False positive of `same_functions_in_if_condition` with const generics

[fmease]

Summary

When searching for instances of same_functions_in_if_condition, Clippy appears to treat two expressions (namely the conditions inside of if/else chains) as if they were the same even if they differ by const parameter.

In the example given below, Clippy wrongly assumes that foo::<{ T::A }>(x) == 0 and foo::<{ T::B }>(x) == 0 mean the same. Obviously, T::A ≠ T::B but also foo::<{ T::A }>(x) ≠ foo::<{ T::B }>(x) in general.

Lint Name

same_functions_in_if_condition

Reproducer

Of course, the reproducer is but a heavily boiled-down version of real code.

I tried this code (playground):

#![feature(adt_const_params)]
#![allow(incomplete_features)]
#![warn(clippy::same_functions_in_if_condition)]

fn main() {
    let x = 1;     // the program prints "B"
    // let x = -1; // the program prints "A" if this line is uncommented
                   // therefore, the branches are not only
                   // *syntactically* different but also
                   // *semantically* different

    if foo::<{ T::A }>(x) == 0 {
        println!("A");
    } else if foo::<{ T::B }>(x) == 0 {
        println!("B");
    }
}

#[derive(PartialEq, Eq)]
enum T {
    A,
    B,
}

fn foo<const P: T>(x: i32) -> i32 {
    match P {
        T::A => x + 1,
        T::B => x - 1,
    }
}

I saw this happen:

warning: this `if` has the same function call as a previous `if`
  --> src/main.rs:14:15
   |
14 |     } else if foo::<{ T::B }>(x) == 0 {
   |               ^^^^^^^^^^^^^^^^^^^^^^^
   |
note: the lint level is defined here
  --> src/main.rs:3:9
   |
3  | #![warn(clippy::same_functions_in_if_condition)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: same as this
  --> src/main.rs:12:8
   |
12 |     if foo::<{ T::A }>(x) == 0 {
   |        ^^^^^^^^^^^^^^^^^^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#same_functions_in_if_condition

I expected to see this happen:

No warning being printed to stderr.

Version

rustc 1.59.0-nightly (48a5999fc 2021-12-01)
binary: rustc
commit-hash: 48a5999fceeea84a8971634355287faa349909d4
commit-date: 2021-12-01
host: x86_64-unknown-linux-gnu
release: 1.59.0-nightly
LLVM version: 13.0.0

Additional Labels

@rustbot label +T-const-generics