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Use an 'approximate' universal upper bound when reporting region errors #73806

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merged 1 commit into from
Jul 1, 2020
Merged

Use an 'approximate' universal upper bound when reporting region errors #73806

merged 1 commit into from
Jul 1, 2020

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Aaron1011
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Fixes #67765

When reporting errors during MIR region inference, we sometimes use
universal_upper_bound to obtain a named universal region that we
can display to the user. However, this is not always possible - in a
case like fn foo<'a, 'b>() { .. }, the only upper bound for a region
containing 'a and 'b is 'static. When displaying diagnostics, it's
usually better to display some named region (even if there are
multiple involved) rather than fall back to a generic error involving
'static.

This commit adds a new approx_universal_upper_bound method, which
uses the lowest-numbered universal region if the only alternative is to
return 'static.

@Aaron1011
Use an 'approximate' universal upper bound when reporting region errors
517d361 
Fixes rust-lang#67765

When reporting errors during MIR region inference, we sometimes use
`universal_upper_bound` to obtain a named universal region that we
can display to the user. However, this is not always possible - in a
case like `fn foo<'a, 'b>() { .. }`, the only upper bound for a region
containing `'a` and `'b` is `'static`. When displaying diagnostics, it's
usually better to display *some* named region (even if there are
multiple involved) rather than fall back to a generic error involving
`'static`.

This commit adds a new `approx_universal_upper_bound` method, which
uses the lowest-numbered universal region if the only alternative is to
return `'static`.
@rust-highfive
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r? @estebank

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

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 27, 2020
@Aaron1011 Aaron1011 mentioned this pull request Jun 27, 2020
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estebank
estebank approved these changes Jun 27, 2020
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The code changes look reasonable and the output improvements are very welcome. I left a couple of nitpicks, but r=me.

src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.stderr
Comment on lines +14 to +17
help: to force the closure to take ownership of `a` (and any other referenced variables), use the `move` keyword
|
LL | [0].iter().flat_map(|a| [0].iter().map(move |_| &a));
| ^^^^^^^^
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Can we make this one // run-rustfix now?

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The suggestion doesn't actually fix it - it just gets the error message back to the original one.

src/librustc_mir/borrow_check/region_infer/mod.rs
/// Therefore, this method should only be used in diagnostic code,
/// where displaying *some* named universal region is better than
/// falling back to 'static.
pub(in crate::borrow_check) fn approx_universal_upper_bound(&self, r: RegionVid) -> RegionVid {
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Could we move this to somewhere in src/librustc_mir/borrow_check/diagnostics/ and make it accessible only there?

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This method can't easily be moved, since it references private fields in RegionInferenceContext.

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@bors r+

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bors commented Jun 29, 2020

📌 Commit 517d361 has been approved by estebank

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 29, 2020
Manishearth added a commit to Manishearth/rust that referenced this pull request Jun 29, 2020
@Manishearth
Rollup merge of rust-lang#73806 - Aaron1011:feature/approx-universal-…
2fef102 
…upper, r=estebank

Use an 'approximate' universal upper bound when reporting region errors

Fixes rust-lang#67765

When reporting errors during MIR region inference, we sometimes use
`universal_upper_bound` to obtain a named universal region that we
can display to the user. However, this is not always possible - in a
case like `fn foo<'a, 'b>() { .. }`, the only upper bound for a region
containing `'a` and `'b` is `'static`. When displaying diagnostics, it's
usually better to display *some* named region (even if there are
multiple involved) rather than fall back to a generic error involving
`'static`.

This commit adds a new `approx_universal_upper_bound` method, which
uses the lowest-numbered universal region if the only alternative is to
return `'static`.
@Manishearth Manishearth mentioned this pull request Jun 29, 2020
Closed
Manishearth added a commit to Manishearth/rust that referenced this pull request Jun 29, 2020
@Manishearth
Rollup merge of rust-lang#73806 - Aaron1011:feature/approx-universal-…
00ccc67 
…upper, r=estebank

Use an 'approximate' universal upper bound when reporting region errors

Fixes rust-lang#67765

When reporting errors during MIR region inference, we sometimes use
`universal_upper_bound` to obtain a named universal region that we
can display to the user. However, this is not always possible - in a
case like `fn foo<'a, 'b>() { .. }`, the only upper bound for a region
containing `'a` and `'b` is `'static`. When displaying diagnostics, it's
usually better to display *some* named region (even if there are
multiple involved) rather than fall back to a generic error involving
`'static`.

