Add a flag to exit with a non-zero status code on warnings

[SamirTalwar]

Description

We can now configure the various levels of each lint option in Cargo.toml. I currently have one that looks like this:

[workspace.lints.clippy]
all = { level = "warn", priority = 0 }
pedantic = { level = "warn", priority = 0 }
# disable some pedantic warnings which feel a little too pedantic
doc_markdown = { level = "allow", priority = 1 }
missing_errors_doc = { level = "allow", priority = 1 }
missing_panics_doc = { level = "allow", priority = 1 }
module_name_repetitions = { level = "allow", priority = 1 }
must_use_candidate = { level = "allow", priority = 1 }
similar_names = { level = "allow", priority = 1 }
wildcard_imports = { level = "allow", priority = 1 }
# these should probably be enabled
default_trait_access = { level = "allow", priority = 2 }
from_iter_instead_of_collect = { level = "allow", priority = 2 }
large_futures = { level = "allow", priority = 2 }
needless_pass_by_value = { level = "allow", priority = 2 }
unnecessary_wraps = { level = "allow", priority = 2 }
unused_async = { level = "allow", priority = 2 }

I want to run Clippy in pre-commit checks and CI too, and in these situations, I want it to fail (exit with a non-zero status code) if any warnings are encountered.

Currently I have two ways of doing this:

1. using something like sed to rewrite Cargo.toml, replacing "warn" with "deny", or
2. using flags to override the lints.

Neither of these seem great. Using sed is error-prone, especially when running it locally in a pre-commit hook, and if I use flags, I have to re-specify all of the "allow" lints, which means I probably have to generate the command-line arguments programmatically.

I would like a command-line argument that tells Clippy to fail on warnings instead. I suggest --exit-with-failure-on-warnings, though you may prefer something more terse.

I am happy to attempt to work on this feature myself, but I would like to discuss it to ensure that the maintainers of Clippy agree in principle first.

If I am missing an obvious way to achieve this, please let me know!

Version

rustc 1.76.0 (07dca489a 2024-02-04)
binary: rustc
commit-hash: 07dca489ac2d933c78d3c5158e3f43beefeb02ce
commit-date: 2024-02-04
host: aarch64-apple-darwin
release: 1.76.0
LLVM version: 17.0.6

Additional Labels

No response

[Alexendoo]

Using --deny warnings is the current recommendation for this, e.g. through RUSTFLAGS

There is a proposal on the cargo side to add a flag for this - rust-lang/cargo#8424

[SamirTalwar]

@Alexendoo, I didn't know that would work with Clippy warnings. Thanks!

This is a good solution for CI but as it's a change to the rustc flags, it requires recompiling all dependencies, which is kind of unworkable for a pre-commit check.

It sounds like the Cargo flag is the proposed solution already though, and reading through it, I get the impression it's intended to only apply to local crates, not dependencies, so I think it will address the above issue.

Do you think this issue should be closed, then, and converted to a comment on the Cargo issue?

[Alexendoo]

You could try cargo clippy -- -D warnings for such a hook, I believe that would avoid recompiling dependencies.

Yeah the cargo issue would be the place to look at for a solution that works everywhere in cargo, but I think that should suit your needs on the clippy side of things.

As an aside priority in [lints] can be negative so you only have to set it for groups, e.g.

[workspace.lints.clippy]
pedantic = { level = "warn", priority = -1 }
# disable some pedantic warnings which feel a little too pedantic
doc_markdown = "allow"
missing_errors_doc = "allow"
# ...