Suggested spelling correction seems off-base

[dtolnay]

In https://www.reddit.com/r/rust/comments/gpw2ra/how_is_the_rust_compiler_able_to_tell_the_visible/ I noticed this surprising spelling suggestion:

#![feature(non_ascii_idents)]

fn main() {
    let _ = 读文;
}

error[E0425]: cannot find value `读文` in this scope
   --> src/main.rs:45:13
    |
45  |     let _ = 读文;
    |             ^^^^ help: a tuple variant with a similar name exists: `Ok`

To me 读文 and Ok don't seem like they would be similar enough to meet the threshold for showing such a suggestion. Can we calibrate this better for short idents?

For comparison, even kO doesn't assume you mean Ok.

error[E0425]: cannot find value `kO` in this scope
  --> src/main.rs:45:13
   |
45 |     let _ = kO;
   |             ^^ not found in this scope

rustc 1.45.0-nightly (8970e8b 2020-05-23)

Mentioning @estebank who worked on suggestions most recently in #65421.

[Enselic]

I debugged it a bit. Ok is selected as the candidate because the edit distance is just 2 to 读文.

The code to fix is likely in or around fn find_best_match_for_name_impl. I tried some quick tricks but got ICEs and failing tests and gave up. One thing I didn't try that could perhaps work is to consider edit distance between characters of different alphabets/logogram sets as infinite, rather than 1, which is the case right now.

[dtolnay]

Thank you for investigating!

Independent of what we do with different logogram sets (your suggestion sounds plausible), an edit distance of 2 for a string of length 2 should not meet the threshold for showing a suggestion, even within a single logogram set.

[Enselic]

I think edit distance of 1 for a string of length 1 is reasonable (a lot of existing UI tests relies on it), but maybe an edit distance of 2 for a string of length 2 is not reasonable indeed.

As you point out, with regular chars, the edit distance is still 2 but Ok is not suggested. So maybe there is a simpler fix to be made for 读文 than looking at what alphabets/logogram sets characters belong to.