erasing_op and identity_op should only be triggered for internal

[Kannen]

Lint name:
- erasing_op
- identity_op

I tried this code:

struct L(i32);
struct Meter;
impl core::ops::Mul<Meter> for  i32 {
    type Output = L;
    fn mul(self,_:Meter) -> L {
        L(self)
    }
}
fn check() {
  let _ = 0 * Meter;  //=> Fire clippy::erasing_op
  let _ = 1 * Meter;  //=> Fire clippy::identity_op
}

Multiply by 0 is not an erasing operation as the type is changed.
Multiply by 1 is not an identity operation as the type is changed.

I suppose that the lint erasing_op may only fire for where 0*x is 0:

let a = AType::new(...);

 let res: i32 = 0 * a; //the result is of the type of the 0
assert!(res;0);  //and the result is 0 <=> this is an erasing_op

And for erasing_op only where 1*x is x (1*x and x should have the same state): e.g:

  let a = AType::new(...);
  let res: AType = 1* a; //the result is of the type of a
  assert_same_binary_representation!(res;a);  //and the result is a

Meta

• cargo clippy -V: clippy 0.1.54 (881c1ac 2021-05-08)
• rustc -Vv:

  rustc 1.54.0-nightly (881c1ac40 2021-05-08)
  binary: rustc
  commit-hash: 881c1ac408d93bb7adaa3a51dabab9266e82eee8
  commit-date: 2021-05-08
  host: x86_64-unknown-linux-gnu
  release: 1.54.0-nightly
  LLVM version: 12.0.0