add regression test for ICE unexpected region

tests/ui/associated-consts/assoc-const-equality-unexpected-region.rs

@@ -0,0 +1,14 @@
+//! Regression test for https://github.com/rust-lang/rust/issues/143896.
+
+trait TraitA<'a> {
+    const K: usize = 0;
+}
+
+impl<T> TraitA<'_> for () {}
+//~^ ERROR the type parameter `T` is not constrained
+
+impl dyn TraitA<'_> where (): TraitA<'a, K = 0> {}
+//~^ ERROR use of undeclared lifetime name `'a`
+//~| ERROR associated const equality is incomplete
+
+pub fn main() {}

tests/ui/associated-consts/assoc-const-equality-unexpected-region.stderr

@@ -0,0 +1,40 @@
+error[E0261]: use of undeclared lifetime name `'a`
+  --> $DIR/assoc-const-equality-unexpected-region.rs:10:38
+   |
+LL | impl dyn TraitA<'_> where (): TraitA<'a, K = 0> {}
+   |                                      ^^ undeclared lifetime
+   |
+   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
+help: consider making the bound lifetime-generic with a new `'a` lifetime
+   |
+LL | impl dyn TraitA<'_> where (): for<'a> TraitA<'a, K = 0> {}
+   |                               +++++++
+help: consider making the bound lifetime-generic with a new `'a` lifetime
+   |
+LL | impl dyn TraitA<'_> where for<'a> (): TraitA<'a, K = 0> {}
+   |                           +++++++
+help: consider introducing lifetime `'a` here
+   |
+LL | impl<'a> dyn TraitA<'_> where (): TraitA<'a, K = 0> {}
+   |     ++++
+
+error[E0658]: associated const equality is incomplete
+  --> $DIR/assoc-const-equality-unexpected-region.rs:10:42
+   |
+LL | impl dyn TraitA<'_> where (): TraitA<'a, K = 0> {}
+   |                                          ^^^^^
+   |
+   = note: see issue #132980 <https://github.com/rust-lang/rust/issues/132980> for more information
+   = help: add `#![feature(min_generic_const_args)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/assoc-const-equality-unexpected-region.rs:7:6
+   |
+LL | impl<T> TraitA<'_> for () {}
+   |      ^ unconstrained type parameter
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0207, E0261, E0658.
+For more information about an error, try `rustc --explain E0207`.