borrowck: Keep returned `path` from `best_blame_constraint()` consistent by Enselic · Pull Request #158877 · rust-lang/rust

Enselic · 2026-07-06T18:47:49Z

The function fn best_blame_constraint() returns a Vec<OutlivesConstraint> and a BlameConstraint. The BlameConstraint is really just a slimmed down version of an OutlivesConstraint. So we can remove BlameConstraint entirely and instead return Vec<OutlivesConstraint> and an index into that Vec. (Encapsulated in a struct for nice ergonomics.)

To prepare for that, change the code to adjust Vec<OutlivesConstraint> in-place and return info about the adjusted element, rather than returning info for a newly created "fake" OutlivesConstraint.

It is slightly sad that we make path mut, but I think we can live with that. Diagnostics tests will surely catch if someone messes up because of that.

This takes us one step closer (this is commit 2 of 4) towards the end result illustrated in #158623.

The function `fn best_blame_constraint()` returns a `Vec<OutlivesConstraint>` and a `BlameConstraint`. The `BlameConstraint` is really just a slimmed down version of an `OutlivesConstraint`. So we can remove `BlameConstraint` entirely and instead return `Vec<OutlivesConstraint>` and an index into that `Vec`. (Encapsulated in a struct for nice ergonomics.) To prepare for that, change the code to adjust `Vec<OutlivesConstraint>` in-place and return info about the adjusted element, rather than returning info for a newly created "fake" `OutlivesConstraint`.

rustbot · 2026-07-06T18:47:54Z

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fee1-dead · 2026-07-09T19:53:43Z

@bors r+ rollup

rust-bors · 2026-07-09T19:53:46Z

📌 Commit 6741efa has been approved by fee1-dead

It is now in the queue for this repository.

…nt, r=fee1-dead borrowck: Keep returned `path` from `best_blame_constraint()` consistent The function `fn best_blame_constraint()` returns a `Vec<OutlivesConstraint>` and a `BlameConstraint`. The `BlameConstraint` is really just a slimmed down version of an `OutlivesConstraint`. So we can remove `BlameConstraint` entirely and instead return `Vec<OutlivesConstraint>` and an index into that `Vec`. (Encapsulated in a struct for nice ergonomics.) To prepare for that, change the code to adjust `Vec<OutlivesConstraint>` in-place and return info about the adjusted element, rather than returning info for a newly created "fake" `OutlivesConstraint`. It is slightly sad that we make `path` `mut`, but I think we can live with that. Diagnostics tests will surely catch if someone messes up because of that. This takes us one step closer (this is commit 2 of 4) towards the end result illustrated in rust-lang#158623.

…uwer Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes)

…nt, r=fee1-dead borrowck: Keep returned `path` from `best_blame_constraint()` consistent The function `fn best_blame_constraint()` returns a `Vec<OutlivesConstraint>` and a `BlameConstraint`. The `BlameConstraint` is really just a slimmed down version of an `OutlivesConstraint`. So we can remove `BlameConstraint` entirely and instead return `Vec<OutlivesConstraint>` and an index into that `Vec`. (Encapsulated in a struct for nice ergonomics.) To prepare for that, change the code to adjust `Vec<OutlivesConstraint>` in-place and return info about the adjusted element, rather than returning info for a newly created "fake" `OutlivesConstraint`. It is slightly sad that we make `path` `mut`, but I think we can live with that. Diagnostics tests will surely catch if someone messes up because of that. This takes us one step closer (this is commit 2 of 4) towards the end result illustrated in rust-lang#158623.

Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158541 (Move `std::io::Write` to `core::io`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158960 (Fix bootstrap submodule path prefix matching) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes) - #159036 (bootstrap: expand '@argfile' arguments to rustc shim)

Rollup merge of #158877 - Enselic:adjust-best_blame_constraint, r=fee1-dead borrowck: Keep returned `path` from `best_blame_constraint()` consistent The function `fn best_blame_constraint()` returns a `Vec<OutlivesConstraint>` and a `BlameConstraint`. The `BlameConstraint` is really just a slimmed down version of an `OutlivesConstraint`. So we can remove `BlameConstraint` entirely and instead return `Vec<OutlivesConstraint>` and an index into that `Vec`. (Encapsulated in a struct for nice ergonomics.) To prepare for that, change the code to adjust `Vec<OutlivesConstraint>` in-place and return info about the adjusted element, rather than returning info for a newly created "fake" `OutlivesConstraint`. It is slightly sad that we make `path` `mut`, but I think we can live with that. Diagnostics tests will surely catch if someone messes up because of that. This takes us one step closer (this is commit 2 of 4) towards the end result illustrated in #158623.

JonathanBrouwer · 2026-07-10T12:57:13Z

@rust-timer build a98949b

rust-timer · 2026-07-10T15:39:03Z

Finished benchmarking commit (a98949b): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.3%]	2
Regressions ❌ (secondary)	0.1%	[0.0%, 0.2%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	3
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	2

Max RSS (memory usage)

Results (primary -3.6%, secondary -2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.6%	[-3.6%, -3.6%]	1
Improvements ✅ (secondary)	-2.0%	[-3.4%, -1.3%]	3
All ❌✅ (primary)	-3.6%	[-3.6%, -3.6%]	1

Cycles

Results (secondary -0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.1%	[2.3%, 9.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.5%	[-9.0%, -1.5%]	7
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 490.768s -> 492.209s (0.29%)
Artifact size: 389.74 MiB -> 389.13 MiB (-0.16%)

JonathanBrouwer · 2026-07-10T15:46:31Z

@rustbot label: +perf-regression-triaged
Noise

rustbot assigned fee1-dead Jul 6, 2026

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. labels Jul 6, 2026

Enselic mentioned this pull request Jul 6, 2026

borrowck: Represent 'best blame constraint' as index into Vec<OutlivesConstraint> #158623

Draft

rust-bors Bot 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 Jul 9, 2026

JonathanBrouwer mentioned this pull request Jul 9, 2026

Rollup of 24 pull requests #159037

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This was referenced Jul 9, 2026

Rollup of 25 pull requests #159045

Closed

Rollup of 24 pull requests #159046

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rust-bors Bot merged commit fb6879d into rust-lang:main Jul 10, 2026
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rustbot added this to the 1.99.0 milestone Jul 10, 2026

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rustbot added the perf-regression Performance regression. label Jul 10, 2026

rustbot added the perf-regression-triaged The performance regression has been triaged. label Jul 10, 2026

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borrowck: Keep returned `path` from `best_blame_constraint()` consistent#158877

borrowck: Keep returned `path` from `best_blame_constraint()` consistent#158877
rust-bors[bot] merged 1 commit into
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Enselic:adjust-best_blame_constraint

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Overall result: ❌✅ regressions and improvements - please read:

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