Delay replacing escaping bound vars in `FindParamInClause` #142441

compiler-errors · 2025-06-12T23:46:22Z

By uplifting the BoundVarReplacer, which is used by (e.g.) normalization to replace escaping bound vars that are encountered when folding binders, we can use a similar strategy to delay the instantiation of a binder's contents in the FindParamInClause used by the new trait solver.

This should alleviate the recently added requirement that Binder<T>: TypeVisitable only if T: TypeFoldable, which was previously required b/c we were calling enter_forall so that we could structurally normalize aliases that we found within the predicates of a param-env clause.

r? lcnr

rustbot · 2025-06-12T23:46:28Z

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

HIR ty lowering was modified

cc @fmease

compiler-errors · 2025-06-12T23:46:37Z

compiler/rustc_trait_selection/src/traits/util.rs

@@ -219,7 +219,7 @@ pub struct BoundVarReplacer<'a, 'tcx> {
    // the `var` (but we *could* bring that into scope if we were to track them as we pass them).
    mapped_regions: FxIndexMap<ty::PlaceholderRegion, ty::BoundRegion>,
    mapped_types: FxIndexMap<ty::PlaceholderType, ty::BoundTy>,
-    mapped_consts: BTreeMap<ty::PlaceholderConst, ty::BoundVar>,
+    mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundVar>,


compiler-errors · 2025-06-12T23:47:24Z

compiler/rustc_type_ir/src/binder.rs

@@ -128,7 +128,7 @@ impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Binder<I, T> {
    }
 }

-impl<I: Interner, T: TypeFoldable<I>> TypeVisitable<I> for Binder<I, T> {
+impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Binder<I, T> {


This is the motivation for this PR.

compiler-errors · 2025-06-12T23:47:39Z

@bors2 try @rust-timer queue

rust-bors · 2025-06-12T23:47:42Z

⌛ Trying commit 216d418 with merge e40247b…

To cancel the try build, run the command @bors2 try cancel.

…r=<try> Delay replacing escaping bound vars in `FindParamInClause` By uplifting the `BoundVarReplacer`, which is used by (e.g.) normalization to replace escaping bound vars that are encountered when folding binders, we can use a similar strategy to delay the instantiation of a binder's contents in the `FindParamInClause` used by the new trait solver. This should alleviate the recently added requirement that `Binder<T>: TypeVisitable` only if `T: TypeFoldable`, which was previously required b/c we were calling `enter_forall` so that we could structurally normalize aliases that we found within the predicates of a param-env clause. r? lcnr

rust-bors · 2025-06-13T02:15:42Z

☀️ Try build successful (CI)
Build commit: e40247b (e40247b5a92c0ac9c7ab5a973a92d309f9640d67, parent: 573a01569000d395498a5f98f916d6e5305ac81a)

rust-timer · 2025-06-13T09:07:27Z

Finished benchmarking commit (e40247b): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

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

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	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	9.4%	[9.4%, 9.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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Bootstrap: 754.801s -> 755.78s (0.13%)
Artifact size: 372.21 MiB -> 372.13 MiB (-0.02%)

… type abstraction

compiler-errors · 2025-06-13T17:55:54Z

fixed clippy

lcnr · 2025-06-13T19:36:28Z

@bors r+

bors · 2025-06-13T19:36:31Z

📌 Commit b138202 has been approved by lcnr

It is now in the queue for this repository.

lcnr · 2025-06-13T19:36:36Z

@bors rollup=always

Rollup of 16 pull requests Successful merges: - #140969 (Allow initializing logger with additional tracing Layer) - #141352 (builtin dyn impl no guide inference) - #142046 (add Vec::peek_mut) - #142273 (tests: Minicore `extern "gpu-kernel"` feature test) - #142302 (Rework how the disallowed qualifier in function type diagnostics are generated) - #142405 (Don't hardcode the intrinsic return types twice in the compiler) - #142434 ( Pre-install JS dependencies in tidy Dockerfile) - #142439 (doc: mention that intrinsics should not be called in user code) - #142441 (Delay replacing escaping bound vars in `FindParamInClause`) - #142449 (Require generic params for const generic params) - #142452 (Remove "intermittent" wording from `ReadDir`) - #142459 (Remove output helper bootstrap) - #142460 (cleanup search graph impl) - #142461 (compiletest: Clarify that `--no-capture` is needed with `--verbose`) - #142475 (Add platform support docs & maintainers for *-windows-msvc) - #142480 (tests: Convert two handwritten minicores to add-core-stubs) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #142441 - compiler-errors:lazier-binder-value-folding, r=lcnr Delay replacing escaping bound vars in `FindParamInClause` By uplifting the `BoundVarReplacer`, which is used by (e.g.) normalization to replace escaping bound vars that are encountered when folding binders, we can use a similar strategy to delay the instantiation of a binder's contents in the `FindParamInClause` used by the new trait solver. This should alleviate the recently added requirement that `Binder<T>: TypeVisitable` only if `T: TypeFoldable`, which was previously required b/c we were calling `enter_forall` so that we could structurally normalize aliases that we found within the predicates of a param-env clause. r? lcnr

rustbot assigned lcnr Jun 12, 2025

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 Jun 12, 2025

compiler-errors commented Jun 12, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 13, 2025

compiler-errors added 5 commits June 13, 2025 17:54

Don't use BTreeMap for mapped_consts

86497e6

Make connection between Placeholder and Bound a bit more clear in the…

fe92efa

… type abstraction

Uplift BoundVarReplacer

6fa6d0e

Replace escaping bound vars in ty/ct visiting, not binder visiting

da8d529

TypeVisiting binders no longer requires TypeFolding its interior

b138202

compiler-errors force-pushed the lazier-binder-value-folding branch from 216d418 to b138202 Compare June 13, 2025 17:55

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 Jun 13, 2025

workingjubilee mentioned this pull request Jun 14, 2025

Rollup of 16 pull requests #142483

Merged

bors merged commit c3537c2 into rust-lang:master Jun 14, 2025
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rustbot added this to the 1.89.0 milestone Jun 14, 2025

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Delay replacing escaping bound vars in `FindParamInClause` #142441

Delay replacing escaping bound vars in `FindParamInClause` #142441