clippy::if_then_panic warning (nightly)

[Bromeon]

This is not a pressing issue yet, but it appears in a nightly version of clippy, so you might be interested in addressing the lint ahead of time.

I'm using this simple snippet:

use approx::assert_relative_eq;

fn main() {
    assert_relative_eq!(1.0, 2.0);
}

When running cargo +nightly clippy, I get:

warning: only a `panic!` in `if`-then statement
 --> src\main.rs:4:2
  |
4 |     assert_relative_eq!(1.0, 2.0);
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(clippy::if_then_panic)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_then_panic
  = note: this warning originates in the macro `__assert_approx` (in Nightly builds, run with -Z macro-backtrace for more info)

This occurred in the CI of the downstream project godot-rust, which treats clippy warnings as errors (the nightly workflow still passes though).

---

It has to do with how the __assert_approx macro is implemented.
Basically, the lint tries to detect the structure

if !cond { panic!(msg); }

and transform it into

assert!(cond, msg);

This would be one option to fix it, another would be to #[allow(clippy::if_then_panic)] the relevant statements.

I'm using rustc 1.57.0-nightly (5b210643e 2021-10-11).

[EFanZh]

I think #72 has fixed this issue, so maybe this can be closed?

[Bromeon]

The Clippy lint has been renamed and moved categories in the meantime: rust-lang/rust-clippy#7810

However, it still seems to occur with approx v0.5.0.
A crate with only this code:

fn main() {
    approx::assert_relative_eq!(1.0, 1.0);
}

results in:

cargo clippy -- -D clippy::pedantic
    Checking ctest v0.1.0 (<path/to/project>)
error: only a `panic!` in `if`-then statement
 --> src\main.rs:2:5
  |
2 |     approx::assert_relative_eq!(1.0, 1.0);
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `-D clippy::manual-assert` implied by `-D clippy::pedantic`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_assert
  = note: this error originates in the macro `__assert_approx` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `<crate>` due to previous error

[EFanZh]

The fix was just merged a few days ago, new version containing the fix hasn’t been released yet.