clippy::match_ref_pats probably shouldn't fire for if let

[CAD97]

Lint name:

I tried this code:

if let &KeyboardInput {
    keycode: Some(keycode),
    state,
    ..
} = event
{
    // ...
}

I expected to see this happen: warning free

Instead, this happened: clippy::match_ref_pats matched

The point of clippy::match_ref_pats is that it's less notation to put a single deref on the matched value than a ref on every pattern, but with if let this doesn't apply, as there's only one pattern to begin with.

Either the description/help message should change when only one pattern is present, or clippy::match_ref_pats should only be emitted when more than one pattern are present.

Meta

Rust version (rustc -Vv):

rustc 1.56.0-nightly (ad02dc46b 2021-08-26)
binary: rustc
commit-hash: ad02dc46badee510bd3a2c093edf80fcaade91b1
commit-date: 2021-08-26
host: x86_64-pc-windows-msvc
release: 1.56.0-nightly
LLVM version: 13.0.0

[camsteffen]

For that matter, we should probably not lint match if there is just one &.

[1nF0rmed]

So, would we be suggesting that for a single &, the clippy::match_ref_pats should be suppressed?

If so, are there any tests around this and what's the part of the code that I should be looking at for this?

[camsteffen]

Hi @1nF0rmed. Yes that's correct. You can find the implementation here and tests here. You can comment with @rustbot claim to self-assign this issue.

[1nF0rmed]

Thank you for the pointers!
Just wanted to confirm my approach. Given we are passing the patterns here, should we add a check in the implementation

rust-clippy/clippy_lints/src/matches.rs

Line 1185 in 78e7312

fn check_match_ref_pats<'a, 'b, I>(cx: &LateContext<'_>, ex: &Expr<'_>, pats: I, expr: &Expr<'_>)

where we iterate through the patterns and count the number of occurrences of PatKind::Ref(..).
If the count, in that case, is 1, then we just return

[camsteffen]

It looks like you could just modify has_only_ref_pats (and rename to has_multiple_ref_pats).

[1nF0rmed]

Hey, thank you so much for the pointers. are we able to add this to hacktoberfest?

[camsteffen]

I think any PR will count?

[1nF0rmed]

Can I pick up this issue? @camsteffen

[camsteffen]

Yes just comment with @rustbot claim

[1nF0rmed]

@rustbot claim