`-Znext-solver` Ignore region constraints from the nested goals in leakcheck by ShoyuVanilla · Pull Request #155749 · rust-lang/rust

ShoyuVanilla · 2026-04-24T16:56:57Z

Fixes rust-lang/trait-system-refactor-initiative#251
Fixes #140577
Fixes #153596

Canonicalize free regions from inputs as placeholders in root univ Context: The box named *coroutine witness Send lifetime requirements now considered by leakcheck* [this roadmap](https://raw.githubusercontent.com/hexcatnl/roadmap/e380fef94b47c02a056b4c8f05124a9db475b990/next-solver.svg) Fixes (only for the next-solver) #106569 Prerequisite of #155749

ShoyuVanilla · 2026-04-30T03:23:16Z

r? lcnr

rustbot · 2026-04-30T03:23:22Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

Some changes occurred to the core trait solver

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

changes to the core type system

cc @lcnr

lcnr · 2026-04-30T07:17:46Z

-                            .for_each(|c| each_edge(c.sub, c.sup));
+                        region_constraints.data().constraints[i].0.iter_outlives().for_each(
+                            |Constraint { kind: _, sub, sup, visible_for_leak_check }| {
+                                each_edge(sub, sup, visible_for_leak_check)


maybe don't even provide any constraints that are not visible to leak hceck to each_edge, feels cleaner to me,
i.e.

Suggested change

each_edge(sub, sup, visible_for_leak_check)

match visible_for_leak_check {

ty::VisibleForLeakCheck::Yes =>

each_edge(sub, sup),

ty::VisibleForLeakCheck::No => {}

}

View changes since the review

lcnr · 2026-04-30T07:19:43Z

+pub type QueryRegionConstraint<'tcx> =
+    (ty::RegionConstraint<'tcx>, ConstraintCategory<'tcx>, ty::VisibleForLeakCheck);


not in this PR, but mind adding a FIXME: Convert this into a struct

View changes since the review

lcnr · 2026-04-30T07:20:44Z

+        // We ignore constraints from the nested goals in leak check. This is to match
+        // with the old solver's behavior, which has separated evaluation and fulfillment,
+        // and the former doesn't consider outlives obligations from the later.
+        let vis = if is_root_goal {


why special-case root goals here?

View changes since the review

I thought that we should only ignore region constraints from nested goals and if I mark them as VisibleForLeakCheck::No for root goals as well, they would be so in the InferCtxt outside of the solver and then ignored from the leak check for other goals as well, but after thinking twice, they wouldn't cause universe leaks in other goals anyway 😅 Yeah, so might be okay to remove the spacial casing here

lcnr · 2026-04-30T07:24:24Z

            .into_iter()
-            .filter(|&(outlives, _)| seen.insert(outlives))
-            .map(|(outlives, _)| outlives)
+            .filter(|&(outlives, _, vis)| seen.insert((outlives, vis)))


this may cause us to end up with the same constraint with vis: Yes and vis: No 🤔 I guess it's fine as long as that doesn't cause issues

View changes since the review

I did this deliberately as we could already have the same constraints with different visibilities without this and if that would be the case, the resulting visibility would be order-dependent 🤔

could eagerly collect into a list, and use a hashmap pointing to the index of the element, on a hit we Or the visibility

lcnr · 2026-04-30T07:27:25Z

                            t1,
                            r2,
                            constraint_category,
+                            ty::VisibleForLeakCheck::Yes,


slightly concerning 🤔

how hard is it to pass VisibleForLeakCheck to here?

