Do not recurse indefinitely while checking for inner mutability

`clippy_utils::ty::InteriorMut::interior_mut_ty_chain` must stop
recursing forever when types are chained indefinitely due to the use of
associated types in generics. A false negative is acceptable, and
documented here.

Should this situation be later identified specifically, a conversion of
`Option` to `Result` would allow separating the infinitely recursive
case from a negative one.

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/ui/crashes/ice-14935.rs b/tests/ui/crashes/ice-14935.rs
new file mode 100644
index 00000000000..74cda9aae53
--- /dev/null
+++ b/tests/ui/crashes/ice-14935.rs
@@ -0,0 +1,27 @@
+//@check-pass
+#![warn(clippy::mutable_key_type)]
+
+use std::marker::PhantomData;
+
+trait Group {
+    type ExposantSet: Group;
+}
+
+struct Pow<T: Group> {
+    exposant: Box<Pow<T::ExposantSet>>,
+    _p: PhantomData<T>,
+}
+
+impl<T: Group> Pow<T> {
+    fn is_zero(&self) -> bool {
+        false
+    }
+    fn normalize(&self) {
+        #[expect(clippy::if_same_then_else)]
+        if self.is_zero() {
+        } else if false {
+        }
+    }
+}
+
+fn main() {}