rust version, as a zen.checks.local entry that catches MSRV breaks before handoff.

```text
shelbi msrv-check [OPTIONS]
```

`shelbi msrv-check` builds the Rust workspace in the current directory on the
minimum Rust version it declares (the `rust-version` in `Cargo.toml`), the way a
typical CI `msrv` job does:

```bash
cargo +<rust-version> check --workspace --all-targets --locked
```

It's meant as a [`zen.checks.local`](/docs/configuration/project#zen) entry on Rust
projects. A stable-toolchain build won't notice a lockfile change that pulls in
a dependency needing a newer Rust than the declared minimum; this catches it
before handoff instead of only in CI.

It reads `rust-version` from the nearest `Cargo.toml` at or above the current
directory. If the toolchain isn't installed it installs it once with `rustup`.
It never fails for reasons unrelated to the code:

- no `rust-version` found, `rustup` missing, or a toolchain that can't be
  installed (offline, for example) prints a warning on stderr and exits `0`
  (a skip);
- a real MSRV break (the check ran and `cargo` failed) exits with `cargo`'s
  non-zero status.

| Variable | Effect |
| --- | --- |
| `SHELBI_SKIP_MSRV_CHECK=1` | Skip the check entirely (exit `0`). For a host that intentionally doesn't provision the MSRV toolchain. |
| `SHELBI_MSRV_NO_INSTALL=1` | Never install a missing toolchain; skip instead. The check still runs where the toolchain is already installed. |

`msrv-check` has no flags of its own beyond the global `--root` and
`-p, --project`, which it doesn't use.

## Examples

Add it to a project's local Zen checks:

```yaml
zen:
  checks:
    local:
      - shelbi msrv-check
```

Run it by hand from the repository root:

```bash
shelbi msrv-check
```

## See also

- [Project configuration](/docs/configuration/project#zen): where `zen.checks.local`
  is set.
- [Zen Mode](/docs/concepts/zen-mode): when local checks run.