Everywhere: Prevent risky implicit casts of (Nonnull)RefPtr

Our existing implementation did not check the element type of the other
pointer in the constructors and move assignment operators. This meant
that some operations that would require explicit casting on raw pointers
were done implicitly, such as:
- downcasting a base class to a derived class (e.g. `Kernel::Inode` =>
  `Kernel::ProcFSDirectoryInode` in Kernel/ProcFS.cpp),
- casting to an unrelated type (e.g. `Promise<bool>` => `Promise<Empty>`
  in LibIMAP/Client.cpp)

This, of course, allows gross violations of the type system, and makes
the need to type-check less obvious before downcasting. Luckily, while
adding the `static_ptr_cast`s, only two truly incorrect usages were
found; in the other instances, our casts just needed to be made
explicit.

1 files changed, 1 insertions, 1 deletions

diff --git a/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp b/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp
index 74b52e9b41..955416f9a9 100644
--- a/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp
+++ b/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp
@@ -166,7 +166,7 @@ void TreeBuilder::remove_irrelevant_boxes(NodeWithStyle& root)
 {
     // The following boxes are discarded as if they were display:none:
 
-    NonnullRefPtrVector<Box> to_remove;
+    NonnullRefPtrVector<Node> to_remove;
 
     // Children of a table-column.
     for_each_in_tree_with_display<CSS::Display::TableColumn>(root, [&](Box& table_column) {