Refactor the macro code about ruma HOT 14 CLOSED

fn try_from(...) -> Result<T, OuterError> {
    let try_from_impl = move || {
        fallible_operation_1()?;
        fallible_operation_2()?;
        fallible_operation_3()
    };

    try_from_impl().map_err(|e| OuterError {
        msg: e,
        context: ...,
    })
}

Ok(Self {
    room_id: {
        let segment = path_segments.get(4usize).unwrap().as_bytes();
        let try_from_impl =
            move || -> Result<_, ruma_api::error::DeserializationError> {
                let decoded =
                    ruma_api::exports::percent_encoding::percent_decode(segment)
                        .decode_utf8()
                        .map_err(ruma_api::error::DeserializationError::from)?;

                std::convert::TryFrom::try_from(decoded.deref()).map_err(Into::into)
            };
        match try_from_impl() {
            Ok(val) => val,
            Err(err) => {
                return Err(RequestDeserializationError::new(err, request).into())
            }
        }
    },
    event_id: {
        let segment = path_segments.get(6usize).unwrap().as_bytes();
        let try_from_impl =
            move || -> Result<_, ruma_api::error::DeserializationError> {
                let decoded =
                    ruma_api::exports::percent_encoding::percent_decode(segment)
                        .decode_utf8()
                        // Into::into needs type anotations here
                        .map_err(ruma_api::error::DeserializationError::from)?;

                std::convert::TryFrom::try_from(decoded.deref()).map_err(Into::into)
            };
        // this is the only field that can use `.map_err` in this example since it's the last
        try_from_impl().map_err(|err| RequestDeserializationError::new(err, request))?
    },
})

let try_from_impl = move |segment| -> Result<_, ruma_api::error::DeserializationError> {
    let decoded = ruma_api::exports::percent_encoding::percent_decode(segment)
        .decode_utf8()
        .map_err(ruma_api::error::DeserializationError::from)?;

    std::convert::TryFrom::try_from(decoded.deref()).map_err(Into::into)
};

Ok(Self {
    room_id: {
        let segment = path_segments.get(4usize).unwrap().as_bytes();
        match try_from_impl(segment) {
            Ok(val) => val,
            Err(err) => {
                return Err(RequestDeserializationError::new(err, request).into())
            }
        }
    },
    event_id: {
        let segment = path_segments.get(6usize).unwrap().as_bytes();
        try_from_impl(segment)
            .map_err(|err| RequestDeserializationError::new(err, request))?
    },
})

#extract_request_path
#extract_request_query
#extract_request_headers
#extract_request_body

Ok(Self {
    #parse_request_path
    #parse_request_query
    #parse_request_headers
    #parse_request_body
})