error[E0275]: "overflow evaluating the requirement" triggered by importing a path of length 2

[zhaofengli]

This might be a duplicate of #39959. I'm posting a new issue here as the mechanism that the error is triggered significantly differs from that in the aforementioned issue.

Sample code

[package]
name = "example"
version = "0.1.0"
authors = ["Author"]
edition = "2018"

[dependencies]
tokio = "=0.1.14"

use std::fs::File;
use std::io::{Read, Write};
use std::path::Path;

// Comment this out... and everything will work fine
use thisdoesntexistyolo::haha;

struct Something<T: Read + Write> {
    thing: T,
}

impl<'a, T: 'a + Read + Write> Something<T>
where
    &'a T: Read,
{
    fn new(thing: T) -> Something<T> {
        Something { thing }
    }
}

fn main() {
    let file = File::open(Path::new("doesntmatter.txt")).unwrap();
    let mut st: Something<File> = Something::new(file);
}

(Playground)

error[E0432]: unresolved import `thisdoesntexistyolo`
 --> src/main.rs:6:5
  |
6 | use thisdoesntexistyolo::haha;
  |     ^^^^^^^^^^^^^^^^^^^ use of undeclared type or module `thisdoesntexistyolo`

warning: unused import: `thisdoesntexistyolo::haha`
 --> src/main.rs:6:5
  |
6 | use thisdoesntexistyolo::haha;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unused_imports)] on by default

error[E0275]: overflow evaluating the requirement `_: std::marker::Sized`
  --> src/main.rs:23:35
   |
23 |     let mut st: Something<File> = Something::new(file);
   |                                   ^^^^^^^^^^^^^^
   |
   = help: consider adding a `#![recursion_limit="128"]` attribute to your crate
   = note: required because of the requirements on the impl of `std::io::Read` for `&tokio_reactor::poll_evented::PollEvented<_>`
   = note: required because of the requirements on the impl of `std::io::Read` for `&tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<_>>`
   = note: required because of the requirements on the impl of `std::io::Read` for `&tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<_>>>`
   = note: required because of the requirements on the impl of `std::io::Read` for `&tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<_>>>>`
[...]
   = note: required because of the requirements on the impl of `std::io::Read` for `&tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<tokio_reactor::poll_evented::PollEvented<_>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`

Details

• This issue will still occur if the imported package is real.
• When use thisdoesntexistyolo::haha; is replaced with anything more than 2 levels deep like use thisdoesntexistyolo::a::b;, the code will compile without the error.

[csmoe]

cc @shepmaster it seems a playground issue, cannot reproduce on a local machine.

[zhaofengli]

I can reproduce it locally with Arch Linux's rustc:

rustc 1.32.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-linux-gnu
release: 1.32.0
LLVM version: 7.0

I wouldn't have used Playground if I weren't having issue on a local machine. However, I did some testing with other versions, and here are some interesting results:

• 👎 arch rustc 1.32.0 reproduced
• 👎 playground rustc 1.32.0 reproduced
• 👍 rustup rustc 1.32.0 (9fda7c223 2019-01-16) cannot reproduce
• 👍 rustup rustc 1.24.0 (4d90ac38c 2018-02-12) cannot reproduce
• 👍 rustup rustc 1.33.0-nightly (4c2be9c97 2019-01-22) cannot reproduce

Looking at Arch Linux's build script for Rust, it appears to be a normal build with a custom config.toml.

[shepmaster]

cannot reproduce on a local machine.

Have you added both the tokio and tar crates (based on the error messages)?

[shepmaster]

Yes, adding just Tokio triggers this. I've updated the original comment.

[shepmaster]

/cc @davidtwco does this feel like anything around the external crate trait suggestions you worked on?

[davidtwco]

/cc @davidtwco does this feel like anything around the external crate trait suggestions you worked on?

I don't think so - the extern crate trait suggestions work (#55613) I've done hasn't landed (I feel like there was something like that I had done which landed, but I can't find it, so I suppose not).

[shepmaster]

hasn't landed

Oh, heh, then pretty unlikely to be related 😊! Sorry to drag you in!

[zhaofengli]

Looks like the bug definitely depends on a certain package (tokio) being pulled in, but does not necessarily require a non-existent import. In my original code, importing actix-web (use actix_web::{server, Query, State, App};) was what triggered this bug.

[shepmaster]

but does not necessarily require a non-existent import

Oh, you said that in your original comment; sorry.