Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 855 insertions, 0 deletions

diff --git a/library/core/tests/ptr.rs b/library/core/tests/ptr.rs
new file mode 100644
index 000000000..12861794c
--- /dev/null
+++ b/library/core/tests/ptr.rs
@@ -0,0 +1,855 @@
+use core::cell::RefCell;
+use core::mem::{self, MaybeUninit};
+use core::num::NonZeroUsize;
+use core::ptr;
+use core::ptr::*;
+use std::fmt::{Debug, Display};
+
+#[test]
+fn test_const_from_raw_parts() {
+    const SLICE: &[u8] = &[1, 2, 3, 4];
+    const FROM_RAW: &[u8] = unsafe { &*slice_from_raw_parts(SLICE.as_ptr(), SLICE.len()) };
+    assert_eq!(SLICE, FROM_RAW);
+
+    let slice = &[1, 2, 3, 4, 5];
+    let from_raw = unsafe { &*slice_from_raw_parts(slice.as_ptr(), 2) };
+    assert_eq!(&slice[..2], from_raw);
+}
+
+#[test]
+fn test() {
+    unsafe {
+        #[repr(C)]
+        struct Pair {
+            fst: isize,
+            snd: isize,
+        }
+        let mut p = Pair { fst: 10, snd: 20 };
+        let pptr: *mut Pair = &mut p;
+        let iptr: *mut isize = pptr as *mut isize;
+        assert_eq!(*iptr, 10);
+        *iptr = 30;
+        assert_eq!(*iptr, 30);
+        assert_eq!(p.fst, 30);
+
+        *pptr = Pair { fst: 50, snd: 60 };
+        assert_eq!(*iptr, 50);
+        assert_eq!(p.fst, 50);
+        assert_eq!(p.snd, 60);
+
+        let v0 = vec![32000u16, 32001u16, 32002u16];
+        let mut v1 = vec![0u16, 0u16, 0u16];
+
+        copy(v0.as_ptr().offset(1), v1.as_mut_ptr().offset(1), 1);
+        assert!((v1[0] == 0u16 && v1[1] == 32001u16 && v1[2] == 0u16));
+        copy(v0.as_ptr().offset(2), v1.as_mut_ptr(), 1);
+        assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 0u16));
+        copy(v0.as_ptr(), v1.as_mut_ptr().offset(2), 1);
+        assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 32000u16));
+    }
+}
+
+#[test]
+fn test_is_null() {
+    let p: *const isize = null();
+    assert!(p.is_null());
+
+    let q = p.wrapping_offset(1);
+    assert!(!q.is_null());
+
+    let mp: *mut isize = null_mut();
+    assert!(mp.is_null());
+
+    let mq = mp.wrapping_offset(1);
+    assert!(!mq.is_null());
+
+    // Pointers to unsized types -- slices
+    let s: &mut [u8] = &mut [1, 2, 3];
+    let cs: *const [u8] = s;
+    assert!(!cs.is_null());
+
+    let ms: *mut [u8] = s;
+    assert!(!ms.is_null());
+
+    let cz: *const [u8] = &[];
+    assert!(!cz.is_null());
+
+    let mz: *mut [u8] = &mut [];
+    assert!(!mz.is_null());
+
+    let ncs: *const [u8] = null::<[u8; 3]>();
+    assert!(ncs.is_null());
+
+    let nms: *mut [u8] = null_mut::<[u8; 3]>();
+    assert!(nms.is_null());
+
+    // Pointers to unsized types -- trait objects
+    let ci: *const dyn ToString = &3;
+    assert!(!ci.is_null());
+
+    let mi: *mut dyn ToString = &mut 3;
+    assert!(!mi.is_null());
+
+    let nci: *const dyn ToString = null::<isize>();
+    assert!(nci.is_null());
+
+    let nmi: *mut dyn ToString = null_mut::<isize>();
+    assert!(nmi.is_null());
+
+    extern "C" {
+        type Extern;
+    }
+    let ec: *const Extern = null::<Extern>();
+    assert!(ec.is_null());
+
+    let em: *mut Extern = null_mut::<Extern>();
+    assert!(em.is_null());
+}
+
+#[test]
+fn test_as_ref() {
+    unsafe {
+        let p: *const isize = null();
