Clippy falsely reports redundant clone: borrow of moved value

[garritfra]

I tried this code:

fn generate_for_loop(ident: Variable, expr: Expression, body: Statement) -> String {
    // Assign expression to variable to access it from within the loop
    let mut expr_ident = ident.clone();
    expr_ident.name = format!("loop_orig_{}", ident.name);
    let mut out_str = format!("{};\n", generate_declare(&expr_ident, Some(expr)));

    // Loop signature
    out_str += &format!(
        "for (let iter_{I} = 0; iter_{I} < {E}.length; iter_{I}++)",
        I = ident.name,
        E = expr_ident.name
    );

    // Block with prepended declaration of the actual variable
    out_str += &generate_block(
        body,
        Some(format!(
            "let {I} = {E}[iter_{I}];\n",
            I = ident.name,
            E = expr_ident.name,
        )),
    );
    out_str
}

I expected to see this happen: The code to run successfully and apply fixes suggested by cargo clippy --fix.

Instead, this happened: I encountered the following error:

warning: failed to automatically apply fixes suggested by rustc to crate `sb`

after fixes were automatically applied the compiler reported errors within these files:

  * src/generator/js.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see 
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0382]: borrow of moved value: `ident`
   --> src/generator/js.rs:188:47
    |
185 | fn generate_for_loop(ident: Variable, expr: Expression, body: Statement) -> String {
    |                      ----- move occurs because `ident` has type `ast::Variable`, which does not implement the `Copy` trait
186 |     // Assign expression to variable to access it from within the loop
187 |     let mut expr_ident = ident;
    |                          ----- value moved here
188 |     expr_ident.name = format!("loop_orig_{}", ident.name);
    |                                               ^^^^^^^^^^ value borrowed here after move
    |
    = note: this error originates in the macro `$crate::__export::format_args` which comes from the expansion of the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider cloning the value if the performance cost is acceptable
    |
187 |     let mut expr_ident = ident.clone();
    |                               ++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0382`.
Original diagnostics will follow.

warning: redundant clone
   --> src/generator/js.rs:187:31
    |
187 |     let mut expr_ident = ident.clone();
    |                               ^^^^^^^^ help: remove this
    |
note: cloned value is neither consumed nor mutated
   --> src/generator/js.rs:187:

26
    |
187 |     let mut expr_ident = ident.clone();
    |                          ^^^^^^^^^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
    = note: `#[warn(clippy::redundant_clone)]` on by default

warning: `antimony-lang` (bin "sb") generated 1 warning (run `cargo clippy --fix --bin "sb"` to apply 1 suggestion)

Meta

rustc --version --verbose:

rustc 1.72.0-nightly (df77afbca 2023-06-12)
binary: rustc
commit-hash: df77afbcaf3365a32066a8ca4a00ae6fc9a69647
commit-date: 2023-06-12
host: aarch64-apple-darwin
release: 1.72.0-nightly
LLVM version: 16.0.5

(Also present on 1.70.0)

No backtrace is shown.

[garritfra]

Apologies, this is probably the wrong repo. I will reopen the issue in rust-lang/rust-clippy.

EDIT: Issue is rust-lang/rust-clippy#10940