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Diagnose lifetime/label shadowing during late resolution #95781

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Diagnose lifetime/label shadowing during late resolution #95781

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cjgillot
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@cjgillot cjgillot commented Apr 7, 2022 •
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The current diagnostic is not hygienic. This PR proposes to make it hygienic.
Please advise on the right choice of normalization for it to make sense.

r? @petrochenkov

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Apr 7, 2022
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Some changes occurred in src/tools/rustfmt.

cc @calebcartwright

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 7, 2022
@cjgillot cjgillot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 7, 2022
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@bors try @rust-timer queue

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Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 17, 2022
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bors commented Apr 17, 2022

⌛ Trying commit b8ce429 with merge fe38d6b31dddd83fb3fab1d2f1b764ffeadaffd8...

@petrochenkov petrochenkov added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Apr 17, 2022
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bors commented Apr 17, 2022

☀️ Try build successful - checks-actions
Build commit: fe38d6b31dddd83fb3fab1d2f1b764ffeadaffd8 (fe38d6b31dddd83fb3fab1d2f1b764ffeadaffd8)

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Queued fe38d6b31dddd83fb3fab1d2f1b764ffeadaffd8 with parent 1ec2c13, future comparison URL.

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Finished benchmarking commit (fe38d6b31dddd83fb3fab1d2f1b764ffeadaffd8): comparison url.

Summary:

  • Primary benchmarks: 😿 relevant regression found
  • Secondary benchmarks: mixed results
Regressions 😿
(primary)		 Regressions 😿
(secondary)		 Improvements 🎉
(primary)		 Improvements 🎉
(secondary)		 All 😿 🎉
(primary)
count1 1 1 0 4 1
mean2 2.7% 0.5% N/A -0.9% 2.7%
max 2.7% 0.5% N/A -1.1% 2.7%

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf +perf-regression

Footnotes

  1. number of relevant changes ↩

  2. the arithmetic mean of the percent change ↩

@rustbot rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Apr 17, 2022
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I think we should remove these silly checks entirely.
I mean the function-global conflicts between labels and lifetimes, and labels and other labels, not fn foo<'same, 'bar, 'same>.

They were introduced long time ago in case some new language features appear and require this space.
Now we have another mechanism for such language changes - editions, and if "lifetimes in expressions" or something like that needs to be introduced it could be introduced as an edition change.
However, there was no plans to introduce anything like for years, so it's unlikely that even the edition mechanism will be necessary.

Could you prepare a PR that simply removes these conflicts so we can redirect it to the lang team?

@petrochenkov petrochenkov 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-review Status: Awaiting review from the assignee but also interested parties. labels Apr 21, 2022
@cjgillot cjgillot mentioned this pull request Apr 21, 2022
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@cjgillot cjgillot mentioned this pull request Apr 25, 2022
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Blocked on #96296.

@petrochenkov petrochenkov added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 25, 2022
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 3, 2022
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Auto merge of rust-lang#96296 - cjgillot:remove-label-lt-shadow, r=pe…
3a90bed 
…trochenkov

Remove label/lifetime shadowing warnings

This PR removes some pre-1.0 shadowing warnings for labels and lifetimes.

The current behaviour of the compiler is to warn
* labels that shadow unrelated labels in the same function --> removed
```rust
'a: loop {}
'a: loop {} // STOP WARNING
```

* labels that shadow enclosing labels --> kept, but only if shadowing is hygienic
```rust
'a: loop {
  'a: loop {} // KEEP WARNING
}
```

* labels that shadow lifetime --> removed
```rust
fn foo<'a>() {
  'a: loop {} // STOP WARNING
}
```

* lifetimes that shadow labels --> removed
```rust
'a: loop {
  let b = Box::new(|x: &i8| *x) as Box<dyn for <'a> Fn(&'a i8) -> i8>; // STOP WARNING
}
```

* lifetimes that shadow lifetimes --> kept
```rust
fn foo<'a>() {
  let b = Box::new(|x: &i8| *x) as Box<dyn for <'a> Fn(&'a i8) -> i8>; // KEEP WARNING
}
```

Closes rust-lang#31745.

-----

From `@petrochenkov` in rust-lang#95781 (comment)
> I think we should remove these silly checks entirely.
> They were introduced long time ago in case some new language features appear and require this space.
> Now we have another mechanism for such language changes - editions, and if "lifetimes in expressions" or something like that needs to be introduced it could be introduced as an edition change.
> However, there was no plans to introduce anything like for years, so it's unlikely that even the edition mechanism will be necessary.

r? rust-lang/lang
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Superseded by #96296.

@cjgillot cjgillot deleted the ast-lifetimes-shadow branch June 4, 2022 12:43
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