cargo returns outdated warnings

[matthiaskrgr]

code:

fn main() {
    let a = 0;
}

compiles:

$cargo clippy
    Checking warn v0.1.0 (/tmp/warn)
warning: unused variable: `a`
 --> src/main.rs:2:9
  |
2 |     let a = 0;
  |         ^ help: consider prefixing with an underscore: `_a`
  |
  = note: `#[warn(unused_variables)]` on by default

Suppressing the warning via cli parameters does no longer work until the project is rebuilt from scratch:

$cargo clippy -- -Aunused_variables
warning: unused variable: `a`
 --> src/main.rs:2:9
  |
2 |     let a = 0;
  |         ^ help: consider prefixing with an underscore: `_a`
  |
  = note: `#[warn(unused_variables)]` on by default

    Finished dev [unoptimized + debuginfo] target(s) in 0.00s

cargo 1.42.0-nightly (9d32b7b01 2020-01-26)

[aleksator]

Isn't it an issue with clippy so should be filed against that?
https://github.com/rust-lang/rust-clippy

[ehuss]

This is a known issue that will be fixed by #7533.

You can use cargo clippy-preview on nightly to avoid this for now.

[aleksator]

Triage: the PR #7533 has landed, but the issue persist.

[ehuss]

To be clear, there's a second part where clippy will need to be updated to use the new functionality. There is a rough outline here.

[aleksator]

Seems like there is some related ongoing work over here.

[ehuss]

Oh, I think I misunderstood the original request here, which is specifically around changing the args passed to clippy (like -Aunused_variables). Indeed these are not tracked in the fingerprint or hash (cargo-clippy hides them via __CLIPPY_HACKERY__).

I don't offhand have ideas on how to improve that. Probably clippy could pass those via something like RUSTFLAGS and Cargo could be better about including rustflags in the hash or fingerprint.

[Emilgardis]

This is quite annoying for me because I use clippy -- --deny warnings in a commit hook.

This also makes it difficult to use with cargo watch (used by for example Rust Analyzer) and wanting to pass --message-format=short or whatever you want in your own build.

[ebroto]

I think this can be closed as it was fixed in clippy#6441