Improve output of E0271 #40186

seanmonstar · 2017-03-01T19:29:58Z

This error is encountered often with futures and tokio, where a returned future has an associated type that doesn't match the expected return type.

An example of current behavior:

error[E0271]: type mismatch resolving `<futures::AndThen<futures::stream::Fold<futures::stream::MapErr<hyper::Body, [closure@src/consumer/pinger.rs:100:41: 107:18 uri:_, request_type:_, correlation_id:_, tx:_, event:_]>, [closure@src/consumer/pinger.rs:107:35: 110:18], futures::FutureResult<std::vec::Vec<u8>, futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>>, std::vec::Vec<u8>>, futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>, [closure@src/consumer/pinger.rs:110:29: 127:18 timer:_, status_code:_, response_status:_, uri:_, tx:_, event:_, headers:_, request_type:_, correlation_id:_]> as futures::IntoFuture>::Error == futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>`
   |
16 |     Box::new(
   |     ^ expected futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>, found struct `io::Error`
   |
   = note: expected type `futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>`
   = note:    found type `io::Error`
   = note: required for the cast to the object type `Future<Error=futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>> + 'static`

And a playpen of a the current behavior (though the error is much smaller): https://is.gd/iigJ2p

A message like this pushes the actionable information down several lines. It may help to instead, output something like this:

error[E0271]: type mismatch resolving `<futures::AndThen<...>::Error`
   |
16 |     Box::new(
   |     ^ expected futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>, found struct `io::Error`
   |
   = note: expected type `futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>`
   = note:    found type `io::Error`
   = note: required for the cast to the object type `Future<Error=futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>> + 'static`
   = note: full type is `<futures::AndThen<futures::stream::Fold<futures::stream::MapErr<hyper::Body, [closure@src/consumer/pinger.rs:100:41: 107:18 uri:_, request_type:_, correlation_id:_, tx:_, event:_]>, [closure@src/consumer/pinger.rs:107:35: 110:18], futures::FutureResult<std::vec::Vec<u8>, futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>>, std::vec::Vec<u8>>, futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>, [closure@src/consumer/pinger.rs:110:29: 127:18 timer:_, status_code:_, response_status:_, uri:_, tx:_, event:_, headers:_, request_type:_, correlation_id:_]> as futures::IntoFuture>::Error == futures::sink::Send<futures::sync::mpsc::Sender<(events::http_request_event::HttpRequestEvent, std::result::Result<consumer::pinger::HttpResult, consumer::pinger::HttpResult>)>>`

Additionally, it might be even clearer to omit some of the type parameters (leaving enough to differentiate) in the 'expected' and 'found' notes, leaving the full type for the bottom note.

error[E0271]: type mismatch resolving `<futures::AndThen<...>::Error`
   |
16 |     Box::new(
   |     ^ expected futures::sink::Send<...>, found struct `io::Error`
   |
   = note: expected type `futures::sink::Send<...>`
   = note:    found type `io::Error`

cc @eddyb

The text was updated successfully, but these errors were encountered:

eddyb · 2017-03-01T21:18:30Z

cc @jonathandturner

estebank · 2017-03-07T21:33:05Z

Related to #21025 (& closed PR #39906).

alexcrichton · 2017-04-10T16:38:57Z

I was searching around for this issue, writing down some keywords so I hopefully can find it easier in the future:

future
too long error message
message too long

@nikomatsakis

…, r=nikomatsakis Highlight and simplify mismatched types Shorten mismatched types errors by replacing subtypes that are not different with `_`, and highlighting only the subtypes that are different. Given a file ```rust struct X<T1, T2> { x: T1, y: T2, } fn foo() -> X<X<String, String>, String> { X { x: X {x: "".to_string(), y: 2}, y: "".to_string()} } fn bar() -> Option<String> { "".to_string() } ``` provide the following output ```rust error[E0308]: mismatched types --> file.rs:6:5 | 6 | X { x: X {x: "".to_string(), y: 2}, y: "".to_string()} | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `std::string::String`, found {integer} | = note: expected type `X<X<_, std::string::String>, _>` ^^^^^^^^^^^^^^^^^^^ // < highlighted found type `X<X<_, {integer}>, _>` ^^^^^^^^^ // < highlighted error[E0308]: mismatched types --> file.rs:6:5 | 10 | "".to_string() | ^^^^^^^^^^^^^^ expected struct `std::option::Option`, found `std::string::String` | = note: expected type `Option<std::string::String>` ^^^^^^^ ^ // < highlighted found type `std::string::String` ``` Fix rust-lang#21025. Re: rust-lang#40186. Follow up to rust-lang#39906. I'm looking to change how this output is accomplished so that it doesn't create list of strings to pass around, but rather add an elided `Ty` placeholder, and use the same string formatting for normal types. I'll be doing that soonish. r? @nikomatsakis

