don't call iter() on a temporary object in unnecessary_to_owned

clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -219,6 +219,8 @@ fn check_into_iter_call_arg(
         && let Some(receiver_snippet) = receiver.span.get_source_text(cx)
         // If the receiver is a `Cow`, we can't remove the `into_owned` generally, see https://github.com/rust-lang/rust-clippy/issues/13624.
         && !is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::Cow)
+        // Calling `iter()` on a temporary object can lead to false positives. #14242
+        && !matches!(receiver.kind, ExprKind::Call(..) | ExprKind::Struct(..) | ExprKind::Tup(..))
     {
         if unnecessary_iter_cloned::check_for_loop_iter(cx, parent, method_name, receiver, true) {
             return true;

tests/ui/unnecessary_to_owned.fixed

@@ -679,3 +679,18 @@ fn issue13624() -> impl IntoIterator {
 
     cow.into_owned().into_iter()
 }
+
+mod issue_14242 {
+    use std::rc::Rc;
+
+    #[derive(Copy, Clone)]
+    struct Foo;
+
+    fn rc_slice_provider() -> Rc<[Foo]> {
+        Rc::from([Foo])
+    }
+
+    fn iterator_provider() -> impl Iterator<Item = Foo> {
+        rc_slice_provider().to_vec().into_iter()
+    }
+}

tests/ui/unnecessary_to_owned.rs

@@ -679,3 +679,18 @@ fn issue13624() -> impl IntoIterator {
 
     cow.into_owned().into_iter()
 }
+
+mod issue_14242 {
+    use std::rc::Rc;
+
+    #[derive(Copy, Clone)]
+    struct Foo;
+
+    fn rc_slice_provider() -> Rc<[Foo]> {
+        Rc::from([Foo])
+    }
+
+    fn iterator_provider() -> impl Iterator<Item = Foo> {
+        rc_slice_provider().to_vec().into_iter()
+    }
+}