Begin resolving cargo-semver-checks blockers for merging into cargo

[nikomatsakis]

Metadata
Owner(s)	@obi1kenobi
Team(s)	cargo
Goal document	2024h2/cargo-semver-checks

Summary

Design and implement cargo-semver-checks functionality that lies on the critical path for merging the tool into cargo itself.

Tasks and status

• Implementation of cargo manifest linting + CLI (@obi1kenobi)
• Initial design for cross-crate checking (@obi1kenobi)
• Initial design for type-checking lints (@obi1kenobi)
• Discussion and moral support (cargo )

[nikomatsakis]

This issue is intended for status updates only.

For general questions or comments, please contact the owner(s) directly.

[obi1kenobi]

Status update as of September 1.

Key developments: We've laid a lot of the groundwork to make manifest linting possible.

• In preparation for the significant expansion of our CLI, we now have the ability to test how CLI invocations get interpreted internally. We can also now snapshot the output of any CLI invocation over a given workspace, allowing us to proceed with refactoring the implementation without breaking existing use cases.
• We have a concrete design for the expansion of the CLI, and for the Trustfall schema changes that will be necessary to enable manifest linting.

Not blocked on anything. No opportunities to contribute yet, but stay tuned — there will be some in future updates!

[obi1kenobi]

Status update as of September 17.

Key developments: Working prototype of manifest querying.

WIP branch here: https://github.com/obi1kenobi/trustfall-rustdoc-adapter/compare/manifest_querying

An example SemVer lint this enables would be: "a non-nightly, non-underscore-prefixed feature has been removed from the package between releases."

{
    CrateDiff {
        baseline {
            feature {
                feature: name
                    @filter(op: "!=", value: ["$nightly"])
                    @tag
                    @output
            }
        }

        current {
            feature @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
                name @filter(op: "=", value: ["%feature"])
            }
        }
    }
}

# args:
{
    "nightly": "nightly",
    "zero": 0
}

This is SemVer-major because it'll break uses like: my_dep = { version = "1.0", features = ["removed_feature"] }. We're ignoring any features named nightly because community consensus is that such features are unstable — I'll do some more research on other expected-unstable feature patterns in the community before we ship any lints around this.

Not blocked on anything. No opportunities to contribute yet, but stay tuned — there will be some in future updates!

[obi1kenobi]

No major updates to report. Preparing my talk for next week's EuroRust has taken away most of my free time.