`expect_fun_call` gives untypable suggestion

[samueltardieu]

Summary

Some suggestions made by the expect_fun_call lint fail to type.

Reproducer

I tried this code:

#[deny(clippy::expect_fun_call)]
fn f(x: Option<i32>) {
    let s = String::from("foo");
    let s = s.as_ref();
    _ = x.expect(std::convert::identity(s));
    println!("s = {s}");
}

I expected to see this happen: an actionable suggestion

Instead, this happened:

7 |     _ = x.expect(std::convert::identity(s));
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_else(|| { panic!("{}", std::convert::identity(s).to_string()) })`

When applied, the suggestion doesn't compile:

error[E0282]: type annotations needed for `&_`
 --> t.rs:6:9
  |
6 |     let s = s.as_ref();
  |         ^
7 |     _ = x.unwrap_or_else(|| { panic!("{}", std::convert::identity(s).to_string()) });
  |                                                                      --------- type must be known at this point

Version

rustc 1.90.0-nightly (f26e58023 2025-06-30)
binary: rustc
commit-hash: f26e58023071e71636a3c72ac3a2bf89b1f76706
commit-date: 2025-06-30
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.7

Additional Labels

@rustbot label +I-suggestion-causes-error