Manual slice fill false positive/suggestion makes it fail

[kayagokalp]

Summary

I recently moved to rust 1.86, and got a false positive/invalid suggestion from clippy about manual slice filling below you can find the reproducer.

I think the report is false positive as I am not actually writing the same value into the slice for each element so I am not filling it but rather applying the same operator to each element so if we are going to be transforming it to something it should be: bytes.iter_mut().for_each(|b| *b = !*b);

Reproducer

for the following piece:

for b in &mut bytes {
    *b = !*b;
}

I got:

warning: manually filling a slice
   --> sway-types/src/u256.rs:140:9
    |
140 | /         for b in &mut bytes {
141 | |             *b = !*b;
142 | |         }
    | |_________^ help: try: `bytes.fill(!*b);`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_slice_fill
    = note: `#[warn(clippy::manual_slice_fill)]` on by default

If this suggestion is applied we get a compile error as b is not a valid variable name anymore.

I expected to see this happen: either no report or suggest bytes.iter_mut().for_each(|b| *b = !*b);

Version

rustc 1.86.0 (05f9846f8 2025-03-31)
binary: rustc
commit-hash: 05f9846f893b09a1be1fc8560e33fc3c815cfecb
commit-date: 2025-03-31
host: aarch64-apple-darwin
release: 1.86.0
LLVM version: 19.1.7

Additional Labels

No response

[profetia]

@rustbot claim

[sminez]

I'm also seeing the manual_slice_fill lint firing incorrectly but in my case it is suggesting calling fill on a custom struct that implements IndexMut rather than a slice (which is obviously completely wrong).

https://github.com/sminez/ad/pull/112/files#diff-b630548d20538fc5ac7df164c7c982cff9665871c95d9aab5d13889d644ab0dbR1044

warning: manually filling a slice
    --> src/ziplist.rs:1047:9
     |
1047 | /         for i in 0..zl.len() {
1048 | |             zl[i] = 6;
1049 | |         }
     | |_________^ help: try: `zl.fill(6);`

[sminez]

Thanks for the fix @profetia !