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change definitely unproductive cycles to error #137314

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Merged
merged 2 commits into from
Mar 12, 2025
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change definitely unproductive cycles to error #137314

merged 2 commits into from
Mar 12, 2025

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@lcnr lcnr commented Feb 20, 2025 •
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builds on top of #136824 by adding a third variant to PathKind for paths which may change to be coinductive in the future but must not be so right now. Most notably, impl where-clauses of not yet coinductive traits.

With this, we can change cycles which are definitely unproductive to a proper error. This fixes rust-lang/trait-system-refactor-initiative#114. This does not affect stable as we keep these cycles as ambiguous during coherence.

r? @compiler-errors @nikomatsakis

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Feb 20, 2025
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@lcnr lcnr force-pushed the cycles-with-unknown-kind branch from 908a6ad to 25621e4 Compare February 20, 2025 14:58
This was referenced Feb 20, 2025
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bors commented Feb 23, 2025

☔ The latest upstream changes (presumably #137466) made this pull request unmergeable. Please resolve the merge conflicts.

@lcnr lcnr changed the title Change definitely unproductive cycles to error change definitely unproductive cycles to error Feb 26, 2025
@lcnr lcnr force-pushed the cycles-with-unknown-kind branch 3 times, most recently from dc88ce2 to da01707 Compare February 27, 2025 11:06
@lcnr lcnr marked this pull request as ready for review February 27, 2025 11:06
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rustbot commented Feb 27, 2025

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

@lcnr lcnr force-pushed the cycles-with-unknown-kind branch 3 times, most recently from c6ab624 to fa26c12 Compare February 27, 2025 11:13
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lcnr commented Feb 27, 2025
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  • better document Inductive goal sources, explain WHY that's correct and the that it's safer to be Unknown
  • this impacts coherence, write test

@lcnr lcnr force-pushed the cycles-with-unknown-kind branch 2 times, most recently from b81c189 to fc8a474 Compare February 28, 2025 11:40
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lcnr commented Feb 28, 2025 •
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I've changed the approach to keep known inductive cycles as ambig as coherence and added a test which will be affected if we change this in the future. As coherence is already stable I would like to give this some time to make sure we're confident in the approach and to allow us to iterate further here without needing to FCP each change while it's still in flux.

I would like to do one 'complete' FCP for cycle handling before stabilizing -Znext-solver=globally. This FCP can then also be used to enable this behavior for coherence.

@lcnr lcnr force-pushed the cycles-with-unknown-kind branch from 233fd9a to 18809a2 Compare March 5, 2025 09:16
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ty for the comments

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@bors r+

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bors commented Mar 10, 2025

📌 Commit 18809a2 has been approved by compiler-errors

It is now in the queue for this repository.

@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 Mar 10, 2025
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@bors bors merged commit d55e2e4 into rust-lang:master Mar 12, 2025
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@rustbot rustbot added this to the 1.87.0 milestone Mar 12, 2025
@lcnr lcnr deleted the cycles-with-unknown-kind branch March 13, 2025 08:18
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S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver)
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inductive cycles as ambig causes unintended breakage
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