Auto merge of #64938 - estebank:ice-ice-baby, r=matthewjasper

Avoid ICE on ReFree region on where clause

Fix #64855.

4 files changed, 29 insertions, 2 deletions

diff --git a/src/librustc_typeck/outlives/utils.rs b/src/librustc_typeck/outlives/utils.rs
index d83c97b522c..d34605dc482 100644
--- a/src/librustc_typeck/outlives/utils.rs
+++ b/src/librustc_typeck/outlives/utils.rs
@@ -161,9 +161,14 @@ fn is_free_region(tcx: TyCtxt<'_>, region: Region<'_>) -> bool {
         // ignore it.  We can't put it on the struct header anyway.
         RegionKind::ReLateBound(..) => false,
 
+        // This can appear in `where Self: ` bounds (#64855):
+        //
+        //     struct Bar<T>(<Self as Foo>::Type) where Self: ;
+        //     struct Baz<'a>(&'a Self) where Self: ;
+        RegionKind::ReEmpty => false,
+
         // These regions don't appear in types from type declarations:
-        RegionKind::ReEmpty
-        | RegionKind::ReErased
+        RegionKind::ReErased
         | RegionKind::ReClosureBound(..)
         | RegionKind::ReScope(..)
         | RegionKind::ReVar(..)
diff --git a/src/test/ui/associated-types/issue-64855-2.rs b/src/test/ui/associated-types/issue-64855-2.rs
new file mode 100644
index 00000000000..1d53bd57031
--- /dev/null
+++ b/src/test/ui/associated-types/issue-64855-2.rs
@@ -0,0 +1,5 @@
+// check-pass
+
+pub struct Bar<'a>(&'a Self) where Self: ;
+
+fn main() {}
diff --git a/src/test/ui/associated-types/issue-64855.rs b/src/test/ui/associated-types/issue-64855.rs
new file mode 100644
index 00000000000..81cf3ae6e83
--- /dev/null
+++ b/src/test/ui/associated-types/issue-64855.rs
@@ -0,0 +1,8 @@
+pub trait Foo {
+    type Type;
+}
+
+pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
+//~^ ERROR the trait bound `Bar<T>: Foo` is not satisfied
+
+fn main() {}
diff --git a/src/test/ui/associated-types/issue-64855.stderr b/src/test/ui/associated-types/issue-64855.stderr
new file mode 100644
index 00000000000..6ad795c1117
--- /dev/null
+++ b/src/test/ui/associated-types/issue-64855.stderr
@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `Bar<T>: Foo` is not satisfied
+  --> $DIR/issue-64855.rs:5:19
+   |
+LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
+   |                   ^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `Bar<T>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.