This commit adds a new `approx_universal_upper_bound` method, which
uses the lowest-numbered universal region if the only alternative is to
return `'static`.
@Manishearth Manishearth mentioned this pull request Jun 29, 2020
Closed
Manishearth added a commit to Manishearth/rust that referenced this pull request Jun 30, 2020
@Manishearth
Rollup merge of rust-lang#73806 - Aaron1011:feature/approx-universal-…
0e585c3 
…upper, r=estebank

Use an 'approximate' universal upper bound when reporting region errors

Fixes rust-lang#67765

When reporting errors during MIR region inference, we sometimes use
`universal_upper_bound` to obtain a named universal region that we
can display to the user. However, this is not always possible - in a
case like `fn foo<'a, 'b>() { .. }`, the only upper bound for a region
containing `'a` and `'b` is `'static`. When displaying diagnostics, it's
usually better to display *some* named region (even if there are
multiple involved) rather than fall back to a generic error involving
`'static`.

This commit adds a new `approx_universal_upper_bound` method, which
uses the lowest-numbered universal region if the only alternative is to
return `'static`.
@Manishearth Manishearth mentioned this pull request Jun 30, 2020
Closed
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Is there a chance this PR is massively slowing down CI? It was a part of two rollups (#73880, #73864) that timed out, and while this is not the only suspect, it's worth investigating.

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@bors r- try @rust-timer queue

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Awaiting bors try build completion

@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jun 30, 2020
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bors commented Jun 30, 2020

⌛ Trying commit 517d361 with merge 91c610e689edb8d299333c89cc783cf7b3727b61...

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bors commented Jun 30, 2020

☀️ Try build successful - checks-actions, checks-azure
Build commit: 91c610e689edb8d299333c89cc783cf7b3727b61 (91c610e689edb8d299333c89cc783cf7b3727b61)

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Queued 91c610e689edb8d299333c89cc783cf7b3727b61 with parent 665190b, future comparison URL.

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Finished benchmarking try commit (91c610e689edb8d299333c89cc783cf7b3727b61): comparison url.

@Aaron1011
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No perf impact

@bors r=estebank

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bors commented Jun 30, 2020

📌 Commit 517d361 has been approved by estebank

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 30, 2020
@Manishearth Manishearth mentioned this pull request Jul 1, 2020
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Jul 1, 2020
@bors
Auto merge of rust-lang#73924 - Manishearth:rollup-8r51ld9, r=Manishe…
f781bab 
…arth

Rollup of 17 pull requests

Successful merges:

 - rust-lang#72071 (Added detailed error code explanation for issue E0687 in Rust compiler.)
 - rust-lang#72369 (Bring net/parser.rs up to modern up to date with modern rust patterns)
 - rust-lang#72445 (Stabilize `#[track_caller]`.)
 - rust-lang#73466 (impl From<char> for String)
 - rust-lang#73548 (remove rustdoc warnings)
 - rust-lang#73649 (Fix sentence structure)
 - rust-lang#73678 (Update Box::from_raw example to generalize better)
 - rust-lang#73705 (stop taking references in Relate)
 - rust-lang#73716 (Document the static keyword)
 - rust-lang#73752 (Remap Windows ERROR_INVALID_PARAMETER to ErrorKind::InvalidInput from Other)
 - rust-lang#73776 (Move terminator to new module)
 - rust-lang#73778 (Make `likely` and `unlikely` const, gated by feature `const_unlikely`)
 - rust-lang#73805 (Document the type keyword)
 - rust-lang#73806 (Use an 'approximate' universal upper bound when reporting region errors)
 - rust-lang#73828 (Fix wording for anonymous parameter name help)
 - rust-lang#73846 (Fix comma in debug_assert! docs)
 - rust-lang#73847 (Edit cursor.prev() method docs in lexer)

Failed merges:

r? @ghost
@bors bors merged commit f213957 into rust-lang:master Jul 1, 2020
@SNCPlay42 SNCPlay42 mentioned this pull request Aug 21, 2020
Closed
@cuviper cuviper added this to the 1.46 milestone May 2, 2024
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Unhelpful error messages from borrow checker with async/await
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@Aaron1011 @rust-highfive @estebank @bors @Manishearth @Mark-Simulacrum @rust-timer @cuviper