View changes since the review

I guess it wouldn't be that hard but I thought visibilities are not real concerns here in borrowck

they are not 😅 I would love us to somehow defensively guard against this... as rn u need to globally reason about this code for whether it's correct

what do you think you make it into a three-state enum with Yes, No, Unreachable and have the leak_check ICE when encountering Unreachable

Ah, yes, such global context would be very confusing and fragile to future changes 😅 That would be more desirable 👍

lcnr · 2026-04-30T07:28:49Z

        ty: Ty<'tcx>,
        region: ty::Region<'tcx>,
        category: ConstraintCategory<'tcx>,
+        vis: ty::VisibleForLeakCheck,


components_must_outlive can always be ty::VisibleForLeakcheck::No/ for TypeOutlives in general 🤔

View changes since the review

I guess they might be decomposed into RegionOutlivesPredicate with component-wise thingy. Would it be okay?

it matches the old solver which currently never considers type outlives in the leak check 🤔

but also, we only ever use this in places which won't ever leak check anymore, so 🤷

Maybe we could try VisibleForLeakCheck::Unreachable here as well?

rustbot · 2026-04-30T15:48:17Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

lcnr · 2026-05-01T07:20:53Z

        _constraint_category: ConstraintCategory<'tcx>,
    ) {
-        self.sub_regions(origin, a, b)
+        // We don't do leak check in borrowck


That one is for lexical region resolution, not borrowck afaik

View changes since the review

There were one occurence of this in borrowck while I was working on but it became non-neceessary after that, but I was confused by thinking something like "hmm, there were one of these in borrowck" 😅

yes, this is the implementation used outside of borrowck ,borrowck has a separate impl :3

lcnr · 2026-05-01T07:22:50Z

+        let mut constraints = vec![];
+        let mut visibilities = vec![];


why two Vec instead of storing it as a tuple right away and returning that one

View changes since the review

lcnr · 2026-05-01T07:23:55Z

+            (VisibleForLeakCheck::Unreachable, VisibleForLeakCheck::Unreachable) => {
+                VisibleForLeakCheck::Unreachable
+            }


I would have Unreachable overwrite Yes because it acts more like an Option<VisibleForLeakCheck> 🤔

View changes since the review

lcnr · 2026-05-01T07:24:12Z

@@ -0,0 +1,43 @@
+//@ check-pass
+//@ compile-flags: -Znext-solver=globally


can you use revisions in these tests?

View changes since the review

lcnr

surprising that this doesn't break any of our coherence tests 🤔 😅

View changes since this review

ShoyuVanilla · 2026-05-01T10:58:33Z

surprising that this doesn't break any of our coherence tests 🤔 😅

Yeah, the initial draft for this couldn't even compile std due to coherence errors as it couldn't filter out the candidates that should fail the leak checks, but after some edits, everything just began to work as is 🤔

lcnr · 2026-05-01T13:05:04Z

+impl VisibleForLeakCheck {
+    pub fn and(self, other: VisibleForLeakCheck) -> VisibleForLeakCheck {
+        match (self, other) {
+            // Make sure that we never overwrite the constraints shouldn't be leak checked


Suggested change

// Make sure that we never overwrite the constraints shouldn't be leak checked

// Make sure that we never overwrite that constraints shouldn't

// be encountered by the leak checked

View changes since the review

lcnr · 2026-05-01T13:05:13Z

+
+    pub fn or(self, other: VisibleForLeakCheck) -> VisibleForLeakCheck {
+        match (self, other) {
+            // Make sure that we never overwrite the constraints shouldn't be leak checked


Suggested change

// Make sure that we never overwrite the constraints shouldn't be leak checked

// Make sure that we never overwrite that constraints shouldn't

// be encountered by the leak checked

View changes since the review

lcnr · 2026-05-01T13:05:46Z

+// This previously caused an ICE due to a non–well-formed coroutine
+// hidden type failing the leak check in the next-solver.


Suggested change

// This previously caused an ICE due to a non–well-formed coroutine

// hidden type failing the leak check in the next-solver.

// This previously caused an ICE due to a non–well-formed opaque type

// in a coroutine witness failing the leak check in the next-solver.

