needless_match doesn't consider the else of if let

[goffrie]

Summary

The needless_match lint produces a nonsensical suggestion in some cases. It seems like it fires entirely based on the if-clause of an if let, ignoring the else branch's value entirely. This is a regression, most likely from #8549 (but I haven't confirmed that).

Lint Name

needless_match

Reproducer

I tried this code:

pub fn bad() -> Option<i32> {
    if let Some(existing) = None {
        Some(existing)
    } else {
        Some(123)
    }
}

I saw this happen:

warning: this if-let expression is unnecessary
 [--> src/lib.rs:2:5
](https://play.rust-lang.org/#)  |
2 | /     if let Some(existing) = None {
3 | |         Some(existing)
4 | |     } else {
5 | |         Some(123)
6 | |     }
  | |_____^ help: replace it with: `None`
  |
  = note: `#[warn(clippy::needless_match)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_match

I expected to see no lint error.

Version

rustc 1.62.0-nightly (1f7fb6413 2022-04-10)
binary: rustc
commit-hash: 1f7fb6413d6d6c0c929b223e478e44c3db991b03
commit-date: 2022-04-10
host: x86_64-unknown-linux-gnu
release: 1.62.0-nightly
LLVM version: 14.0.0

Additional Labels

No response

[J-ZhengLi]

@rustbot claim

[fanninpm]

Does #8700 fix this?

[goffrie]

Does #8700 fix this?

Yes, I think it does.