Code change:
<!-- [31mICE[0m: Rustc '' 'thread 'rustc' panicked at 'expected region for ('a//0) but found Type(&'{erased} mut FooImpl<'{erased}, '{erased}, T/) when instantiating args=[&'{erased} mut FooImpl<'{erased}, '{erased}, T/, '?27, ?2t, Closure(DefId(0:22 ~ a[a197]::{impl}::foo::{closure}), ['{erased}, '{erased}, T/, i32, Binder(fn((&ReLateParam(DefId(0:22 ~ a[a197]::{impl}::foo::{closure}), BrAnon) mut FooImpl<'{erased}, '{erased}, T/,)), []), ()])]'', 'thread 'rustc' panicked at 'expected region for ('a//0) but found Type(&'{erased} mut FooImpl<'{erased}, '{erased}, T/) when instantiating args=[&'{erased} mut FooImpl<'{erased}, '{erased}, T/, '?27, ?2t, Closure(DefId(0:22 ~ a[a197]::{impl}::foo::{closure}), ['{erased}, '{erased}, T/, i32, Binder(fn((&ReLateParam(DefId(0:22 ~ a[a197]::{impl}::foo::{closure}), BrAnon) mut FooImpl<'{erased}, '{erased}, T/,)), []), ()])]'' File: --auto-reduced (treereduce-rust): original: Version information ` Command: <!-- Include a backtrace in the code block by setting in your environment. E.g. . --<details<summary<strongProgram output</strong</summary<p</p</details<!-- query stack: [mirborrowck] borrow-checking [mirborrowck] borrow-checking --
ICEs on nightly and beta, but not on stable. Minimized further: <details<summaryProgram output</summary</details
The ICE is another one from , cc
Still reproduces on 1.81.0-nightly (2024-06-13 ) -E-needs-test
I'll look into it later today.

Related discussion:
text: <ins> error[E0478]: lifetime bound not satisfied --> $DIR/lifetime-not-long-enough-suggestion-regression-test-124563.rs:19:16 | LL |     type Bar = BarImpl<'a, 'b, T>; |                ^^^^^^^^^^^^^^^^^^ | note: lifetime parameter instantiated with the lifetime `'a` as defined here --> $DIR/lifetime-not-long-enough-suggestion-regression-test-124563.rs:14:6 | LL | impl<'a, 'b, T> Foo for FooImpl<'a, 'b, T> |      ^^ note: but lifetime parameter must outlive the lifetime `'b` as defined here --> $DIR/lifetime-not-long-enough-suggestion-regression-test-124563.rs:14:10 | LL | impl<'a, 'b, T> Foo for FooImpl<'a, 'b, T> |          ^^ error: lifetime may not live long enough --> $DIR/lifetime-not-long-enough-suggestion-regression-test-124563.rs:23:21 | LL |         self.enter_scope(|ctx| { |                           --- |                           | |                           has type `&'1 mut FooImpl<'_, '_, T>` |                           has type `&mut FooImpl<'2, '_, T>` LL |             BarImpl(ctx); |                     ^^^ this usage requires that `'1` must outlive `'2` error: lifetime may not live long enough --> $DIR/lifetime-not-long-enough-suggestion-regression-test-124563.rs:22:9 | LL |   impl<'a, 'b, T> Foo for FooImpl<'a, 'b, T> |        --  -- lifetime `'b` defined here |        | |        lifetime `'a` defined here ... LL | /         self.enter_scope(|ctx| { LL | |             BarImpl(ctx); LL | |         }); | |__________^ argument requires that `'a` must outlive `'b` | = help: consider adding the following bound: `'a: 'b` = note: requirement occurs because of a mutable reference to `FooImpl<'_, '_, T>` = note: mutable references are invariant over their type parameter = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0478`. </ins>