A `:` instead of a `::` in a path of a `use` item should be a recoverable parsing error

[pnkfelix]

I tried this code:

use std::process:Command;
use std::fs:File;

fn main() { }

I expected to see this happen: I expected to see two diagnostic messages, telling me about the distinct parse errors on lines 1 and 2.

Instead, this happened: The first error was treated as non-recoverable, yielding this output (playground):

error: expected one of `::`, `;`, or `as`, found `:`
 --> src/main.rs:1:17
  |
1 | [use std::process:Command;](https://play.rust-lang.org/#)
  |                 ^ expected one of `::`, `;`, or `as`

error: could not compile `playground` due to previous error

---

I'm assuming recovering in the face of this parse error would be a relatively simple task, given that there is already the : present that should be a strong hint that someone meant to type ::. So I'm tagging this with labels indicating that its a good opportunity for someone who wants to acquaint themselves with the code base.

[pnkfelix]

(This needs a mentor. I am thinking that if someone doesn't pick it up by Friday, then I will see about using it as the basis for one or more instructional videos.)

[compiler-errors]

I can mentor whoever wants to work on this. See https://github.com/rust-lang/rust/blob/master/compiler/rustc_parse/src/parser/item.rs#L950 for the general area where changes need to be made, and ping me if someone needs help on Zulip.

[me-diru]

May I work on this?

[compiler-errors]

You can claim an issue with rustbot, and I recommend checking out the rustc dev guide to find out what the contribution process looks like.

[chetankokil]

@compiler-errors i would like to work on this with your help.

[will-flores1]

@rustbot claim

[will-flores1]

@rustbot release-assignment

[fee1-dead]

This is mostly about adding checks around eat(token::ModSep) such that it recovers when encountering token::Colon. src

However, we would also need the ability to recover to be configurable as arguments to parse_path, as we would want to recover from use std:process::Command as well.

PS: don't take this as is.. I am not that familiar with ast and recovery, but I think this is the main idea