Function cst_node_as 

pub unsafe fn cst_node_as<T>(node: *mut CstNode) -> *mut T
where
    T: CstNodeClass,

cstNode->as<T>() — downcast a base *mut CstNode to *mut T, or null on mismatch.

Safety

node must be null or point to a live CST node whose first field is (transitively) a CstNode — i.e. any generated #[repr(C)] CST node struct.