Fix checking of auto trait bounds in trait objects. #45772

leoyvens · 2017-11-05T00:03:46Z

Any auto trait is allowed in trait object bounds. Fix duplicate check of type and lifetime parameter count, which we were emitting twice.

Note: This was the last use of Send in the compiler, meaning after a new stage0 we could remove the send lang item.

Any auto trait is allowed in trait object bounds. Fix duplicate check of type and lifetime parameter count.

rust-highfive · 2017-11-05T00:03:58Z

r? @nikomatsakis

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nikomatsakis

Code looks nice.

nikomatsakis · 2017-11-06T18:17:31Z

src/librustc_typeck/astconv.rs

-                } else {
-                    false
-                }
+            Def::Trait(trait_did) if tcx.trait_is_auto(trait_did) => {


In principle we could easily extend this to arbitrary marker traits, I suppose?

nikomatsakis · 2017-11-06T18:18:32Z

Note: This was the last use of Send in the compiler, meaning after a new stage0 we could remove the send lang item.

~~Could we do it now, and just use #[cfg_attr(stage0, lang)]?~~

Oh, I guess that's annoying, for same reason as before. Forgive me, old habits die hard. =)

nikomatsakis · 2017-11-06T18:26:58Z

OK -- thought this over. I don't think extending to arbitrary marker traits is something we can do without an RFC. But auto traits should be ok, since defining new auto traits is still unstable.

nikomatsakis · 2017-11-06T18:28:30Z

Well, there are a few auto traits that are stable and are not Send nor Sync (e.g. UnwindSafe). I'm going to ask @rust-lang/lang team for an FCP here, just to play it safe.

nikomatsakis · 2017-11-06T18:32:53Z

@bors fcp merge

I'd like to propose that we merge this PR. It has the effect of enabling trait objects with arbitrary auto traits composed together. So, whereas before you could only do dyn (Trait + Send), you can now do dyn (Trait + Send + UnwindSafe), for example. I think this makes sense logically, and it fits with the oft-expressed intention to permit arbitrary object-safe traits to be composed (e.g., dyn (Foo + Bar)).

I don't feel an RFC is needed for this particular PR. However, to go further and support composition of arbitrary object-safe traits, I would like to have an RFC. This is not because I expect us to be against the basic idea, but just because there are various approaches we might take (e.g., I favor multiple vtables, but a case can be made for a single composed vtable) and I think it would benefit from a proper design cycle.

The change as implemented is "insta-stable". If we wanted, we could also make arbitrary extensions to the capabilities here, but require a feature-gate to go beyond Send/Sync. This might actually be better, so feel free to object if you think it would be.

leoyvens · 2017-11-06T19:36:09Z

@nikomatsakis I think you meant to invoke @rfcbot.

withoutboats · 2017-11-06T20:37:34Z

@rfcbot fcp merge

rfcbot · 2017-11-06T20:37:35Z

Team member @withoutboats has proposed to merge this. The next step is review by the rest of the tagged teams:

No concerns currently listed.

Once these reviewers reach consensus, this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

eddyb · 2017-11-06T20:45:12Z

Oh, I guess that's annoying, for same reason as before. Forgive me, old habits die hard. =)

Wait, what's the explanation here?

leoyvens · 2017-11-06T20:52:52Z

@eddyb If we do it I imagine that when the stage0 is updated the build would start failing because the new stage0 dosen't know the send lang item.

eddyb · 2017-11-06T20:54:33Z

@leodasvacas But that's standard procedure - whoever updates the bootstrap compiler removes all the cfg{,_attr}(stage0) annotations.

leoyvens · 2017-11-06T20:56:21Z

@eddyb Ah, I was ignorant on the process here. I'll do it then.

cramertj · 2017-11-06T22:39:31Z

@rfcbot reviewed

It's completely unused.

leoyvens · 2017-11-07T12:56:54Z

Removed the send lang item.

