When encountering move error on an Option, suggest using as_ref

[estebank]

Fix #61109, cc #15457.

[rust-highfive]

r? @eddyb

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

[estebank]

r? @oli-obk

[czipperz]

Does this correctly handle as_mut as well?

[czipperz]

Perhaps this should support Result as well?

[estebank]

@czipperz adding Result support now.

Does this correctly handle as_mut as well?

Could you expand?

[czipperz]

I don't know if this is possible, but it would be nice if it suggested as_mut when you need mutable access to call a method. as_ref().unwrap() converts Option<T> to &T but sometimes you need &mut T.

[oli-obk]

How do you feel about waiting a bit with merging this PR (a bit being until #60966 is merged)? Then you can annotate Option and Result with #[rustc_diagnostic_item = "option"] and "result" respectively and then check for these items via

if let Some(adt) = original_path.ty(self.mir, self.infcx.tcx).adt_def() {
	if self.infcx.tcx.is_diagnostic_item(adt.did, sym::option) {
        ...
    }
}

[estebank]

There are a couple of places where we're already doing string comparisons like this, so I love the fact that we'll be able to get rid of them soon!

[oli-obk]

Hmm... or we can just merge this and fix it up later, doesn't seem like a big deal in fact.

[estebank]

I'm fine either way

[estebank]

@czipperz suggesting both is bit heavy, but can be done. I'm a bit ambivalent on whether it is worth it. On one hand, it teaches the API surface nicely, on the other hand it is verbose and might confuse newcomers.

[oli-obk]

My vote is for just suggesting as_ref and figuring out how to make sure we emit good errors on subsequent errors that may occur due to the code actually requiring mutable references

[estebank]

Should I just remove the last commit or are there any further changes needed (beyond #60966)?

[oli-obk]

r=me with last commit removed. I agree with your assessment that we'd be overwhelming users for little gain

[estebank]

@bors r=oli-obk

[bors]

📌 Commit 1cc42ea has been approved by oli-obk

[bors]

⌛ Testing commit 1cc42ea with merge ed2a511...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: oli-obk
Pushing ed2a511 to master...

[nnethercote]

https://twitter.com/nnethercote/status/1083507450249043969