Handle projections as uncovered types during coherence check #100555

atsuzaki · 2022-08-14T23:25:37Z

Fixes #99554. Update code to handle projections as uncovered types during coherence check/orphan check & update error messages accordingly.

rust-highfive · 2022-08-14T23:25:40Z

r? @oli-obk

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atsuzaki · 2022-08-14T23:26:04Z

r? @lcnr

compiler/rustc_typeck/src/coherence/orphan.rs

compiler/rustc_trait_selection/src/traits/coherence.rs

lcnr

there are still 2 tests where the error messages aren't quite right

please fix the error messages for them and add them as additional tests

going to start a crater run for this

compiler/rustc_typeck/src/coherence/orphan.rs

lcnr · 2022-08-15T06:28:07Z

@bors try

bors · 2022-08-15T06:28:21Z

⌛ Trying commit ba88709461a684be5ef433e2da892492ebde60b0 with merge df0acfe6d8f079d1fdd8e6b7447569d81b00f126...

bors · 2022-08-15T08:18:44Z

☀️ Try build successful - checks-actions
Build commit: df0acfe6d8f079d1fdd8e6b7447569d81b00f126 (df0acfe6d8f079d1fdd8e6b7447569d81b00f126)

lcnr · 2022-08-15T15:54:29Z

@craterbot check

craterbot · 2022-08-15T15:54:36Z

👌 Experiment pr-100555 created and queued.
🤖 Automatically detected try build df0acfe6d8f079d1fdd8e6b7447569d81b00f126
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2022-08-15T15:55:30Z

🚧 Experiment pr-100555 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2022-08-16T18:10:28Z

🎉 Experiment pr-100555 is completed!
📊 208 regressed and 4 fixed (241311 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

lcnr · 2022-08-17T07:04:05Z

ok, we have more regressions than I would like. Most of them look like they use fully concrete projections though, and these are fine.

I see two ways forward here:

simply check whether the projection contains any generic parameters and fail in that case, or
- actually recursively orphan check each projection using InCrate::Remote and consider them as non-local type if the orphan check fails and as uncovered projection/param if that orphan check succeeds.

I think recursively orphan checking projections seems like a better solution to me, so I would go with that. When encountering a projection in the type visitor, call orphan_check_trait_ref for that projection, if that fails, treat the projection as a non-local type, if it succeeds, treat it as an uncovered type.

edit: The second approach sadly does not work, as even a local impl can use a type parameter as an associated type if it's used as in input.

compiler/rustc_trait_selection/src/traits/coherence.rs

atsuzaki · 2022-08-25T01:45:25Z

src/test/ui/coherence/impl[t]-foreign[fundamental[t]]-for-foreign.stderr

   |
 LL | impl<T> Remote1<Box<T>> for u32 {
-   |      ^ type parameter `T` must be used as the type parameter for some local type
+   |                 ^^^^^^ type parameter `T` must be used as the type parameter for some local type


@lcnr This is one of the last (visual) kinks... I was able to detect the fundamental type for cases like impl<T> Remote for Box<T> where the T is at idx=0, and I can look at self_ty which is a rustc_middle::Ty.

But in this case, I only have a hir::Ty and can't figure out how it's a fundamental type from that.

urgh the link broke after rebase+force push, https://github.com/rust-lang/rust/pull/100555/files#diff-fddbd2e2a2a86430f2f013d5d787d7ad6c85427cd81a2282ac0fcc7d641733bc

…ss tests

rfcbot · 2022-09-14T16:19:03Z

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

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), 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.

rfcbot · 2022-10-03T20:38:44Z

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

nikomatsakis · 2022-10-03T21:19:48Z

@lcnr can you give a bit more details about the wasmer crate? I feel like we ought to reach out to them to discuss possible solutions, as that is a pretty broadly used crate.

nikomatsakis · 2022-10-03T21:20:25Z

cc @matklad @nagisa -- two owners of the wasmer-types crate

lcnr · 2022-10-04T09:33:31Z

The root cause seems to be the Deserialize derive from https://github.com/rkyv/rkyv.

