Migration Guide: v0.19 to v0.20

Cargo MSRV 0.20.0 adds improved Cargo workspace support and tries to more strictly determine up front whether a project is a cargo project or not (called bare). This is cargo-msrv's mode.

If you only run cargo-msrv on a single crate, or are in a bare project (i.e. a project without Cargo), or didn't use json or minimal output formats, you probably won't need to do anything but be aware that cargo-msrv may run on a workspace iso a single package by default now.

Workspace flags come after the subcommand

In v0.19, the --workspace, --package and --exclude flags had to be given before the subcommand, for example cargo msrv --workspace find. They now come after the subcommand (like cargo):

# v0.19
cargo msrv --package $crate_name find

# v0.20
cargo msrv find --package $crate_name

The cargo workspace flags are accepted by find, verify, show and set. Please refer to the Cargo Workspace page for more on workspaces and how cargo-msrv selects packages.

Subcommands run for each selected package

In v0.19, cargo msrv find and cargo msrv verify ran once, for the crate root. In v0.20, find, verify, show and set run once for each selected package. In a workspace, this means you may now get a result for more than one package.

Consequently:

cargo msrv find --write-toolchain-file now writes the toolchain file to the workspace root, since it applies to the whole workspace. It writes the highest MSRV it found.
cargo msrv find --ignore-lockfile and cargo msrv verify --ignore-lockfile now temporarily move the lockfile of the workspace.
cargo msrv set and cargo msrv find --write-msrv no longer overwrite a rust-version which is inherited from the workspace (rust-version.workspace = true). Use cargo msrv set --workspace-msrv to set the workspace MSRV instead.
When a custom check command is used, the project is still checked once, as a whole. NB: This may change in a future release, please feel free to discuss feedback on GitHub's discussions or the issue tracker :)

New errors

When cargo-msrv detected a workspace, it previously just ignored it. Now it tries to more strictly differentiate between the mode it is in (cargo or bare). Options which don't make sense outside of the cargo mode are now reported as errors:

Using --workspace, --package, --exclude or --manifest-path outside a Cargo project.
A Cargo project for which cargo metadata fails, for example because its Cargo.toml can't be parsed.

Rust versions are parsed more strictly

Rust versions now reject leading zeros, like Cargo. For example, 1.05 is no longer accepted (use 1.5 instead).

The package.metadata.msrv key, which can be used as a fallback on Rust versions which don't support package.rust-version yet, now only accepts full (three component, e.g. 1.56.0) or short (two component, e.g. 1.56) versions, like Cargo's rust-version.

Building cargo-msrv from source

Only relevant if you build cargo-msrv from source:

The rust-changelog release source is now behind the rust-releases-changelog-source Cargo feature. It is enabled by default, so this only matters if you build cargo-msrv with --no-default-features.

Output formats

json

Refer to the JSON output format page for the complete descriptions of the events.

Selected packages

The selected_packages event has been replaced by the context_finalized event. Besides the selected packages, it also reports whether cargo-msrv runs in a Cargo project, and whether that project is a workspace. Where selected_packages only reported the detected and selected Cargo packages, we now instead send one event which reports details about the context the program will run with (the context provides "resolved" configuration and environment values. If you use cargo-msrv as a library instead of a CLI, you could do all the work of gathering config values yourself and only call cargo-msrv with just context values).

While the actual context does contain more than just the mode, workspace or packages, the event is currently limited to these. If you feel that more values from the context should be reported, please open an issue or topic on the discussion forum.

Previously:

{
  "type": "selected_packages",
  // `null` when not in a Cargo project
  "package_names": [
    {
      "name": "a",
      "path": "/workspace/a/Cargo.toml"
    }
  ]
}

Replacement:

{
  "type": "context_finalized",
  "project": {
    "mode": "cargo",
    "workspace": true,
    "packages": [
      {
        "name": "a",
        "path": "/workspace/a/Cargo.toml"
      }
    ]
  }
}

When not in a Cargo project, project.mode is bare, and the workspace and packages fields are absent.

Results for each package

Since subcommands now run for each selected package, you may receive more than one subcommand_result event. Each of event now has a new package field, which tells you which package the result is for.

{
  "type": "subcommand_result",
  "subcommand_id": "show",
  "package": {
    "name": "a",
    "path": "/workspace/a/Cargo.toml"
  },
  "result": {
    "version": "1.56.0",
    "manifest_path": "/workspace/a/Cargo.toml"
  }
}
{
  "type": "subcommand_result",
  "subcommand_id": "show",
  "package": {
    "name": "b",
    "path": "/workspace/b/Cargo.toml"
  },
  "result": {
    "version": "1.58.0",
    "manifest_path": "/workspace/b/Cargo.toml"
  }
}

The checks of find and verify for a single package are now wrapped in the new scoped check_package event.

minimal

When the mode is cargo and cargo-msrv detected a workspace with more than one package, cargo-msrv now outputs the name of the package and followed by the found MSRV.

a 1.56.0
b 1.58.0

When there is a single package, the output is unchanged, e.g.:

1.56.0

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