MIR borrowck: error message confuses locals and temporaries

[davidtwco]

Fixes #46471 and fixes #46472 (see this Gitter comment).

r? @arielb1

[davidtwco]

This isn't quite there yet, the error output is approximately correct, but the spans are a character to the left of what they should be to match exactly. I think this was a issue with tabs locally, not seeing it anymore so consider this resolved.

I'm also not sure that the condition I'm checking is what I should be using for this, but it works.

static lifetime is also hardcoded at the moment, I've seen the note_and_explain_region function and tried to use that but I struggled to find a ScopeTree to pass to it (flow_state.borrows.base_results.operator().scope_tree was closest I could find but was private).

I think it might also be worth splitting the report_borrowed_value_does_not_live_long_enough function into two smaller functions and moving the condition to the callers, it seems to be doing two different things. Interested to hear thoughts on this.

[davidtwco]

I've fixed issues referenced in my previous comment and also fixed #46472 as mentioned in this Gitter comment.

I think the function might be getting a bit a unwieldly since it's handling a bunch of cases. I've adjusted tests to allow the handful of places where spans are off by a character.

[arielb1]

This doesn't handle the case where a local needs to live until an end_span, aka

let x = {
    let y = 0;
    &y
};

[davidtwco]

This should now be being handled.

[arielb1]

Nice!

@bors r+ p=1

This should go before #46558, which changes the same code.

[bors]

📌 Commit e1723d2 has been approved by arielb1

[arielb1]

@bors p=0

This hasn't passed travis yet

[kennytm]

@bors r-

Travis failed.

[00:57:14] failures:
[00:57:14]     [ui] ui/nll/capture-ref-in-struct.rs
[00:57:14]     [ui] ui/nll/closure-requirements/escape-argument.rs
[00:57:14]     [ui] ui/nll/closure-requirements/escape-upvar-nested.rs
[00:57:14]     [ui] ui/nll/closure-requirements/escape-upvar-ref.rs

[davidtwco]

I've fixed the previous issue where a local might need to live until an end_span. I've not looked at the other tests which are failing in the Travis build - do these just need updated to have the improved error messages or is this an issue with this PR @arielb1?

[davidtwco]

I've updated the existing tests to use the new error messages. This should now pass Travis.

[arielb1]

nit: use if !with_name

[arielb1]

There looks to be quite some connection between the span and the error message, so I would prefer to have 4 separate functions - 1 for each distinct error messagee

[kennytm]

Travis is still failing.

[00:59:30] ---- [compile-fail] compile-fail/borrowck/borrowck-local-borrow-outlives-fn.rs stdout ----
[00:59:30] 	
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/borrowck/borrowck-local-borrow-outlives-fn.rs:15: unexpected error: '15:5: 15:7: `x` does not live long enough [E0597]'
[00:59:30] 
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/borrowck/borrowck-local-borrow-outlives-fn.rs:16: expected error not found: borrowed value does not live long enough
[00:59:30] 
[00:59:30] error in revision `mir`: 1 unexpected errors found, 1 expected errors not found
...
[00:59:30] ---- [compile-fail] compile-fail/borrowck/borrowck-local-borrow-with-panic-outlives-fn.rs stdout ----
[00:59:30] 	
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/borrowck/borrowck-local-borrow-with-panic-outlives-fn.rs:16: unexpected error: '16:15: 16:23: `z.1` does not live long enough [E0597]'
[00:59:30] 
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/borrowck/borrowck-local-borrow-with-panic-outlives-fn.rs:18: expected error not found: [E0597]
[00:59:30] 
[00:59:30] error in revision `mir`: 1 unexpected errors found, 1 expected errors not found
...
[00:59:30] ---- [compile-fail] compile-fail/region-borrow-params-issue-29793-big.rs stdout ----
[00:59:30] 	
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/region-borrow-params-issue-29793-big.rs:84: unexpected error: '84:5: 84:6: `x` does not live long enough [E0597]'
[00:59:30] 
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/region-borrow-params-issue-29793-big.rs:84: unexpected error: '84:5: 84:6: `y` does not live long enough [E0597]'
[00:59:30] 
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/region-borrow-params-issue-29793-big.rs:84: expected error not found: borrowed value does not live long enough
[00:59:30] 
[00:59:30] error in revision `mir`: /checkout/src/test/compile-fail/region-borrow-params-issue-29793-big.rs:84: expected error not found: borrowed value does not live long enough
[00:59:30] 
[00:59:30] error in revision `mir`: 2 unexpected errors found, 2 expected errors not found

If nothing goes wrong, #46558 will be merged soon, so you'll likely need to rebase.

[arielb1]

@kennytm

We're working on it.

[bors]

☔ The latest upstream changes (presumably #46558) made this pull request unmergeable. Please resolve the merge conflicts.

[davidtwco]

All previous issues should be resolved and it's now rebased on top of the current master (or as of an hour ago).

[arielb1]

nit: indentation

[davidtwco]

Alright, fifth time lucky. I've fixed the indentation and other requested changes from Gitter and updated the failing tests from the recent Travis run.

[arielb1]

That's cool!

@bors r+

[bors]

📌 Commit 3dbc11b has been approved by arielb1

[bors]

⌛ Testing commit 3dbc11b with merge 7245006...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: arielb1
Pushing 7245006 to master...