`match_as_ref` suggestion is not equivalent to the matching code

[mmtftr]

Summary

let dbtx_ref = match db_tx {
    Some(ref mut db_tx) => Some(db_tx),
    None => dbtx.as_deref_mut(),
};

The suggestion says let dbtx_ref = db_tx.as_mut(); which is not accurate. It should've been let dbtx_ref = db_tx.as_mut().or_else(|| /* whatever's in the None branch if not None */)

Lint Name

match_as_ref

Reproducer

I tried this code:

<code>
let dbtx_ref = match db_tx {
    Some(ref mut db_tx) => Some(db_tx),
    None => dbtx.as_deref_mut(),
};
</code>

I saw this happen:

<output>
let dbtx_ref = db_tx.as_mut();
</output>

I expected to see this happen:

<output>
let dbtx_ref = db_tx.as_mut().or(dbtx.as_deref_mut());
</output>

Version

rustc 1.85.1 (4eb161250 2025-03-15)
binary: rustc
commit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181
commit-date: 2025-03-15
host: aarch64-apple-darwin
release: 1.85.1
LLVM version: 19.1.7

Additional Labels

No response

[samueltardieu]

Compilable reproducer, confirmed reproducible in master as of 2025-09-17:

use std::ops::{Deref, DerefMut};

struct A(B);
struct B;

impl Deref for A {
    type Target = B;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for A {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

fn main() {
    let mut a = Some(A(B));
    let mut b = Some(B);
    let _ = match b {
        Some(ref mut x) => Some(x),
        None => a.as_deref_mut(),
    };
}

@rustbot label +I-suggestion-causes-bug