MIR borrowck: error message confuses locals and temporaries #46598

davidtwco · 2017-12-09T11:47:28Z

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

davidtwco · 2017-12-09T11:48:26Z

~~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 · 2017-12-10T17:56:27Z

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 · 2017-12-10T18:02:31Z

src/librustc_mir/borrow_check/mod.rs

-        err.emit();
+        match &self.describe_place(place) {
+            Some(description) => {
+                let mut err = self.tcx.path_does_not_live_long_enough(


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

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

This should now be being handled.

arielb1 · 2017-12-10T18:08:53Z

Nice!

@bors r+ p=1

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

bors · 2017-12-10T18:08:54Z

📌 Commit e1723d2 has been approved by arielb1

arielb1 · 2017-12-10T18:10:02Z

@bors p=0

This hasn't passed travis yet

kennytm · 2017-12-10T18:53:31Z

@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 · 2017-12-10T21:20:04Z

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 · 2017-12-11T17:30:08Z

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

arielb1 · 2017-12-11T18:46:01Z

src/librustc_mir/borrow_check/mod.rs

+            // See test ui/issue-46471.rs for this case.
+            RegionKind::ReEarlyBound(_) | RegionKind::ReFree(_) => proper_span,
+            // See test compile-fail/issue-36082.rs for this case.
+            _ if name == "borrowed value" => span,


nit: use if !with_name

arielb1 · 2017-12-11T18:56:13Z

src/librustc_mir/borrow_check/mod.rs

+        };
+
+        let mut err = self.tcx.path_does_not_live_long_enough(err_span, &name, Origin::Mir);
+        match borrow.region {


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 · 2017-12-11T19:06:52Z

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 · 2017-12-11T19:07:56Z

@kennytm

We're working on it.

bors · 2017-12-11T19:22:47Z

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

davidtwco · 2017-12-11T20:55:37Z

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

arielb1 · 2017-12-11T21:00:12Z

src/librustc_mir/borrow_check/error_reporting.rs

+            },
+            // This case should not happen.
+            RegionKind::ReLateBound(_, _) | RegionKind::ReSkolemized(_, _) |
+                RegionKind::ReErased => {


nit: indentation

davidtwco · 2017-12-11T22:21:00Z

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 · 2017-12-12T03:41:32Z

That's cool!

@bors r+

bors · 2017-12-12T03:41:33Z

📌 Commit 3dbc11b has been approved by arielb1

bors · 2017-12-12T06:11:38Z

⌛ Testing commit 3dbc11b with merge 7245006...

@arielb1

MIR borrowck: error message confuses locals and temporaries Fixes #46471 and fixes #46472 (see [this Gitter comment](https://gitter.im/rust-impl-period/WG-compiler-nll?at=5a2d5cb53ae2aa6b3facf0c2)). r? @arielb1

bors · 2017-12-12T08:45:23Z

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

rust-highfive assigned arielb1 Dec 9, 2017

kennytm added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 9, 2017

davidtwco changed the title ~~WIP: MIR borrowck: error message confuses locals and temporaries~~ MIR borrowck: error message confuses locals and temporaries Dec 10, 2017

arielb1 reviewed Dec 10, 2017

View reviewed changes

arielb1 reviewed Dec 11, 2017

View reviewed changes

davidtwco added 5 commits December 11, 2017 19:46

Added test for #46471

4651d1e

Fix error message confuses locals and temporaries

d78e8a7

Added test for #46472

15b8fbd

Fix error does not know about free/named lifetimes

52442d4

Fixed case where borrowed value lives until after scope

baf68d3

arielb1 reviewed Dec 11, 2017

View reviewed changes

davidtwco added 2 commits December 11, 2017 22:20

Refactored and tidied up report function

00c7a3f

Updated existing tests with new error messages.

3dbc11b

bors merged commit 3dbc11b into rust-lang:master Dec 12, 2017

davidtwco deleted the issue-46471 branch December 20, 2017 16:05

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MIR borrowck: error message confuses locals and temporaries #46598

MIR borrowck: error message confuses locals and temporaries #46598

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MIR borrowck: error message confuses locals and temporaries #46598

MIR borrowck: error message confuses locals and temporaries #46598

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