-A --allow should take precedence over -D --deny in CLI

[tyranron]

I have a weird issue, where I cannot disable a single lint via command line.

Running the following

cargo +beta clippy --all -- -D clippy::pedantic -D warnings \
	                    -A clippy::must_use_candidate

still results in lint being applied:

error: this method could have a `#[must_use]` attribute
  --> crates/tracerr/src/trace.rs:50:5
   |
50 |     fn deref(&self) -> &Vec<Frame> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: add the attribute: `#[must_use] fn deref(&self) -> &Vec<Frame>`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#must_use_candidate

Changing the order of the CLI arguments doesn't affect anything.

While disabling lint via !#[allow(clippy::must_use_candidate)] attribute in crate's root works OK, as expected.

I suggest that things listed in allow (no matter where) as a white list should take precedence over deny as a black list.

❯ cargo +beta clippy -- --version
clippy 0.0.212 (c8e3cfbd 2019-10-28)

[flip1995]

The logic of handling command line lint flags is in rustc, not in Clippy:
https://github.com/rust-lang/rust/blob/61a551b4939ec1d5596e585351038b8fbd0124ba/src/librustc/lint/levels.rs#L68-L75

To check if this is a Clippy issue: What is the result of rustc -D unused -A dead_code main.rs?

---

Answer:

$ rustc -Dunused -Adead_code src/main.rs
error: function is never used: `foo`
 --> src/main.rs:5:1
  |
5 | fn foo() {}
  | ^^^^^^^^
  |
  = note: `-D dead-code` implied by `-D unused`

error: aborting due to previous error

So yeah this has to be addressed in rustc, not in Clippy. I keep this issue open, because, this behavior would also be nice to have from the Clippy perspective.