`question_mark` lint triggers wrongly for `if let` in closure that does not return a `Result`

[sdroege]

Summary

See details below

Lint Name

question_mark

Reproducer

I tried this code:

    src_pad.add_probe(gst::PadProbeType::BUFFER, |_, probe_info| {
        if let Some(gst::PadProbeData::Buffer(ref buffer)) = probe_info.data {
            let map = buffer.map_readable().unwrap();

            let samples = if let Ok(samples) = map.as_slice_of::<i16>() {
                samples
            } else {
                return gst::PadProbeReturn::Ok;
            };
            [...]
        }

        gst::PadProbeReturn::Ok
    });

I saw this happen:

warning: this if-let-else may be rewritten with the `?` operator
  --> examples/src/bin/pad_probes.rs:54:27
   |
54 |               let samples = if let Ok(samples) = map.as_slice_of::<i16>() {
   |  ___________________________^
55 | |                 samples
56 | |             } else {
57 | |                 return gst::PadProbeReturn::Ok;
58 | |             };
   | |_____________^ help: replace it with: `map.as_slice_of::<i16>()?`
   |
   = note: `#[warn(clippy::question_mark)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#question_mark

I expected to see this happen: Nothing because the closure does not return a Result

Version

rustc 1.58.0 (02072b482 2022-01-11)
binary: rustc
commit-hash: 02072b482a8b5357f7fb5e5637444ae30e423c40
commit-date: 2022-01-11
host: x86_64-unknown-linux-gnu
release: 1.58.0
LLVM version: 13.0.0

Additional Labels

@rustbot label +I-suggestion-causes-error

[Alexendoo]

This is fixed on nightly, would be by #7860 or #8080

[sdroege]

Indeed, with nightly this doesn't happen anymore. Thanks!