Stabilise feature(never_type). Introduce feature(exhaustive_patterns) #47630

canndrew · 2018-01-21T08:52:03Z

This stabilizes !, removing the feature gate as well as the old defaulting-to-() behavior. The pattern exhaustiveness checks which were covered by feature(never_type) have been moved behind a new feature(exhaustive_patterns) gate.

rust-highfive · 2018-01-21T08:52:07Z

r? @estebank

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bors · 2018-01-21T09:19:19Z

☔ The latest upstream changes (presumably #47622) made this pull request unmergeable. Please resolve the merge conflicts.

varkor · 2018-01-21T09:33:09Z

src/libcore/cmp.rs

@@ -880,24 +880,24 @@ mod impls {

    ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }

-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.24.0")]


Shouldn't this be since = "1.25.0"?

True, it's too late to make 1.24. Thanks for the catch!

nagisa · 2018-01-21T14:35:03Z

r? @nikomatsakis

dtolnay

I believe when we split a feature gate into stable part and unstable part, we typically try to rename the stable part rather than the unstable part. So in this case ! would be stabilized under something like feature(never_bang) and what you have as feature(exhaustive_patterns) would continue to be feature(never_type). This minimizes churn for libraries that currently use never_type. Their existing code would continue to compile.

nikomatsakis · 2018-01-23T17:04:02Z

If I understand correctly, this will also resolve the future compatibiltiy question (and make the change to fallback to ! instead of ()). Therefore, It seems like we should do a crater run to test the impact.

@bors try

nikomatsakis · 2018-01-23T17:04:02Z

If I understand correctly, this will also resolve the future compatibility question in #39216 (and make the change to fallback to ! instead of ()). Therefore, It seems like we should do a crater run to test the impact.

@bors try

bors · 2018-01-23T17:04:13Z

⌛ Trying commit 72ce701 with merge e2e6c4a...

Stabilise feature(never_type). Introduce feature(exhaustive_patterns) This stabilizes `!`, removing the feature gate as well as the old defaulting-to-`()` behavior. The pattern exhaustiveness checks which were covered by `feature(never_type)` have been moved behind a new `feature(exhaustive_patterns)` gate.

bors · 2018-01-23T19:43:06Z

☀️ Test successful - status-travis
State: approved= try=True

SimonSapin · 2018-01-24T08:42:39Z

The pattern exhaustiveness checks which were covered by feature(never_type) have been moved behind a new feature(exhaustive_patterns) gate.

I haven’t followed all the discussions around !, could you give some examples of code affected by this? In this different from what’s already possible on stable with empty enums?

SimonSapin · 2018-01-24T08:48:35Z

Never mind, I saw your explenation on #35121 (comment). As to empty enums, this also causes error[E0005]: refutable pattern in local binding: `Err(_)` not covered

    enum Void {}
    let r: Result<u32, Void> = Ok(4);
    let Ok(i) = r;

canndrew · 2018-01-24T15:11:45Z

@dtolnay That would mean only the pattern-matching stuff is behind the never_type feature gate though, which would make it a bit of a misnomer.

As it is I deleted the never_type feature entirely. When I tried to add it back in order to follow https://forge.rust-lang.org/stabilization-guide.html it caused errors from anything tagged with stable(feature = "never_type", since = "1.25.0") complaining about mismatching issue numbers. There are no other stable tags with issue numbers so I don't know what it wants exactly.

nikomatsakis · 2018-01-24T20:06:55Z

@canndrew huh, I've never seen those particular errors before

aidanhs · 2018-01-25T22:23:00Z

Crater run started.

aidanhs · 2018-01-31T01:20:06Z

Crater run is currently stalled due to runs taking up more disk space than they used to. We've started up a bigger box and are working through the backlog - ETA another week or so, sorry :(

canndrew · 2018-02-01T05:05:43Z

@nikomatsakis

huh, I've never seen those particular errors before

Specifically, I added (accepted, never_type, "1.25.0", Some(35121)) to the list of accepted features in features.rs. I then get tidy errors saying mismatches to corresponding lang feature in: ["tracking issue"] for all lines that say #[stable(feature = "never_type", since = "1.25.0")]

aidanhs · 2018-02-08T17:57:06Z

When this is ready for another run can you get bors to do a try? Then we'll prioritise this PR since it's been idle and waiting for a while.

nikomatsakis · 2018-03-14T19:15:11Z

@bors r+

@canndrew 🎸 👏 🎸

bors · 2018-03-14T19:15:12Z

📌 Commit a8a0c69 has been approved by nikomatsakis

bors · 2018-03-14T23:43:10Z

⌛ Testing commit a8a0c69 with merge 5ebf748...

