`clippy::useless_format` slices `{name}` to `am.to_string()`

[CAD97]

Summary

Fun with off-by-ones.

cc @compiler-errors didn't you just fix something similar to this in rustc or am I imagining things

Reproducer

I tried this code:

fn main() {
    let variable = "string";
    let _ = format!("{variable}");

    let abc = "abc";
    let _ = format!("{abc}");

    let x = "x";
    let _ = format!("{x}");

    let xx = "xx";
    let _ = format!("{xx}");
}

I expected to see this happen:

warning: useless use of `format!`
 --> src\main.rs:3:13
  |
3 |     let _ = format!("{variable}");
  |             ^^^^^^^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `variable.to_string()`
  |
  = note: `#[warn(clippy::useless_format)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

warning: useless use of `format!`
 --> src\main.rs:6:13
  |
6 |     let _ = format!("{abc}");
  |             ^^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `abc.to_string()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

warning: useless use of `format!`
 --> src\main.rs:9:13
  |
9 |     let _ = format!("{x}");
  |             ^^^^^^^^^^^^^^ help: consider using `.to_string()`: `x.to_string()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

warning: useless use of `format!`
  --> src\main.rs:9:13
   |
12 |     let _ = format!("{xx}");
   |             ^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `xx.to_string()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

Instead, this happened:

warning: useless use of `format!`
 --> src\main.rs:3:13
  |
3 |     let _ = format!("{variable}");
  |             ^^^^^^^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `ariabl.to_string()`
  |
  = note: `#[warn(clippy::useless_format)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

warning: useless use of `format!`
 --> src\main.rs:6:13
  |
6 |     let _ = format!("{abc}");
  |             ^^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `b.to_string()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

warning: useless use of `format!`
 --> src\main.rs:9:13
  |
9 |     let _ = format!("{x}");
  |             ^^^^^^^^^^^^^^ help: consider using `.to_string()`: `x.to_string()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

warning: useless use of `format!`
  --> src\main.rs:9:13
   |
12 |     let _ = format!("{xx}");
   |             ^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `.to_string()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

Note the suggestions: they've mangled the name of the bindings by slicing off the first and last character.

Version

rustc 1.64.0-nightly (f8588549c 2022-07-18)
binary: rustc
commit-hash: f8588549c3c3d45c32b404210cada01e2a45def3
commit-date: 2022-07-18
host: x86_64-pc-windows-msvc
release: 1.64.0-nightly
LLVM version: 14.0.6

Additional Labels

@rustbot label +I-suggestion-causes-error