+        assert_eq!(p.as_ref(), None);
+
+        let q: *const isize = &2;
+        assert_eq!(q.as_ref().unwrap(), &2);
+
+        let p: *mut isize = null_mut();
+        assert_eq!(p.as_ref(), None);
+
+        let q: *mut isize = &mut 2;
+        assert_eq!(q.as_ref().unwrap(), &2);
+
+        // Lifetime inference
+        let u = 2isize;
+        {
+            let p = &u as *const isize;
+            assert_eq!(p.as_ref().unwrap(), &2);
+        }
+
+        // Pointers to unsized types -- slices
+        let s: &mut [u8] = &mut [1, 2, 3];
+        let cs: *const [u8] = s;
+        assert_eq!(cs.as_ref(), Some(&*s));
+
+        let ms: *mut [u8] = s;
+        assert_eq!(ms.as_ref(), Some(&*s));
+
+        let cz: *const [u8] = &[];
+        assert_eq!(cz.as_ref(), Some(&[][..]));
+
+        let mz: *mut [u8] = &mut [];
+        assert_eq!(mz.as_ref(), Some(&[][..]));
+
+        let ncs: *const [u8] = null::<[u8; 3]>();
+        assert_eq!(ncs.as_ref(), None);
+
+        let nms: *mut [u8] = null_mut::<[u8; 3]>();
+        assert_eq!(nms.as_ref(), None);
+
+        // Pointers to unsized types -- trait objects
+        let ci: *const dyn ToString = &3;
+        assert!(ci.as_ref().is_some());
+
+        let mi: *mut dyn ToString = &mut 3;
+        assert!(mi.as_ref().is_some());
+
+        let nci: *const dyn ToString = null::<isize>();
+        assert!(nci.as_ref().is_none());
+
+        let nmi: *mut dyn ToString = null_mut::<isize>();
+        assert!(nmi.as_ref().is_none());
+    }
+}
+
+#[test]
+fn test_as_mut() {
+    unsafe {
+        let p: *mut isize = null_mut();
+        assert!(p.as_mut() == None);
+
+        let q: *mut isize = &mut 2;
+        assert!(q.as_mut().unwrap() == &mut 2);
+
+        // Lifetime inference
+        let mut u = 2isize;
+        {
+            let p = &mut u as *mut isize;
+            assert!(p.as_mut().unwrap() == &mut 2);
+        }
+
+        // Pointers to unsized types -- slices
+        let s: &mut [u8] = &mut [1, 2, 3];
+        let ms: *mut [u8] = s;
+        assert_eq!(ms.as_mut(), Some(&mut [1, 2, 3][..]));
+
+        let mz: *mut [u8] = &mut [];
+        assert_eq!(mz.as_mut(), Some(&mut [][..]));
+
+        let nms: *mut [u8] = null_mut::<[u8; 3]>();
+        assert_eq!(nms.as_mut(), None);
+
+        // Pointers to unsized types -- trait objects
+        let mi: *mut dyn ToString = &mut 3;
+        assert!(mi.as_mut().is_some());
+
+        let nmi: *mut dyn ToString = null_mut::<isize>();
+        assert!(nmi.as_mut().is_none());
+    }
+}
+
+#[test]
+fn test_ptr_addition() {
+    unsafe {
+        let xs = vec![5; 16];
+        let mut ptr = xs.as_ptr();
+        let end = ptr.offset(16);
+
+        while ptr < end {
+            assert_eq!(*ptr, 5);
+            ptr = ptr.offset(1);
+        }
+
+        let mut xs_mut = xs;
+        let mut m_ptr = xs_mut.as_mut_ptr();
+        let m_end = m_ptr.offset(16);
+
+        while m_ptr < m_end {
+            *m_ptr += 5;
+            m_ptr = m_ptr.offset(1);
+        }
+
+        assert!(xs_mut == vec![10; 16]);
+    }
+}
+
+#[test]
+fn test_ptr_subtraction() {
+    unsafe {
+        let xs = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+        let mut idx = 9;
+        let ptr = xs.as_ptr();
