2 files changed, 54 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui-toml/mut_key/clippy.toml b/src/tools/clippy/tests/ui-toml/mut_key/clippy.toml
new file mode 100644
index 000000000..6d33e192e
--- /dev/null
+++ b/src/tools/clippy/tests/ui-toml/mut_key/clippy.toml
@@ -0,0 +1 @@
+ignore-interior-mutability = ["mut_key::Counted"]
+\ No newline at end of file
diff --git a/src/tools/clippy/tests/ui-toml/mut_key/mut_key.rs b/src/tools/clippy/tests/ui-toml/mut_key/mut_key.rs
new file mode 100644
index 000000000..667c51cb4
--- /dev/null
+++ b/src/tools/clippy/tests/ui-toml/mut_key/mut_key.rs
@@ -0,0 +1,53 @@
+// compile-flags: --crate-name mut_key
+
+#![warn(clippy::mutable_key_type)]
+
+use std::cmp::{Eq, PartialEq};
+use std::collections::{HashMap, HashSet};
+use std::hash::{Hash, Hasher};
+use std::ops::Deref;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+struct Counted<T> {
+    count: AtomicUsize,
+    val: T,
+}
+
+impl<T: Clone> Clone for Counted<T> {
+    fn clone(&self) -> Self {
+        Self {
+            count: AtomicUsize::new(0),
+            val: self.val.clone(),
+        }
+    }
+}
+
+impl<T: PartialEq> PartialEq for Counted<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.val == other.val
+    }
+}
+impl<T: PartialEq + Eq> Eq for Counted<T> {}
+
+impl<T: Hash> Hash for Counted<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.val.hash(state);
+    }
+}
+
+impl<T> Deref for Counted<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        self.count.fetch_add(1, Ordering::AcqRel);
+        &self.val
+    }
+}
+
+// This is not linted because `"mut_key::Counted"` is in
+// `arc_like_types` in `clippy.toml`
+fn should_not_take_this_arg(_v: HashSet<Counted<String>>) {}
+
+fn main() {
+    should_not_take_this_arg(HashSet::new());
+}