Give recursion limit errors a span

[oli-obk]

For example in https://github.com/rust-lang/rust/blob/master/tests/ui/infinite/infinite-struct.rs we get an error like

error: reached the recursion limit finding the struct tail for `Take`
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]`

We could pass in the obligation cause to struct_tail_raw and use its span for the main message and report a note for the obligation

Originally posted by @oli-obk in #135464 (comment)

[tanvincible]

Hello @oli-obk! I'd like to take a stab at it.

@rustbot claim

[tanvincible]

Hello @oli-obk! Could you please provide some instructions on how I should proceed to tackle this issue?

[oli-obk]

My plan would be to look at all calls to struct_tail_raw and check if there's an ObligationCause (or an Obligation containing one) nearby and pass that in. For the sites that have none, I'd just pass in an ObligationCause::misc() with a span that's nearby. Then I'd (in two separate commits), first use the span of the obligation to make the error point to that span instead of a DUMMY_SP, and second, check where other code annotates a Diag with an ObligationCause and call that code. The second step requires creating an error instead of emitting it (different method on the same dcx) and then mutating the Diag before emitting it. As the second step is more involved and I'd need to do research myself to figure it out, you can either dig into it, or just land the main span improvement first.

[tanvincible]

Thanks! I'd try to land the main span improvement first.

[oli-obk]

In that case you could even avoid passing an obligation and just pass a span (which you sometimes get from an obligation) to struct_tail_raw

[JumpiiX]

Hello @tanvincible , I noticed this issue has been assigned to you for some time, and I’d love to contribute. Are you still actively working on it, or would you mind if I take over? Let me know. Thanks!

[tanvincible]

Hello @JumpiiX! I am sorry, I got busy and forgot to release the issue assignment. Feel free to take over the issue.

@rustbot release-assignment

[JumpiiX]

@rustbot claim