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Don't immediately error for cycles during normalization #75494

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merged 1 commit into from
Aug 20, 2020
Merged

Don't immediately error for cycles during normalization #75494

merged 1 commit into from
Aug 20, 2020

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matthewjasper
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#73452 meant some normalization cycles could be detected earlier, breaking some code.
This PR makes defers errors for normalization cycles to fulfillment, fixing said code.

Fixes #74868

r? @nikomatsakis

@matthewjasper matthewjasper added beta-nominated Nominated for backporting to the compiler in the beta channel. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 13, 2020
@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 13, 2020
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@bors p=1

Once approved we want this to be in ASAP.

nikomatsakis
nikomatsakis approved these changes Aug 20, 2020
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OK, I understand the strategy now, it's not once I had ever considered. Interesting. Also, a good example to try throwing at chalk, I've been wanting to create realistic examples of cycles (or near cycles) that arise during projection.

src/librustc_trait_selection/traits/project.rs
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &PolyProjectionObligation<'tcx>,
) -> Result<Option<Vec<PredicateObligation<'tcx>>>, MismatchedProjectionTypes<'tcx>> {
) -> Result<
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Nit: this is a complex return type! I thnk the doc comment could be extended to explain what the various return values mean.

src/librustc_trait_selection/traits/fulfill.rs
// Let the caller handle the recursion
Ok(Err(project::InProgress)) => ProcessResult::Changed(mk_pending(vec![
project_obligation.with(project_obligation.predicate.to_predicate(tcx)),
])),
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ok, I see, so we basically just push the project predicate back up to the caller... interesting...

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@bors r+

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bors commented Aug 20, 2020

📌 Commit 8e81710685349464553b30c0a7e89c50eb4d3b24 has been approved by nikomatsakis

@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 Aug 20, 2020
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Er, @bors r-

r=me with the nit addressed

@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 Aug 20, 2020
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Or just r+ if we think it's important enough

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heavily discussed in T-compiler meeting.

This is a subtle change to subtle code. We've also agreed on backporting it and fire a crater run as soon as possible, which probably won't be on time but would give as an advantage to act quickly if there are bad consequences.

@rustbot modify labels: beta-accepted

@rustbot rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Aug 20, 2020
@matthewjasper matthewjasper force-pushed the defer-recursive-projection-error branch from 8e81710 to 67fb583 Compare August 20, 2020 18:30
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@bors r=nikomatsakis

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bors commented Aug 20, 2020

📌 Commit 67fb583 has been approved by nikomatsakis

@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 Aug 20, 2020
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bors commented Aug 20, 2020

⌛ Testing commit 67fb583 with merge e15510c...

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bors commented Aug 20, 2020

☀️ Test successful - checks-actions, checks-azure
Approved by: nikomatsakis
Pushing e15510c to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Aug 20, 2020
@bors bors merged commit e15510c into rust-lang:master Aug 20, 2020
@matthewjasper matthewjasper deleted the defer-recursive-projection-error branch August 21, 2020 07:04
@Mark-Simulacrum Mark-Simulacrum removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Aug 21, 2020
This was referenced Aug 21, 2020
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Your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log. 
##[section]Starting: Request a runner to run this job
Found online and idle self-hosted runner in current repository that matches the required labels: 'self-hosted , ARM64 , linux'

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @rust-lang/infra. (Feature Requests)

@jruderman jruderman mentioned this pull request Dec 4, 2022
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@cuviper cuviper added this to the 1.47.0 milestone May 2, 2024
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Unexpected trait resolution overflow error
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@matthewjasper @spastorino @nikomatsakis @bors @rust-log-analyzer @cuviper @Mark-Simulacrum @rust-highfive @rustbot