Suggest &str.chars() on attempt to &str.iter()

[TaKO8Ki]

closes #90786

[rust-highfive]

r? @jackh726

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[wooster0]

Here's a similar error:

error[E0277]: `&str` is not an iterator
   --> src/main.rs:2:14
    |
2   |     for x in "hello" {}
    |              ^^^^^^^ `&str` is not an iterator; try calling `.chars()` or `.bytes()`
    |
    = help: the trait `Iterator` is not implemented for `&str`
    = note: required because of the requirements on the impl of `IntoIterator` for `&str`
note: required by `into_iter`

Maybe this one should mention bytes too?

[estebank]

I would prefer it if we could have a more... generalized solution for this problem. One that I've seen presented is an #[alias("alt_name")] attribute, where we could manually annotate methods in std with common names used in other languages for the same behavior. In this case we could annotate #[alias("iter", "codepoints")] fn chars and let that machinery do the rest.

But in the meantime I'm not against landing targeted solutions, although it is additional tech debt.

[estebank]

@r00ster91 that error occurs in a separate part of the compiler. E0599 occurs during typeck, while E0277 occurs during trait resolution. It is also using the #[rustc_on_unimplemented], which is why it doesn't have a structured suggestion, just a label.

[jackh726]

r? @estebank

[estebank]

There's some trailing whitespace, but after fixing that r=me

[estebank]

@bors r+

[bors]

📌 Commit d562f48 has been approved by estebank