View changes since the review

lcnr · 2026-05-01T13:06:23Z

+// This previously caused an ICE due to a non–well-formed coroutine
+// hidden type failing the leak check in the next-solver.


you have either

coroutine witness type

or opaque type hidden type

coroutines don't have hidden types :>

View changes since the review

lcnr · 2026-05-01T13:06:38Z

+// Regression test for <https://github.com/rust-lang/trait-system-refactor-initiative/issues/251>.
+//
+// This previously caused an ICE due to a non–well-formed coroutine
+// hidden type failing the leak check in the next-solver.


same here

View changes since the review

lcnr

final nits, then r=me

View changes since this review

…akcheck

ShoyuVanilla · 2026-05-01T21:49:44Z

@bors r=lcnr

rust-bors · 2026-05-01T21:49:46Z

📌 Commit e43a1b5 has been approved by lcnr

It is now in the queue for this repository.

Rollup of 4 pull requests Successful merges: - #154571 (Fix alias path for rustdoc) - #155749 (`-Znext-solver` Ignore region constraints from the nested goals in leakcheck) - #156026 (`bufreader::Buffer`: Remove leftover note about `initialized` field) - #156063 (Map `WSAESHUTDOWN` to `io::ErrorKind::BrokenPipe`)

Rollup merge of #155749 - ShoyuVanilla:leakcheck-vis, r=lcnr `-Znext-solver` Ignore region constraints from the nested goals in leakcheck Fixes rust-lang/trait-system-refactor-initiative#251 Fixes #140577 Fixes #153596

ShoyuVanilla changed the title ~~-Znext-solver Ignore region constraints from the nested goals in leakcheck~~ -Znext-solver Ignore region constraints from the nested goals in leakcheck Apr 24, 2026

ShoyuVanilla force-pushed the leakcheck-vis branch from 589add8 to e4719c4 Compare April 25, 2026 02:50

ShoyuVanilla mentioned this pull request Apr 25, 2026

Canonicalize free regions from inputs as placeholders in root univ #155487

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ShoyuVanilla force-pushed the leakcheck-vis branch 2 times, most recently from e2650aa to 54588cf Compare April 27, 2026 16:23

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ShoyuVanilla force-pushed the leakcheck-vis branch from 54588cf to 29dab0f Compare April 30, 2026 03:22

rustbot assigned lcnr Apr 30, 2026

ShoyuVanilla marked this pull request as ready for review April 30, 2026 03:23

rustbot 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 Apr 30, 2026

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ShoyuVanilla force-pushed the leakcheck-vis branch from 29dab0f to cff8c42 Compare April 30, 2026 15:48

ShoyuVanilla force-pushed the leakcheck-vis branch from cff8c42 to 7be9fb6 Compare April 30, 2026 17:49

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ShoyuVanilla force-pushed the leakcheck-vis branch from 7be9fb6 to 961abdd Compare May 1, 2026 10:56

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-Znext-solver Ignore region constraints from the nested goals in le…

e43a1b5

…akcheck

ShoyuVanilla force-pushed the leakcheck-vis branch from 961abdd to e43a1b5 Compare May 1, 2026 15:11

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 May 1, 2026

GuillaumeGomez mentioned this pull request May 2, 2026

Rollup of 4 pull requests #156072

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rust-bors Bot merged commit e95df7d into rust-lang:main May 2, 2026
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rustbot added this to the 1.97.0 milestone May 2, 2026

lcnr mentioned this pull request May 5, 2026

Fix vtable ICE on unsatisfied supertrait bounds #154129

Open

-                                each_edge(sub, sup, visible_for_leak_check)
+                                match visible_for_leak_check {
+                                    ty::VisibleForLeakCheck::Yes =>
+                                each_edge(sub, sup),
+                                    ty::VisibleForLeakCheck::No => {}
+                                }

		pub type QueryRegionConstraint<'tcx> =
		(ty::RegionConstraint<'tcx>, ConstraintCategory<'tcx>, ty::VisibleForLeakCheck);

		@@ -0,0 +1,43 @@
		//@ check-pass
		//@ compile-flags: -Znext-solver=globally

	// Make sure that we never overwrite the constraints shouldn't be leak checked
	// Make sure that we never overwrite that constraints shouldn't
	// be encountered by the leak checked

		// This previously caused an ICE due to a non–well-formed coroutine
		// hidden type failing the leak check in the next-solver.

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