I tried this code:

#[warn(x)]
fn main() {}

I expected to see this happen: Clippy warns once that x is an unknown lint.

Instead, this happened: Clippy warns twice.

warning: unknown lint: `x`
 --> src/main.rs:1:8
  |
1 | #[warn(x)]
  |        ^
  |
  = note: `#[warn(unknown_lints)]` on by default

warning: unknown lint: `x`
 --> src/main.rs:1:8
  |
1 | #[warn(x)]
  |        ^

warning: 2 warnings emitted

Meta

• cargo clippy -V: 0.1.51 (2021-01-16 8a65184)
• rustc -V: 1.49.0

See also rust-lang/rust#80524 (comment) - this looks unrelated to the UNKNOWN_CLIPPY_LINTS pass because it shows up even with that disabled.

cc @flip1995