needless_match in nightly (2022-03-14) ignores enum arguments

[vakaras]

Summary

When a matched enum has multiple arguments and one of them is replaced, the needless_match lint still reports an error even though the match is not needless.

Lint Name

needless_match

Reproducer

I tried this code:

pub enum E {
    Variant1(u32, bool),
    Variant2(u32, bool),
}

impl E {
    pub fn set_b(self, b: bool) -> Self {
        match self {
            E::Variant1(a, _) => E::Variant1(a, b),
            E::Variant2(a, _) => E::Variant2(a, b),
        }
    }
}

I saw this happen:

> cargo clippy
    Checking needless_match v0.1.0 (/tmp/bla/needless_match)
warning: this match expression is unnecessary
  --> src/lib.rs:9:9
   |
9  | /         match self {
10 | |             E::Variant1(a, _) => E::Variant1(a, b),
11 | |             E::Variant2(a, _) => E::Variant2(a, b),
12 | |         }
   | |_________^ help: replace it with: `self`
   |
   = 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

warning: `needless_match` (lib) generated 1 warning
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s

I expected to see this happen: no warning should be emitted because the new value is constructed with a new b.

Version

rustc 1.61.0-nightly (285fa7ecd 2022-03-14)
binary: rustc
commit-hash: 285fa7ecd05dcbfdaf2faaf20400f5f92b39b3c6
commit-date: 2022-03-14
host: x86_64-unknown-linux-gnu
release: 1.61.0-nightly
LLVM version: 14.0.0

Additional Labels

No response

[lqd]

The lint also now triggers for code like this (playground):

pub fn side_effect() -> Option<String> {
    if let Some(r) = op() {
        Some(r)
    } else {
        println!("side-effect");
        None
    }
}

for an unnecessary if-let expression

warning: this if-let expression is unnecessary
  [--> src/lib.rs:6:5
](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1c35b2a92d8c00e259973cd1f5c1ef38#)   |
6  | /     if let Some(r) = op() {
7  | |         Some(r)
8  | |     } else {
9  | |         println!("side-effect");
10 | |         None
11 | |     }
   | |_____^ help: replace it with: `op()`
   |
   = note: `#[warn(clippy::needless_match)]` on by default

[J-ZhengLi]

@rustbot claim

[teor2345]

The lint also triggers on nightly-2022-03-14 for code like this (playground):

 enum Resultt<T, E> {
     Okk(T),
     Errr(E),
 }
 
 use Resultt::*;
 
 impl<T, E> Resultt<T, E> {
    pub const fn as_ref(self: &Resultt<T, E>) -> Resultt<&T, &E> {
        match self {
            Okk(x) => Okk(x),
            Errr(x) => Errr(x),
        }
    }
}

std::Result does it slightly differently, and doesn't trigger the lint:

    pub const fn as_ref(self: &Result<T, E>) -> Result<&T, &E> {
        match *self {
            Ok(ref x) => Ok(x),
            Err(ref x) => Err(x),
        }
    }

(I've desugared &self, to make it clear what the type change is.)