Cargo clippy report warnings from macros when using quote_spanned

Summary

Cargo clippy captures warnings from inside macros when using quote_spanned!. Attempting --fix results in: warning: failed to automatically apply fixes suggested by rustc to crate ..... after fixes were automatically applied the compiler reported errors within these files ....

Replacing quote_spanned with quote here made the bug disappear.

Reproducer

The code does not fit in a snippet, unfortunately multiple crates are required But a small reproducer may be found here

I expected to see no warnings when running cargo clippy.

Instead, this happened:

warning: this let-binding has unit value
  --> marshalable/src/lib.rs:15:5
   |
15 |     _b: (),
   |     ^^ help: omit the `let` binding: `_b;`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_unit_value
   = note: `#[warn(clippy::let_unit_value)]` on by default
warning: `marshalable` (lib) generated 1 warning (run `cargo clippy --fix --lib -p marshalable` to apply 1 suggestion)

Futhermore attempting ``--fix` causes clippy error:

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

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

  * marshalable/src/lib.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

But this might be a side effect.

Version

rustc 1.80.1 (3f5fd8dd4 2024-08-06)
binary: rustc
commit-hash: 3f5fd8dd41153bc5fdca9427e9e05be2c767ba23
commit-date: 2024-08-06
host: x86_64-unknown-linux-gnu
release: 1.80.1
LLVM version: 18.1.7

Additional Labels

No response

Start with the reproducer linked in the issue, especially marshalable-derive/src/lib.rs at the quote_spanned! call and marshalable/src/lib.rs where the warning appears. Run cargo clippy and cargo clippy --fix on the reproducer, then compare behavior with quote; done means the macro-generated warning and failed fix are resolved without introducing compiler errors.