"error[E0435]: attempt to use a non-constant value in a constant" shows wrong fix with mut variables

[yedayak]

I tried this code:

fn main() {
    let mut length: usize = 2;
    let arr = [0; length];
}

I expected to see this happen: Get an error about using non constant values in a constant, with a help pointer showing where to change "let" to "const", like in this example without the mut keyword:

2 |     let length: usize = 2;
  |     ---------- help: consider using `const` instead of `let`: `const length`

Instead, this happened: I get the correct error, but it points to a wrong place to fix, off by one character:

2 |     let mut length: usize = 2;
  |      ------------- help: consider using `const` instead of `let`: `const length`

This means auto correcting it using the rust-analyzer vscode plugin produces invalid code:

lconst length: usize = 2;

Meta

rustc --version --verbose:

rustc 1.59.0-nightly (efec54529 2021-12-04)
binary: rustc
commit-hash: efec545293b9263be9edfb283a7aa66350b3acbf
commit-date: 2021-12-04
host: x86_64-pc-windows-msvc
release: 1.59.0-nightly
LLVM version: 13.0.0

[FabianWolff]

The same problem occurs when there is additional whitespace:

fn main() {
    let   length: usize = 2;
    let arr = [0; length];
}

error[E0435]: attempt to use a non-constant value in a constant
 --> t2.rs:3:19
  |
2 |     let   length: usize = 2;
  |       ---------- help: consider using `const` instead of `let`: `const length`
3 |     let arr = [0; length];
  |                   ^^^^^^ non-constant value

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