This derive emits the following impl:

#[derive(Deserialize, Archive)]
struct Foo<T>(T);

impl<T, D> Deserialize<Foo<T>, D> for <Foo<T> as Archive>::Archived {
    // ...
}

impl<T> Archive for Foo<T> {
   type Assoc = LocalType;
}

See https://gist.github.com/lcnr/75d99bd2900f9dd2eaa558b3c68c42e2 for the full (cleaned up) output.

This could be adapted to pass the new orphan rules by switching the argument ordering of Deserialize: instead of ARCHIVE: Deserialize<TYPE, DESERIALIZER> it could be TYPE: Deserialize<ARCHIVE, DESERIALIZER>. This would be probably be the easiest fix (even if it is a breaking change for rkyv).

There are hacks which would only require a minor update of rkyv while still allowing us to error on unsound impls, e.g. by adding some #[no_uncovered_param] attribute to associated types (in the trait definition) which causes us to consider that associated type to always only be a non-local type and requires all impls to not directly use T or Fundamental<T> for it. I don't think that idea is worth it and can't think of one which is.

matklad · 2022-10-04T10:09:48Z

cc @djkoloski

djkoloski · 2022-10-04T12:49:47Z

If I'm understanding this problem correctly, this could also be addressed by emitting a concrete ARCHIVE type instead of referring to it indirectly through the Archive trait's associated type. Is that accurate? I'd have to check and make sure, but that seems more achievable for rkyv.

lcnr · 2022-10-04T13:44:19Z

yes, using the concrete type for the archive instead of an associated type works as well

djkoloski · 2022-10-04T13:58:03Z

Great, I'll take action on rkyv/rkyv#289 and cut a new release as soon as possible.

rfcbot · 2022-10-13T21:03:50Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

oli-obk · 2022-10-20T10:21:10Z

@atsuzaki could you rebase the PR and fix the conflict? I think we're ready to merge

lcnr · 2022-10-20T11:13:04Z

we still have to convert this to a future-compat lint before merging this, intend to meet with @atsuzaki to figure out how exactly this should be done

apiraino · 2023-03-29T14:28:38Z

Hi, how is this progressing? Any updates to report cc @lcnr @atsuzaki ? Thanks!

atsuzaki · 2023-03-29T15:17:53Z

@apiraino hi, I sadly no longer have time to work on this. I've spoken to @lcnr about them/someone possibly taking over this?

JohnCSimon · 2023-05-28T13:50:35Z

@atsuzaki

Ping from triage: I'm closing this due to inactivity, Please reopen when you are ready to continue with this.
Note: if you are going to continue please open the PR BEFORE you push to it, else you won't be able to reopen - this is a quirk of github.
Thanks for your contribution.

@rustbot label: +S-inactive

Normalize trait ref before orphan check & consider ty params in alias types to be uncovered Fixes rust-lang#99554, fixes rust-lang/types-team#104. Supersedes rust-lang#100555. r? lcnr

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atsuzaki commented Aug 25, 2022

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atsuzaki requested a review from lcnr August 25, 2022 01:54

atsuzaki added 3 commits August 24, 2022 18:57

Update coherence check for projections, add test

56c2886

Blessing new error message for existing coherence tests

e6bf058

Change error msg wording from type projection -> associated type, ble…

1ac08d8

…ss tests

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Sep 14, 2022

lcnr 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 Sep 21, 2022

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 Oct 3, 2022

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JohnCSimon closed this May 28, 2023

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fmease mentioned this pull request Dec 6, 2023

Normalize trait ref before orphan check & consider ty params in alias types to be uncovered #117164

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Handle projections as uncovered types during coherence check #100555

Handle projections as uncovered types during coherence check #100555

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Handle projections as uncovered types during coherence check #100555

Handle projections as uncovered types during coherence check #100555

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