"help: `}` may belong here" no longer reported

[lukas-code]

After #108297, the help message for inserting closing delims is no longer emitted. (cc @chenyukang)

Code

I tried this code:

use std::{mem, ptr;

old output:

error: this file contains an unclosed delimiter
 --> src/main.rs:1:20
  |
1 | use std::{mem, ptr;
  |          -         ^
  |          |
  |          unclosed delimiter

error: expected one of `,`, `::`, `as`, or `}`, found `;`
 --> src/main.rs:1:10
  |
1 | use std::{mem, ptr;
  |          ^        ^
  |          |        |
  |          |        expected one of `,`, `::`, `as`, or `}`
  |          |        help: `}` may belong here
  |          unclosed delimiter

error: expected item, found `}`
 --> src/main.rs:1:20
  |
1 | use std::{mem, ptr;
  |                    ^ expected item

new output

error: this file contains an unclosed delimiter
 --> src/main.rs:1:20
  |
1 | use std::{mem, ptr;
  |          -         ^
  |          |
  |          unclosed delimiter

While noisy, the old output contains a concrete fix (} may belong here) and the new one doesn't.

Version it worked on

It most recently worked on: rustc 1.69.0-nightly (31f858d 2023-02-28)

Version with regression

master at 64165aa, which will be in nightly 2023-03-01

@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged +A-parser +A-diagnostics

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-low

[chenyukang]

Yes, it is a know issue for last PR(we have UI test for it).
It's a tradeoff, I made #108297 based on these considerations:

• unclosed/mismatch delimiter may introduce totally incorrect tokenstream, which will make the parser understand the code totally wrong and give a lot of noisy diagnostics.
• there may be multiple fixes for an unclosed/mismatched delimiter issue, we don't know which one is the best
• the first diagnostics is most important in this scenario.

Given an unclosed delimiter issue, for example, this code:

use std::{mem;

fn main() {
    assert_eq!(4, mem::size_of::<i32>());
}

Stable version will also give the help to add another }:

error: expected one of `,`, `::`, `as`, or `}`, found `;`
 --> src/main.rs:1:10
  |
1 | use std::{mem;
  |          ^   ^
  |          |   |
  |          |   expected one of `,`, `::`, `as`, or `}`
  |          |   help: `}` may belong here
  |          unclosed delimiter

while the better way to fix it is removing the {.

And the output from your description is much more confusing, since user didn't input a }:

error: expected item, found `}`
 --> src/main.rs:1:20
  |
1 | use std::{mem, ptr;
  |                    ^ expected item

[chenyukang]

Another case that mismatch delimiter can not be handled well:

fn bar() -> [u8; 2] {
    foo()
    [1, 3) 
}

fn main() {}

The stable compiler output：

error: expected one of `.`, `?`, `]`, or an operator, found `,`
 --> src/main.rs:4:5
  |
4 |     [1, 3) 
  |     ^ ^ help: `]` may belong here
  |     |
  |     unclosed delimiter

[workingjubilee]

Our diagnostics are unstable. Changes in them are not automatically considered regressions (at least, not without some other detail). As this was an intentional change which yields an improvement in other ways, I am inclined to class this as a non-issue.