manual_inspect suggestion breaks mutating code #13185
Description
Summary
Here is a playground link: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=e4fad507e221cf2e8540575031233165
The suggestion leads to broken code which does not compile:
error[E0594]: cannot assign to `a.a`, which is behind a `&` reference
--> src/main.rs:18:9
|
17 | let ref_mut_opt = opt.as_mut().inspect(|a| {
| - consider changing this binding's type to be: `&mut &mut A`
18 | a.a += 123;
| ^^^^^^^^^^ `a` is a `&` reference, so the data it refers to cannot be written
Using inspect, I end up with & &mut A, and I can’t seem to be able to mutate things through that reference.
Changing the signature as suggested in the second compiler error is also not possible.
Lint Name
manual_inspect
Reproducer
I tried this code:
#[derive(Debug)]
struct A {
a: u32,
}
fn main() {
// warns but works:
let mut opt = Some(A { a: 123 });
let ref_mut_opt = opt.as_mut().map(|a| {
a.a += 123;
a
});
dbg!(ref_mut_opt);
}I saw this happen:
warning: using `map` over `inspect`
--> src/main.rs:9:36
|
9 | let ref_mut_opt = opt.as_mut().map(|a| {
| ^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect
= note: `#[warn(clippy::manual_inspect)]` on by default
help: try
|
9 ~ let ref_mut_opt = opt.as_mut().inspect(|a| {
10~ a.a += 123;
|
Version
rustc 1.82.0-nightly (7120fdac7 2024-07-25)
binary: rustc
commit-hash: 7120fdac7a6e55a5e4b606256042890b36067052
commit-date: 2024-07-25
host: x86_64-apple-darwin
release: 1.82.0-nightly
LLVM version: 18.1.7
Additional Labels
No response