Release blog post - v0.16.0 about cargo-msrv HOT 1 OPEN

December release

Override rustup run commands

By default, the Rustup run command used to test whether a toolchain is compatible, is rustup run <toolchain> cargo check. If you wanted to use another command, you could already use cargo msrv -- <my command>, e.g. cargo msrv -- cargo build. This is necessary for example if you rely on a version of cargo which does not yet have cargo check built in. Then, you could run both: cargo msrv --min 1.16 and cargo msrv --max 1.15 -- cargo build, but this gets old, fast.

From cargo-msrv v0.16 it is also possible to override the compatibility check commands used. To do this, specify the following overrides in your Cargo.toml:

[[package.metadata.msrv.override]]
runner = "rustup-run"
version_req = "<1.17"
compatibility_check = "cargo build"

NB: The combination runner and version_req must be unique. Also note that the version req follows the semver::VersionReq, spec with the following limitation: cargo-msrv only supports stable Rust releases.

By default, from this cargo-msrv release, we will override the compatibility check for Rust toolchains released prior to Rust 1.16 (cargo check became available from Cargo 1.16).

The precedence of overrides is as follows:

• Granular override defined in the Cargo.toml >
• Global override specified via remainder CLI arguments ( cargo msrv -- <cmd>) >
• Default compatibility check override >
• Default compatibility check

Note that running two or more different commands (e.g. cargo build vs cargo check) does mean that you test your project for compatibility in different ways, which may not be consistent with each other.

Since it is unlikely that many people are still using a Rust toolchain before Rust 1.16 (released in 2017, on March 16th), the impact of the default override should be minimal.