Test Clippy Lint

[cramertj]

It'd be really helpful for rust-lang/rust#49000 (comment) to be able to find places in the ecosystem that trigger the clippy lint added in rust-lang/rust-clippy#3344. Would it be possible to add a feature to crater to allow running with a clippy warning set to deny-by-default?

[cramertj]

cc @pietroalbini who mentioned they didn't think this would be too hard to add when I spoke with them on discord.

[pietroalbini]

Crater already supports denying lints (with rustflags=-Dlint_name), so the only thing that needs to be added is executing cargo clippy.

That should be implemented as a new experiment mode called clippy with a corresponding task step in the runner. Once you add the variants to the two enums fixing the errors emitted by the compiler should be enough to implement the mode.

Since clippy is not installed by default you should also install it at the start of the runner (only when the experiment mode is clippy). Adding a method like toolchain.install_rustup_component("clippy") to do that would be awesome.

Also, adding a test to minicrater would be awesome!

If you want to work on this issue please comment on it so other contributors know it's taken. And if you need some help or you get stuck please reply here or ask on the #crater channel on Discord!

[ecstatic-morse]

I just started working on this. PR to come shortly.

[ecstatic-morse]

@cramertj, This should now will soon be possible using something like:

@craterbot run name=clippy-test-run mode=clippy start=stable end=stable+rustflags=-Dclippy::your_lint_here

[pietroalbini]

I didn't have time to deploy the changes yet.

[ecstatic-morse]

Sorry! I don't understand how bors works I guess.

[pietroalbini]

The changes are merged by bors on the master branch, but unfortunately deploying them on the servers is still a manual process :(

[pietroalbini]

Now it's deployed!

[ecstatic-morse]

@pietroalbini

Unfortunately, denying clippy lints with cargo via RUSTFLAGS=-Dclippy::lint causes a build failure for crates with a build.rs, so this isn't terribly useful at the moment 😣. Invoking cargo clippy -- -Dclippy::lint succeeds as expected.

I'm not sure how to proceed here. Perhaps this should be fixed in cargo or clippy? Otherwise we could pass flags to rustc without using the environment variable, or strip anything that looks like a clippy lint out before setting RUSTFLAGS.