Compiler suggests writing &mut mut foo in E0277 with .as_slice() #105645
Description
Given the following code:
fn main() { let mut buf = [0u8; 50]; let mut bref = buf.as_slice(); foo(&mut bref); } fn foo(_: &mut impl std::io::Write) {}The current output is:
error[E0277]: the trait bound `&[u8]: std::io::Write` is not satisfied --> src/main.rs:4:9 | 4 | foo(&mut bref); | --- ^^^^^^^^^ the trait `std::io::Write` is not implemented for `&[u8]` | | | required by a bound introduced by this call | = help: the trait `std::io::Write` is implemented for `&mut [u8]` note: required by a bound in `foo` --> src/main.rs:7:21 | 7 | fn foo(_: &mut impl std::io::Write) {} | ^^^^^^^^^^^^^^ required by this bound in `foo` help: consider changing this borrow's mutability | 4 | foo(&mut mut bref); | ~~~~ Notice that the suggestion is to write foo(&mut mut bref), which is both invalid syntax and not where the problem is located — as_slice() returns an & reference, so that call must be changed and no local syntax change can work.
Occurs on stable 1.65.0 and 1.68.0-nightly (2022-12-11 bdb07a8)