Targeted suggestions for specific "no method" errors on standard library types

[dtolnay]

Rustc currently shows a perfectly reasonable error message when calling a nonexistent method:

use std::collections::BTreeSet;

fn main() {
    let mut set = BTreeSet::new();
    set.push("");
}

error[E0599]: no method named `push` found for type `std::collections::BTreeSet<_>` in the current scope
 --> src/main.rs:5:9
  |
5 |     set.push("");
  |         ^^^^

But for specific frequently encountered cases, it would be great to show a more targeted error that gives the name of the method you almost definitely meant to call, despite not being similar enough to trigger the "did you mean" suggestion.

Candidates would be cases that arise often from refactoring (this applies to BTreeSet::push, which I see every now and then after replacing a Vec with a BTreeSet) or cases of a Rust API being named differently from an equivalent C++ API.

• BTreeSet::push ⟶ suggest insert
• Vec::push_back ⟶ suggest push
• VecDeque::push ⟶ suggest push_back
• Vec::length, Vec::size ⟶ suggest len

[estebank]

Do you think this would be a common enough pattern that it'd be worth creating something like rustc_on_unimplemented but for confusables?

Something like

trait BTreeSet {
    #[rustc_confusables("insert")]
    fn push() {}
}

error[E0599]: no method named `push` found for type `std::collections::BTreeSet<_>` in the current scope
 --> src/main.rs:5:9
  |
5 |     set.push("");
  |         ^^^^ help: you might have meant to use `insert`

[dtolnay]

Something similar to rustc_on_unimplemented sounds like it would work! I don't know enough about the diagnostics implementation to know what the other options are.

Bonus points if it is straightforward for a new rustc contributor to add a confusable and corresponding test case.

[fmease]

We could also reuse (abuse?) #[doc(alias = "…")] for this. I think I've seen this mentioned a few times.

[kadiwa4]

Maybe relevant: #107108 adds doc(alias) support to that error

[jieyouxu]

Now that PR #112239 is merged, it should be easy to add #[rustc_confusables(...)] to some of these methods along with some tests.