Compiler error due to web::block opaque type

[sylvain101010]

Hi,
the following code causes a compiler error:

fn handle_upload(report_path: &str, field: Field) -> Box<Stream<Item = (), Error = Error>> {
    let file = match fs::File::create(report_path) {
        Ok(file) => file,
        Err(e) => return Box::new(future::err(error::ErrorInternalServerError(e)).into_stream()),
    };

    return Box::new(
        Box::new(
            field.fold((file, 0u64), move |(mut file, mut acc), bytes| {
                web::block(move || {
                    file.write_all(bytes.as_ref()).map_err(|e| {
                        MultipartError::Payload(error::PayloadError::Io(e))
                    })?;
                    acc += bytes.len() as u64;
                    if acc > crate::REPORT_MAX_SIZE {
                        return Err(MultipartError::Payload(error::PayloadError::Overflow));
                    }
                    Ok((file, acc))
                })
                .map_err(|e: error::BlockingError<MultipartError>| {
                    match e {
                        error::BlockingError::Error(e) => e,
                        error::BlockingError::Canceled => MultipartError::Incomplete,
                    }
                })
            })
            .map(|(_)| ())
            .map_err(|e| error::ErrorInternalServerError(e)),
        ).into_stream()
    );
}

cause the following error:

error: internal compiler error: unexpected region in query response: `ReScope(Destruction(282))`

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:354:17
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::_print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
   6: std::panicking::begin_panic
   7: <rustc_errors::Handler as core::ops::drop::Drop>::drop
   8: core::ptr::real_drop_in_place
   9: core::ptr::real_drop_in_place
  10: core::ptr::real_drop_in_place  11: syntax::with_globals
  12: __rust_maybe_catch_panic
  13: <F as alloc::boxed::FnBox<A>>::call_box
  14: std::sys::unix::thread::Thread::new::thread_start
  15: _pthread_body
  16: _pthread_start
query stack during panic:
end of query stack

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.34.1 

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `api`.

as you can see, the code is not very different than https://github.com/actix/examples/tree/master/multipart

according to rust-lang/rust#60127

The reason may be the opaque return type of web::block.

Is it possible to improve this ?

[fafhrd91]

You should file rustc bug report

[sylvain101010]

I just tested with nightly and it compiles without error, so effectively a rustc error.

Sorry for the inconveniences