manual_memcpy suggest slicing array when not necessary

[sosthene-nitrokey]

Summary

The manual_memcpy can suggest slicing an array with [..N] even if the type of the array is [T; N], which makes the slicing unnecessary.

Reproducer

I tried this code:

    let src: &[u8] = todo!();
    let mut dest = [0; 4];
    
    for i in 0..4 {
        dest[i] = src[i];
    }

Clippy suggests dest[..4].copy_from_slice(&src[..4]);, but the dest[..4] is unnecessary as dest as a compile-time known length of 4.

The same happens when reversing the roles with:

    let dest: &mut [u8] = todo!();
    let src = [0; 4];
    
    for i in 0..4 {
        dest[i] = src[i];
    }

The suggestion is the same but now the src[..4] slicing is unnecessary.

Version

rustc 1.73.0 (cc66ad468 2023-10-03)
binary: rustc
commit-hash: cc66ad468955717ab92600c770da8c1601a4ff33
commit-date: 2023-10-03
host: x86_64-unknown-linux-gnu
release: 1.73.0
LLVM version: 17.0.2

Additional Labels

No response

[granddaifuku]

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