fix crashes

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -2230,7 +2230,7 @@ impl<'tcx> RegionDefinition<'tcx> {
     fn new(universe: ty::UniverseIndex, rv_origin: RegionVariableOrigin) -> Self {
         // Create a new region definition. Note that, for free
         // regions, the `external_name` field gets updated later in
-        // `init_universal_regions`.
+        // `init_free_and_bound_regions`.
 
         let origin = match rv_origin {
             RegionVariableOrigin::Nll(origin) => origin,

tests/crashes/124021.rs

@@ -1,6 +0,0 @@
-//@ known-bug: #124021
-type Opaque2<'a> = impl Sized + 'a;
-
-fn test2() -> impl for<'a, 'b> Fn((&'a str, &'b str)) -> (Opaque2<'a>, Opaque2<'a>) {
-    |x| x
-}

tests/ui/borrowck/overwrite-anon-late-param-regions.rs

@@ -0,0 +1,15 @@
+// A regression test for #124021. When liberating the late bound regions here
+// we encounter multiple `LateBoundRegion::Anon`. These ended up resulting in
+// distinct nll vars, but mapped to the same `RegionKind::LateParam`. This
+// then caused an ICE when trying to fetch lazily computed information for the
+// nll var of an overwritten liberated bound region.
+#![feature(type_alias_impl_trait)]
+type Opaque2<'a> = impl Sized + 'a;
+
+fn test2() -> impl for<'a, 'b> Fn((&'a str, &'b str)) -> (Opaque2<'a>, Opaque2<'a>) {
+    |x| x
+    //~^ ERROR lifetime may not live long enough
+    //~| ERROR expected generic lifetime parameter, found `'a`
+}
+
+fn main() {}

tests/ui/borrowck/overwrite-anon-late-param-regions.stderr

@@ -0,0 +1,21 @@
+error: lifetime may not live long enough
+  --> $DIR/overwrite-anon-late-param-regions.rs:10:9
+   |
+LL |     |x| x
+   |      -  ^ closure was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
+   |      |
+   |      has type `(&str, &'1 str)`
+   |      has type `(&'2 str, &str)`
+
+error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/overwrite-anon-late-param-regions.rs:10:5
+   |
+LL | type Opaque2<'a> = impl Sized + 'a;
+   |              -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |     |x| x
+   |     ^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0792`.