Lint negation "followed" by method call

[oli-obk]

Calling -x.foo() will first call foo and then negate. While this is correct as per the precedence rules, it can be surprising (see rust-lang/rust#59388). We should suggest a cleanup either by writing (-x).foo() if that was intended, by writing -(x.foo()) for by introducing an intermediate variable:

let x_foo = x.foo();
-x_foo

[felix91gr]

Yeah, this makes a lot of sense. The precedence rules are perfect for compilers, but people don't necessarily have them ingrained. And code is read much more times than it is written 👍

[Centril]

In my mind -x.foo() is no different than !x.foo(). This is the normal precedence of unary operators which many will understand. So I think this should not be in the complexity category as that would declare -x.foo() to be mostly unidiomatic.

[oli-obk]

I agree. The original issue was on numeric literals, not on variables. On variables it seems pretty clear. Linting -12.foo() but not -x.foo() seems like a middle ground to me.

Note that literals other than integers or floats should not be linted. -"text".some_method() is not negating the string literal and I think that's obvious enough

[memoryruins]

Numeric literals currently emit a precedence lint:

trait Trait { fn method(&self) -> i32 { 42 } }
impl Trait for &str {}

fn main() {
    let a = -42_i32.abs();
    let b = -42_f32.abs();
    let c = -"".method();
    dbg!(a, b, c);
}

warning: unary minus has lower precedence than method call
 --> src/main.rs:5:13
  |
5 |     let a = -42_i32.abs();
  |             ^^^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(42_i32.abs())`
  |
  = note: `#[warn(clippy::precedence)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

warning: unary minus has lower precedence than method call
 --> src/main.rs:6:13
  |
6 |     let b = -42_f32.abs();
  |             ^^^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(42_f32.abs())`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

Is there anything left to do for this issue?