borrowck: Represent 'best blame constraint' as index into Vec<OutlivesConstraint>#158623
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borrowck: Represent 'best blame constraint' as index into Vec<OutlivesConstraint>#158623Enselic wants to merge 4 commits into
Vec<OutlivesConstraint>#158623Enselic wants to merge 4 commits into
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…g new one
So that we in an upcoming commit can return the index into path instead
of a "duplicate".
This passes:
./x test --bless tests/ui --keep-stage-std 1 --set rust.deny-warnings=false
…esConstraint>` This makes the code simpler and easier to understand, since we don't have to partially copy an `OutlivesConstraint` into the `BlameConstraint` struct (which we can remove entirely) and the `BorrowExplanation::MustBeValidFor` enum variant (which we can simplify). Instead, we reference the "best" `OutlivesConstraint` by an index into `Vec<OutlivesConstraint>`. This is not only simpler, it also opens up the possibility for diagnostics to access the full `OutlivesConstraint` info.
jhpratt
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…ath, r=JohnTitor borrowck: Introduce BlameConstraint::to_obligation_cause_from_path() Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`. The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is. For reference, `ObligationCause` was introdued by rust-lang#89249, but the codebase looked quite different back then. This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in rust-lang#158623. # Notes I have removed the comment ```rs // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint. // Instead, we use it to produce an improved `ObligationCauseCode`. ```` because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient: ```rs // We handle predicates and opaque types specially; don't prioritize them here. ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4, ```
JonathanBrouwer
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…ath, r=JohnTitor borrowck: Introduce BlameConstraint::to_obligation_cause_from_path() Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`. The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is. For reference, `ObligationCause` was introdued by rust-lang#89249, but the codebase looked quite different back then. This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in rust-lang#158623. # Notes I have removed the comment ```rs // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint. // Instead, we use it to produce an improved `ObligationCauseCode`. ```` because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient: ```rs // We handle predicates and opaque types specially; don't prioritize them here. ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4, ```
JonathanBrouwer
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…ath, r=JohnTitor borrowck: Introduce BlameConstraint::to_obligation_cause_from_path() Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`. The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is. For reference, `ObligationCause` was introdued by rust-lang#89249, but the codebase looked quite different back then. This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in rust-lang#158623. # Notes I have removed the comment ```rs // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint. // Instead, we use it to produce an improved `ObligationCauseCode`. ```` because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient: ```rs // We handle predicates and opaque types specially; don't prioritize them here. ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4, ```
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☔ The latest upstream changes (presumably #158811) made this pull request unmergeable. Please resolve the merge conflicts by rebasing. |
rust-timer
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Rollup merge of #158624 - Enselic:to_obligation_cause_from_path, r=JohnTitor borrowck: Introduce BlameConstraint::to_obligation_cause_from_path() Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`. The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is. For reference, `ObligationCause` was introdued by #89249, but the codebase looked quite different back then. This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in #158623. # Notes I have removed the comment ```rs // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint. // Instead, we use it to produce an improved `ObligationCauseCode`. ```` because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient: ```rs // We handle predicates and opaque types specially; don't prioritize them here. ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4, ```
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This makes the code simpler and easier to understand, since we don't have to partially copy an
OutlivesConstraintinto theBlameConstraintstruct (which we can remove entirely) and theBorrowExplanation::MustBeValidForenum variant (which we can simplify).Instead, we reference the "best"
OutlivesConstraintby an index intoVec<OutlivesConstraint>. This is not only simpler, it also opens up the possibility for diagnostics to access the fullOutlivesConstraintinfo.I discovered this cleanup while investigating ways to solve #138408.
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This PR is not ready for review. I will split this up into smaller PRs for easier review. The purpose of this PR is to: