Unwrap_used false positive with Infallible return value

Summary

Unwrapping a function that returns core::convert::Infallible or std::convert::Infallible results in a false positive clippy::unwrap_used lint.

May be related to #11245

Lint Name

unwrap_used

Reproducer

First I tried this, in a function that returns Result<Svg, Error> where Error is a custom struct based Error type.

let output = Svg::from_str(&svg_string)?;

Which resulted in a error:

error[E0277]: `?` couldn't convert the error to `error::Error`
   --> crates/cdm_core/src/datatypes/project_types/mounting_rail.rs:106:48
    |
106 |         let output = Svg::from_str(&svg_string)?;
    |                      --------------------------^ the trait `std::convert::From<std::convert::Infallible>` is not implemented for `error::Error`
    |                      |
    |                      this can't be annotated with `?` because it has type `Result<_, std::convert::Infallible>`
    |
note: `error::Error` needs to implement `From<std::convert::Infallible>`
   --> crates/cdm_core/src/error.rs:11:1

Fair enough: I tried this to work around the issue:

let output = Svg::from_str(&svg_string).unwrap();

Which triggered the following lints:

// at the call site
clippy::unwrap_used

// on the containing function
clippy::missing_panics_doc

then I tried adding an #[expect]:

#[expect(clippy::unwrap_used, reason = "this function in infalliable")]
let output = Svg::from_str(&svg_string).unwrap();

which triggered the following lints:

// at the call site
clippy::unwrap_used

// on the containing function
clippy::missing_panics_doc

// on the expect attribute
this lint expectation is unfulfilled

I expected to see this happen:

No warning or error while unwrapping the return value of a function that returns core::convert::Infallible or std::convert::Infallible per the fixes in #11245

---

FromStr definition for reference. Infallible is core::convert::Infallible here, but I have also tried std::convert::Infallible with no changes.

impl FromStr for Svg {
    type Err = Infallible;

    //TODO: validation
    /// Creates a `Svg` from a string representation of an Svg. No validation is performed
    /// currently.
    #[inline]
    fn from_str(text: &str) -> Result<Self, Self::Err> {
        Ok(Self {
            svg_data: text.to_owned(),
            filepath: None,
        })
    }
}

Version

rustc 1.94.0 (4a4ef493e 2026-03-02)
binary: rustc
commit-hash: 4a4ef493e3a1488c6e321570238084b38948f6db
commit-date: 2026-03-02
host: x86_64-unknown-linux-gnu
release: 1.94.0
LLVM version: 21.1.8

Additional Labels

No response

Start at the clippy::unwrap_used lint implementation and its existing tests, using the provided Infallible reproducer as the regression case. Confirm that unwrapping a value whose error type is core::convert::Infallible or std::convert::Infallible does not trigger the lint, while ordinary fallible results still do.