estebank · 2017-09-20T23:22:48Z

Re #43354

estebank · 2019-05-22T01:39:32Z

Current output:

error[E0271]: type mismatch resolving `<std::result::Result<std::result::Result<(), std::result::Result<std::result::Result<(), std::result::Result<std::result::Result<(), std::option::Option<{integer}>>, ()>>, ()>>, ()> as Future>::Error == Foo`
  --> src/main.rs:16:5
   |
16 | /     Box::new(
17 | |         Ok::<_, ()>(
18 | |             Err::<(), _>(
19 | |                 Ok::<_, ()>(
...  |
28 | |         )
29 | |     )
   | |_____^ expected (), found struct `Foo`
   |
   = note: expected type `()`
              found type `Foo`
   = note: required for the cast to the object type `dyn Future<Error = Foo>`

estebank · 2023-01-08T07:52:49Z

Triage: few changes

error[[E0271]](https://doc.rust-lang.org/nightly/error-index.html#E0271): type mismatch resolving `<Result<Result<(), Result<Result<(), Result<Result<(), Option<{integer}>>, ()>>, ()>>, ()> as Future>::Error == Foo`
  --> src/main.rs:16:5
   |
16 | /     Box::new(
17 | |         Ok::<_, ()>(
18 | |             Err::<(), _>(
19 | |                 Ok::<_, ()>(
...  |
28 | |         )
29 | |     )
   | |_____^ type mismatch resolving `<Result<Result<(), Result<Result<(), Result<Result<(), Option<{integer}>>, ()>>, ()>>, ()> as Future>::Error == Foo`
   |
note: expected this to be `Foo`
  --> src/main.rs:6:18
   |
6  |     type Error = E;
   |                  ^
   = note: required for the cast from `Result<Result<(), Result<Result<(), Result<Result<(), Option<{integer}>>, ()>>, ()>>, ()>` to the object type `dyn Future<Error = Foo>`

…-errors Hide more of long types in E0271 Fix rust-lang#40186.

alexcrichton added the A-diagnostics Area: Messages for errors, warnings, and lints label Apr 10, 2017

estebank mentioned this issue Apr 10, 2017

Highlight and simplify mismatched types #41205

Merged

Mark-Simulacrum added the C-enhancement Category: An issue proposing an enhancement or a PR with one. label Jul 26, 2017

estebank mentioned this issue Sep 17, 2017

Refer to types using the local identifier #44642

Closed

estebank mentioned this issue Sep 30, 2017

new-school type mismatch label can be overly long #34905

Closed

estebank added WG-diagnostics Working group: Diagnostics E-needs-mentor labels Nov 29, 2017

crlf0710 added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 11, 2020

estebank mentioned this issue Jan 8, 2023

Hide more of long types in E0271 #106596

Merged

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Jan 12, 2023

Rollup merge of rust-lang#106596 - estebank:verbose-e0271, r=compiler…

890bc3c

…-errors Hide more of long types in E0271 Fix rust-lang#40186.

bors closed this as completed in f1ffe82 Jan 12, 2023

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Improve output of E0271 #40186

Improve output of E0271 #40186

seanmonstar commented Mar 1, 2017

eddyb commented Mar 1, 2017

estebank commented Mar 7, 2017

alexcrichton commented Apr 10, 2017

estebank commented Sep 20, 2017

estebank commented May 22, 2019

estebank commented Jan 8, 2023

Improve output of E0271 #40186

Improve output of E0271 #40186

Comments

seanmonstar commented Mar 1, 2017

eddyb commented Mar 1, 2017

estebank commented Mar 7, 2017

alexcrichton commented Apr 10, 2017

estebank commented Sep 20, 2017

estebank commented May 22, 2019

estebank commented Jan 8, 2023