Unable to get nested mut VTag from mut VList

[XX]

I have the extension methods for VTag like this:

fn find_child_contains_class_mut(&mut self, class: &str) -> Option<&mut VTag>;
fn find_child_contains_class_recursively_mut(&mut self, class: &str) -> Option<&mut VTag>;

They were broken after using ChildrenMut as return type of the VList::children_mut: #2673. Now I have lost the ability to use these methods in API of my libs. ((

How to fix it?

[WorldSEnder]

ChildrenMut has a DerefMut implementation to Vec<VNode> that you can use to access the nodes of the list directly. Is there any problem you're facing with that approach?

[XX]

@WorldSEnder The problem is that the ChildrenMut object is dropped at the end of the method, so it's impossible to return the VTag reference. And for the recursive search, it's impossible to return the final ChildrenMut object also.

[WorldSEnder]

Right, that problem is akin to only getting Ref from a RefCell when borrowing, because it has to restore some internal invariants when unborrowing. In our case, the invariant it re-checks is fully_keyed, which solves the problem in #2654 (no manual check needed any longer).

I see a potential solution: delay checking fully_keyed for vlists that get borrowed mutably until they get mounted.

2 small concerns about that, for completeness, I still think it's a good solution:

• traverses a potentially long list at mount time, and the performance hit is hard to track back to where the VList was constructed.
• need to ensure that known-good lists from the macro still optimize with a compile time computed fully_keyed