Rollup merge of #37708 - oli-obk:box_free, r=eddyb

change the `box_free` lang item to accept pointers to unsized types

in miri we use the `box_free` lang item as the destructor for `Box` objects, since the function's api matches that of an `fn drop(&mut self)` in a hypothetical `impl<T: ?Sized> Drop for Box<T>` exactly.

This works fine except if we insert a check in the `size_of` intrinsic to ensure that it is only called with sized types, since the `box_free` lang item calls that intrinsic.

cc @eddyb

no clue who to r? here, probably lang team?

1 files changed, 2 insertions, 2 deletions

diff --git a/src/doc/book/lang-items.md b/src/doc/book/lang-items.md
index de7dbab3f12..9fb130845fb 100644
--- a/src/doc/book/lang-items.md
+++ b/src/doc/book/lang-items.md
@@ -46,8 +46,8 @@ unsafe fn deallocate(ptr: *mut u8, _size: usize, _align: usize) {
 }
 
 #[lang = "box_free"]
-unsafe fn box_free<T>(ptr: *mut T) {
-    deallocate(ptr as *mut u8, ::core::mem::size_of::<T>(), ::core::mem::align_of::<T>());
+unsafe fn box_free<T: ?Sized>(ptr: *mut T) {
+    deallocate(ptr as *mut u8, ::core::mem::size_of_val(&*ptr), ::core::mem::align_of_val(&*ptr));
 }
 
 #[start]