rfcbot · 2017-11-09T20:07:55Z

🔔 This is now entering its final comment period, as per the review above. 🔔

nikomatsakis · 2017-11-09T20:17:52Z

@bors r+

bors · 2017-11-09T20:17:53Z

📌 Commit 7995f87 has been approved by nikomatsakis

nikomatsakis · 2017-11-09T20:18:02Z

@bors r-

nikomatsakis · 2017-11-09T20:18:11Z

Guess I should show some decorum and wait a bit for FCP.

nikomatsakis · 2017-11-10T17:21:34Z

@bors r+

I'm impatient. We can always back it out if something dramatic comes up.

bors · 2017-11-10T17:21:36Z

📌 Commit 7995f87 has been approved by nikomatsakis

bors · 2017-11-11T00:09:36Z

⌛ Testing commit 7995f87 with merge e33731286e7e57b67375218bb3024caa93d4a530...

bors · 2017-11-11T02:06:06Z

💔 Test failed - status-travis

kennytm · 2017-11-11T02:23:40Z

@bors retry

[01:13:14] test process::tests::test_process_output_fail_to_start has been running for over 60 seconds


No output has been received in the last 30m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received

The build has been terminated

bors · 2017-11-11T04:33:10Z

⌛ Testing commit 7995f87 with merge e528c7e...

…r=nikomatsakis Fix checking of auto trait bounds in trait objects. Any auto trait is allowed in trait object bounds. Fix duplicate check of type and lifetime parameter count, which we were [emitting twice](https://play.rust-lang.org/?gist=37dbbdbbec62dec423bb8f6d92f137cc&version=stable). Note: This was the last use of `Send` in the compiler, meaning after a new `stage0` we could remove the `send` lang item.

bors · 2017-11-11T07:33:27Z

💔 Test failed - status-travis

kennytm · 2017-11-11T09:00:47Z

@bors retry

dist-arm-linux 3-hour timed out?

bors · 2017-11-11T09:56:28Z

⌛ Testing commit 7995f87 with merge 69ee5a8...

…r=nikomatsakis Fix checking of auto trait bounds in trait objects. Any auto trait is allowed in trait object bounds. Fix duplicate check of type and lifetime parameter count, which we were [emitting twice](https://play.rust-lang.org/?gist=37dbbdbbec62dec423bb8f6d92f137cc&version=stable). Note: This was the last use of `Send` in the compiler, meaning after a new `stage0` we could remove the `send` lang item.

bors · 2017-11-11T12:13:42Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 69ee5a8 to master...

leoyvens · 2017-11-13T21:49:36Z

@gbutler69 It was removed because it was no longer in use. Keeping lang items to a minimal is good.

Fix checking of auto trait bounds in trait objects.

f46f388

Any auto trait is allowed in trait object bounds. Fix duplicate check of type and lifetime parameter count.

rust-highfive assigned nikomatsakis Nov 5, 2017

kennytm added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-lang Relevant to the language team, which will review and decide on the PR/issue. labels Nov 5, 2017

nikomatsakis approved these changes Nov 6, 2017

View reviewed changes

rfcbot added the proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. label Nov 6, 2017

kennytm added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 7, 2017

Remove send lang item.

7995f87

It's completely unused.

eddyb added the relnotes Marks issues that should be documented in the release notes of the next release. label Nov 7, 2017

rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Nov 9, 2017

kennytm 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-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). labels Nov 10, 2017

bors merged commit 7995f87 into rust-lang:master Nov 11, 2017

leoyvens mentioned this pull request Nov 13, 2017

Remove the unnecessary lang items for Send and Sync #28326

Closed

leoyvens deleted the fix-auto-bounds-in-trait-objects branch November 17, 2017 18:09

petrochenkov mentioned this pull request Nov 28, 2017

Updated RELEASES.md for 1.23.0 #46327

Merged

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Fix checking of auto trait bounds in trait objects. #45772

Fix checking of auto trait bounds in trait objects. #45772

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Fix checking of auto trait bounds in trait objects. #45772

Fix checking of auto trait bounds in trait objects. #45772

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