We could prevent the possibility of any future memory leaks by:

• Introduce a trait Arena.
• Implement it for:
  • all primitive types which do not own external allocations - u32, &str etc.
  • oxc_allocator's Box, Vec and String.
• Create a derive macro for the trait which requires all struct fields / enum variants to also be Arena (same as a type can only be Clone if all its constituent parts are also Clone).
• #[derive(Arena)] on all AST types.
• Add a bound to Allocator::alloc<T: Arena>.

The compiler will then make it impossible to add any type which owns data external to the arena to the AST, or allocate one in the arena.