manual_unwrap_or_default false positive with a nested pattern

[magicant]

Summary

The manual_unwrap_or_default lint seems to incorrectly suggest replacing a pattern match with an unwrap_or_default call if the branch returning the non-default value has a nested pattern like Some(Some(x)) or Some(MyEnum::MyVariant(x)).

Lint Name

manual_unwrap_or_default

Reproducer

I tried this code:

fn main() {
    let v = match Some(Some(42)) {
        Some(Some(x)) => x,
        _ => Default::default(),
    };
    println!("{v}");
}

I saw this happen:

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

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

  * src/main.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[E0277]: `std::option::Option<{integer}>` doesn't implement `std::fmt::Display`
 --> src/main.rs:3:15
  |
3 |     println!("{v}");
  |               ^^^ `std::option::Option<{integer}>` cannot be formatted with the default formatter
  |
  = help: the trait `std::fmt::Display` is not implemented for `std::option::Option<{integer}>`
  = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
  = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
Original diagnostics will follow.

warning: match can be simplified with `.unwrap_or_default()`
 --> src/main.rs:2:13
  |
2 |       let v = match Some(Some(42)) {
  |  _____________^
3 | |         Some(Some(x)) => x,
4 | |         _ => Default::default(),
5 | |     };
  | |_____^ help: replace it with: `Some(Some(42)).unwrap_or_default()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_unwrap_or_default
  = note: `#[warn(clippy::manual_unwrap_or_default)]` on by default

warning: `clippy-tmp` (bin "clippy-tmp" test) generated 1 warning (run `cargo clippy --fix --bin "clippy-tmp" --tests` to apply 1 suggestion)

I expected to see this happen:

No suggestions should be produced.

Version

rustc 1.79.0 (129f3b996 2024-06-10) (Fedora 1.79.0-3.fc40)
binary: rustc
commit-hash: 129f3b9964af4d4a709d1383930ade12dfe7c081
commit-date: 2024-06-10
host: x86_64-unknown-linux-gnu
release: 1.79.0
LLVM version: 18.1.6

Additional Labels

@rustbot label +I-suggestion-causes-error

[y21]

This bug was fixed in #12961 (duplicate of #12928). Thanks for reporting this regardless!

[magicant]

Great, thank you for the quick attention!