Suggest using slice when encountering let x = ""[..];

[estebank]

Fix#26319.

[rust-highfive]

r? @eddyb

(rust_highfive has picked a reviewer for you, use r? to override)

[eddyb]

I don't think the index type matters, we should just not check it and just emit the suggestion.

[oli-obk]

You need to add //~ ERROR comments. Ui tests work like compile-fail now

[estebank]

Done.

[oli-obk]

Why just for assignments and not all the cases in the test?

[estebank]

The other cases in the test go through type check instead. I'll see if I can expand #46256 to also suggest in these cases. I included all the cases originally mentioned in order to make sure we don't regress in any of the cases (without noticing).

[estebank]

@eddyb I believe you were right so removed the index type check.

[eddyb]

r? @nikomatsakis I still feel this is much more specific than it should be, but I don't have any good suggestions, other than perhaps that & isn't called "slice-ing" or "taking a slice".
a[..] does the slicing, & just borrows that slice. You can also have a[..].slice_method().

In general, both deref and indexing could use a suggestion to borrow the resulting lvalue.

[arielb1]

this looks dubious. Could you look into this?

[estebank]

Yeah, I noticed that too. Still digging.

[arielb1]

it's also already the case on nightly. Feel free to ignore this and open an issue.

[estebank]

#46302

[arielb1]

This feels hacky to me, but I don't see any better way of implementing this (the rhs of locals is an lvalue, so checks based on it being an rvalue won't quite work).

btw, you should be checking that the problem type is a slice or string - if the return type is a struct or trait object, you don't want the error message to mention "slices".

[arielb1]

OTOH, having an Index implementation that returns trait objects is a bit weird - that would mean someone does some kind of indirection somewhere. But I think "consider borrowing here" would look better than "consider borrowing the slice" (also because str is not a "slice").

[estebank]

@arielb1 reworded.

[arielb1]

@bors r+ rollup

[bors]

📌 Commit fa44927 has been approved by arielb1