Fix ICE in borrowck when recovering `fn_sig` for `-> _` by JohnTitor · Pull Request #152323 · rust-lang/rust

JohnTitor · 2026-02-08T07:47:26Z

(Should be) a proper fix for #135845, replaces a dummy binder with a concrete one not to ICE, as mentioned in #147631 (comment).
Fixes #135845
r? @lcnr @jackh726

lcnr · 2026-02-11T15:30:02Z

compiler/rustc_hir_analysis/src/collect.rs

+    );
+
+    let fn_sig = fold_regions(tcx, fn_sig, |r, _| match r.kind() {
+        ty::ReLateParam(lp) if lp.scope == scope => {


this if should be an assert, should it not?

Ah right, it's inconsistency and should be rejected.

Addressed in: 313959d

lcnr · 2026-02-11T15:30:12Z

compiler/rustc_hir_analysis/src/collect.rs

+                }
+            };
+
+            br.map(|br| ty::Region::new_bound(tcx, ty::INNERMOST, br))


ty::INNERMOST is wrong, u need to use the binder from the closure argument.

Also, can you move this into a utility function fn late_param_regions_to_bound or sth like this. I think this code is too general (and somewhat subtle to understand) for it to be inline here

also, we should be able to just unwrap here 🤔 having spurious late bound regions is a compiler bug

Extracted and used debruijn instead: 313959d

lcnr · 2026-02-12T12:00:45Z

compiler/rustc_hir_analysis/src/collect.rs

+    scope: DefId,
+    bound_vars: &'tcx ty::List<ty::BoundVariableKind<'tcx>>,
+    value: T,
+) -> T


return a Binder instead of doing so in the caller :3

lcnr

thanks 😊

r=me after nit

View changes since this review

rustbot · 2026-02-13T07:50:10Z

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.

JohnTitor · 2026-02-13T07:50:51Z

Thank you for the review, too!
@bors r=lcnr

rust-bors · 2026-02-13T07:50:54Z

📌 Commit b0f2ac8 has been approved by lcnr

It is now in the queue for this repository.

@lcnr

Fix ICE in borrowck when recovering `fn_sig` for `-> _` (Should be) a proper fix for rust-lang#135845, replaces a dummy binder with a concrete one not to ICE, as mentioned in rust-lang#147631 (comment). Fixes rust-lang#135845 r? @lcnr @jackh726

@lcnr

Fix ICE in borrowck when recovering `fn_sig` for `-> _` (Should be) a proper fix for rust-lang#135845, replaces a dummy binder with a concrete one not to ICE, as mentioned in rust-lang#147631 (comment). Fixes rust-lang#135845 r? @lcnr @jackh726

@lcnr

Fix ICE in borrowck when recovering `fn_sig` for `-> _` (Should be) a proper fix for rust-lang#135845, replaces a dummy binder with a concrete one not to ICE, as mentioned in rust-lang#147631 (comment). Fixes rust-lang#135845 r? @lcnr @jackh726

…uwer Rollup of 14 pull requests Successful merges: - #152323 (Fix ICE in borrowck when recovering `fn_sig` for `-> _`) - #152469 (Remove unused features) - #152515 (Extract `DepKindVTable` constructors to their own module) - #152555 (Port `#[rustc_diagnostic_item]` to the new attribute parsers) - #152218 (Report unconstrained region in hidden types lazily) - #152356 (Improve the `inline_fluent!` macro) - #152392 (Fix ICE in supertrait_vtable_slot when supertrait has missing generics) - #152407 (Add regression test for type_const with unit struct ctor under mGCA) - #152440 (Fix typos and grammar in compiler and build documentation) - #152536 (bootstrap: add explicit UTF-8 encoding to text-mode open() calls) - #152554 (Remove `deprecated_safe` and its corresponding feature gate) - #152556 (doc: move riscv64a23-unknown-linux-gnu to tier 2) - #152563 (Replace "bug" with "issue" in triagebot ping messages) - #152565 (fix missleading error for tuple ctor) Failed merges: - #152512 (core: Implement feature `float_exact_integer_constants`) - #152296 (Port `rust_nonnull_optimization_guaranteed` and `rustc_do_not_const_check` to the new attribute parser)

@lcnr

Rollup merge of #152323 - JohnTitor:issue-135845-2, r=lcnr Fix ICE in borrowck when recovering `fn_sig` for `-> _` (Should be) a proper fix for #135845, replaces a dummy binder with a concrete one not to ICE, as mentioned in #147631 (comment). Fixes #135845 r? @lcnr @jackh726

rustbot assigned lcnr Feb 8, 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 Feb 8, 2026

lcnr reviewed Feb 11, 2026

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JohnTitor force-pushed the issue-135845-2 branch from c5a55e8 to 313959d Compare February 12, 2026 11:16

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JohnTitor added 3 commits February 13, 2026 12:26

Fix ICE in borrowck when recovering fn_sig for -> _

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JohnTitor force-pushed the issue-135845-2 branch from 313959d to b0f2ac8 Compare February 13, 2026 07:50

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 Feb 13, 2026

JonathanBrouwer mentioned this pull request Feb 13, 2026

Rollup of 14 pull requests #152571

Closed

This was referenced Feb 13, 2026

Rollup of 14 pull requests #152572

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Rollup of 14 pull requests #152574

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rust-bors bot merged commit 9d662b5 into rust-lang:main Feb 14, 2026
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rustbot added this to the 1.95.0 milestone Feb 14, 2026

JohnTitor deleted the issue-135845-2 branch February 14, 2026 03:21

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Fix ICE in borrowck when recovering `fn_sig` for `-> _`#152323

Fix ICE in borrowck when recovering `fn_sig` for `-> _`#152323
rust-bors[bot] merged 3 commits intorust-lang:mainfrom
JohnTitor:issue-135845-2

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