Stabilise feature(never_type). Introduce feature(exhaustive_patterns) This stabilizes `!`, removing the feature gate as well as the old defaulting-to-`()` behavior. The pattern exhaustiveness checks which were covered by `feature(never_type)` have been moved behind a new `feature(exhaustive_patterns)` gate.

bors · 2018-03-15T02:16:51Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 5ebf748 to master...

canndrew · 2018-03-15T04:39:03Z

@clarcharr I've submitted a PR for replacing Infallible with !: #49038

…kennytm re-mark the never docs as unstable Fixes rust-lang#54198 This stability attribute was removed in rust-lang#47630, but not replaced with a `#[stable]` attribute, and when rust-lang#50121 reverted that stabilization, it didn't set the docs back to unstable. I'm concerned as to why it was allowed to not have the stability attribute at all, but at least this can put it back. I'm nominating this for beta backport because it's a really small change, and right now our docs are in an awkward position where the `!` type is technically unstable to use, but the docs don't say so the same way any other library feature would. (And this is also the case *on stable* now, but i'm not suggesting a stable backport for a docs fix.)

rust-highfive assigned estebank Jan 21, 2018

canndrew mentioned this pull request Jan 21, 2018

Tracking issue for promoting ! to a type (RFC 1216) #35121

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varkor reviewed Jan 21, 2018

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canndrew force-pushed the exhaustive-patterns branch from cc3e60c to 72ce701 Compare January 21, 2018 10:30

rust-highfive assigned nikomatsakis and unassigned estebank Jan 21, 2018

matthewjasper mentioned this pull request Jan 21, 2018

add docs for never type rust-lang/reference#206

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kennytm added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 21, 2018

dtolnay reviewed Jan 21, 2018

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kennytm added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 23, 2018

scottmcm mentioned this pull request Jan 24, 2018

Tracking issue for TryFrom/TryInto traits #33417

Closed

3 tasks

canndrew force-pushed the exhaustive-patterns branch from 72ce701 to 71fa69c Compare February 1, 2018 08:11

nikomatsakis force-pushed the exhaustive-patterns branch from 71fa69c to c3beef6 Compare February 8, 2018 19:15

fix ui test error again

a8a0c69

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 Mar 14, 2018

kennytm added the relnotes Marks issues that should be documented in the release notes of the next release. label Mar 15, 2018

bors merged commit a8a0c69 into rust-lang:master Mar 15, 2018

davll mentioned this pull request Mar 22, 2018

Replace Never with ! rust-lang/futures-rs#897

Closed

messense mentioned this pull request Mar 23, 2018

Compile with stable Rust rwf2/Rocket#19

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11 tasks

scottmcm mentioned this pull request Mar 31, 2018

It would be nice if searching for ! in the docs gave you the never type's docs #49529

Closed

ollie27 mentioned this pull request Apr 5, 2018

Correct a few stability attributes #49673

Merged

uberjay mentioned this pull request Apr 9, 2018

Crash in program compiled with nightly #49275

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nikomatsakis mentioned this pull request Apr 13, 2018

revert stabilization of ! and TryFrom #49691

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Victor-Savu mentioned this pull request May 26, 2018

Tracking uninhabited types in matches #51076

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kennytm mentioned this pull request May 26, 2018

Tracking issue for RFC 1872: exhaustive_patterns feature #51085

Open

3 tasks

QuietMisdreavus mentioned this pull request Sep 13, 2018

re-mark the never docs as unstable #54207

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dtolnay mentioned this pull request Mar 8, 2023

Update the comment on simpler exhaustive matching in derive serde-rs/serde#2388

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Stabilise feature(never_type). Introduce feature(exhaustive_patterns) #47630

Stabilise feature(never_type). Introduce feature(exhaustive_patterns) #47630

canndrew commented Jan 21, 2018

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canndrew commented Jan 24, 2018

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Stabilise feature(never_type). Introduce feature(exhaustive_patterns) #47630

Stabilise feature(never_type). Introduce feature(exhaustive_patterns) #47630

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