fix: unnecessary_to_owned FP when map key is a reference

Author: profetia

clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -739,6 +739,10 @@ fn check_borrow_predicate<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
         && let caller_ty = cx.typeck_results().expr_ty(caller)
         // For now we limit it to "map types".
         && is_a_std_map_type(cx, caller_ty)
+        // We need to check that the key type is not a reference.
+        && let ty::Adt(_, caller_ty_args) = caller_ty.kind()
+        && let (_, n_key_ref) = peel_middle_ty_refs(caller_ty_args.type_at(0))
+        && n_key_ref == 0
     {
         check_if_applicable_to_argument(cx, &arg);
     }

tests/ui/unnecessary_to_owned.fixed

@@ -675,3 +675,9 @@ mod issue_14242 {
         rc_slice_provider().to_vec().into_iter()
     }
 }
+
+fn issue14833() {
+    use std::collections::HashSet;
+    let mut s = HashSet::<&String>::new();
+    s.remove(&"hello".to_owned());
+}

tests/ui/unnecessary_to_owned.rs

@@ -675,3 +675,9 @@ mod issue_14242 {
         rc_slice_provider().to_vec().into_iter()
     }
 }
+
+fn issue14833() {
+    use std::collections::HashSet;
+    let mut s = HashSet::<&String>::new();
+    s.remove(&"hello".to_owned());
+}