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Fudge infer vars in the cause code of Obligation intentionally - #149299

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Fudge infer vars in the cause code of Obligation intentionally#149299
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@adwinwhiteadwinwhite commented Nov 25, 2025•
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Fixes the ICE variant in rust-lang/trait-system-refactor-initiative#245.
Fixes#142866.

The detailed cause is in the test comments.

r? @lcnr

@rustbotrustbot 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 Nov 25, 2025
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lcnr
lcnr reviewed Nov 27, 2025
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Comment threadcompiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs Outdated
try_borrowing(cause.derived.parent_trait_pred, &[])
// Parent trait predicate may contain regions that's already popped since `cause`
// in `Obligation` is ignored by folders/visitors.
// We can erase them since evaluation later doesn't care about regions anyway.

@lcnrlcnrNov 27, 2025

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is that because the BestObligation folder happens inside of a fudge? and would eagerly fudging the cause there as well also avoid this ICE?

@adwinwhiteadwinwhiteNov 27, 2025•
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It's because of the definition of Obligation. So the region vars in cause is ignored in fudge_inference_if_ok.

@lcnrlcnrNov 27, 2025

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yes, but the fudge when computing the best obligation could take (Predicate, Cause) as the return type instead of a full obligation to properly fudge the cause there

@lcnrlcnr 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 Nov 27, 2025
@adwinwhiteadwinwhite changed the title Erase leaked regions in cause code when giving suggestionFudge infer vars in the cause code of Obligation intentionallyNov 28, 2025
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adwinwhite commented Nov 28, 2025

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@rustbot ready

@rustbotrustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 28, 2025
@ShoyuVanilla

ShoyuVanilla commented Nov 28, 2025

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This fixes #142866 as well 👍

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rustbot commented Nov 28, 2025

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Some changes occurred to the core trait solver

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

lcnr
lcnr reviewed Nov 28, 2025
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hm, can you move both tests to traits/error-reporting?

also, can you add a fixme to Obligation that we shouldn't ignore the cause but instead change teh affected visitors to only visit predicates manually :>

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lcnr commented Dec 1, 2025

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@bors r+ rollup

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bors commented Dec 1, 2025

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📌 Commit b111aed has been approved by lcnr

It is now in the queue for this repository.

@borsbors 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 Dec 1, 2025
@matthiaskrgrmatthiaskrgr mentioned this pull request Dec 1, 2025
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bors added a commit that referenced this pull request Dec 1, 2025
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Auto merge of#149510- matthiaskrgr:rollup-5rt6o7z, r=matthiaskrgr
a463b0e
Rollup of 9 pull requests
Successful merges:
- #148690 (Implement `clamp_magnitude` method for primitive floats & signed integers)
- #149102 (stabilize maybe_uninit_slice)
- #149269 (cmse: do not calculate the layout of a type with infer types)
- #149299 (Fudge infer vars in the cause code of `Obligation` intentionally)
- #149344 (Don't suggest unwrap for Result in const)
- #149358 (fix(parse): Limit frontmatter fences to 255 dashes )
- #149445 (make assoc fn inherit const stability from inherent `const impl` blocks)
- #149479 (Fix indent in E0591.md)
- #149496 (Fix#148889: Add label rib when visiting delegation body)
r? `@ghost`
`@rustbot` modify labels: rollup
@bors
bors merged commit b8336a5 into rust-lang:mainDec 1, 2025
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@rustbotrustbot added this to the 1.93.0 milestone Dec 1, 2025
rust-timer added a commit that referenced this pull request Dec 1, 2025
@rust-timer
Unrolled build for#149299
904b6fc
Rollup merge of #149299 - adwinwhite:next-245-ice, r=lcnr
Fudge infer vars in the cause code of `Obligation` intentionally
Fixes the ICE variant in rust-lang/trait-system-refactor-initiative#245.
Fixes#142866.
The detailed cause is in the test comments.
r? `@lcnr`
github-actionsBot pushed a commit to rust-lang/rust-analyzer that referenced this pull request Dec 15, 2025
@bors
Auto merge of #149510 - matthiaskrgr:rollup-5rt6o7z, r=matthiaskrgr
9b730b7
Rollup of 9 pull requests
Successful merges:
- rust-lang/rust#148690 (Implement `clamp_magnitude` method for primitive floats & signed integers)
- rust-lang/rust#149102 (stabilize maybe_uninit_slice)
- rust-lang/rust#149269 (cmse: do not calculate the layout of a type with infer types)
- rust-lang/rust#149299 (Fudge infer vars in the cause code of `Obligation` intentionally)
- rust-lang/rust#149344 (Don't suggest unwrap for Result in const)
- rust-lang/rust#149358 (fix(parse): Limit frontmatter fences to 255 dashes )
- rust-lang/rust#149445 (make assoc fn inherit const stability from inherent `const impl` blocks)
- rust-lang/rust#149479 (Fix indent in E0591.md)
- rust-lang/rust#149496 (Fixrust-lang/rust#148889: Add label rib when visiting delegation body)
r? `@ghost`
`@rustbot` modify labels: rollup
@lcnrlcnr mentioned this pull request Dec 15, 2025
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