Add UI test for issue 74933

src/test/ui/typeck/issue-74933.rs

@@ -0,0 +1,38 @@
+// check-pass
+//
+// rust-lang/rust#74933: Lifetime error when indexing with borrowed index
+
+use std::ops::{Index, IndexMut};
+
+struct S(V);
+struct K<'a>(&'a ());
+struct V;
+
+impl<'a> Index<&'a K<'a>> for S {
+    type Output = V;
+
+    fn index(&self, _: &'a K<'a>) -> &V {
+        &self.0
+    }
+}
+
+impl<'a> IndexMut<&'a K<'a>> for S {
+    fn index_mut(&mut self, _: &'a K<'a>) -> &mut V {
+        &mut self.0
+    }
+}
+
+impl V {
+    fn foo(&mut self) {}
+}
+
+fn test(s: &mut S, k: &K<'_>) {
+    s[k] = V;
+    s[k].foo();
+}
+
+fn main() {
+    let mut s = S(V);
+    let k = K(&());
+    test(&mut s, &k);
+}