+
+        while idx >= 0 {
+            assert_eq!(*(ptr.offset(idx as isize)), idx as isize);
+            idx = idx - 1;
+        }
+
+        let mut xs_mut = xs;
+        let m_start = xs_mut.as_mut_ptr();
+        let mut m_ptr = m_start.offset(9);
+
+        loop {
+            *m_ptr += *m_ptr;
+            if m_ptr == m_start {
+                break;
+            }
+            m_ptr = m_ptr.offset(-1);
+        }
+
+        assert_eq!(xs_mut, [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]);
+    }
+}
+
+#[test]
+fn test_set_memory() {
+    let mut xs = [0u8; 20];
+    let ptr = xs.as_mut_ptr();
+    unsafe {
+        write_bytes(ptr, 5u8, xs.len());
+    }
+    assert!(xs == [5u8; 20]);
+}
+
+#[test]
+fn test_set_memory_const() {
+    const XS: [u8; 20] = {
+        let mut xs = [0u8; 20];
+        let ptr = xs.as_mut_ptr();
+        unsafe {
+            ptr.write_bytes(5u8, xs.len());
+        }
+        xs
+    };
+
+    assert!(XS == [5u8; 20]);
+}
+
+#[test]
+fn test_unsized_nonnull() {
+    let xs: &[i32] = &[1, 2, 3];
+    let ptr = unsafe { NonNull::new_unchecked(xs as *const [i32] as *mut [i32]) };
+    let ys = unsafe { ptr.as_ref() };
+    let zs: &[i32] = &[1, 2, 3];
+    assert!(ys == zs);
+}
+
+#[test]
+fn test_const_nonnull_new() {
+    const {
+        assert!(NonNull::new(core::ptr::null_mut::<()>()).is_none());
+
+        let value = &mut 0u32;
+        let mut ptr = NonNull::new(value).unwrap();
+        unsafe { *ptr.as_mut() = 42 };
+
+        let reference = unsafe { &*ptr.as_ref() };
+        assert!(*reference == *value);
+        assert!(*reference == 42);
+    };
+}
+
+#[test]
+#[cfg(unix)] // printf may not be available on other platforms
+#[allow(deprecated)] // For SipHasher
+pub fn test_variadic_fnptr() {
+    use core::ffi;
+    use core::hash::{Hash, SipHasher};
+    extern "C" {
+        // This needs to use the correct function signature even though it isn't called as some
+        // codegen backends make it UB to declare a function with multiple conflicting signatures
+        // (like LLVM) while others straight up return an error (like Cranelift).
+        fn printf(_: *const ffi::c_char, ...) -> ffi::c_int;
+    }
+    let p: unsafe extern "C" fn(*const ffi::c_char, ...) -> ffi::c_int = printf;
+    let q = p.clone();
+    assert_eq!(p, q);
+    assert!(!(p < q));
+    let mut s = SipHasher::new();
+    assert_eq!(p.hash(&mut s), q.hash(&mut s));
+}
+
+#[test]
+fn write_unaligned_drop() {
+    thread_local! {
+        static DROPS: RefCell<Vec<u32>> = RefCell::new(Vec::new());
+    }
+
+    struct Dropper(u32);
+
+    impl Drop for Dropper {
+        fn drop(&mut self) {
+            DROPS.with(|d| d.borrow_mut().push(self.0));
+        }
+    }
+
+    {
+        let c = Dropper(0);
+        let mut t = Dropper(1);
+        unsafe {
+            write_unaligned(&mut t, c);
+        }
+    }
+    DROPS.with(|d| assert_eq!(*d.borrow(), [0]));
+}
+
+#[test]
+fn align_offset_zst() {
+    // For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
+    // all, because no amount of elements will align the pointer.
+    let mut p = 1;
+    while p < 1024 {
+        assert_eq!(ptr::invalid::<()>(p).align_offset(p), 0);
+        if p != 1 {
+            assert_eq!(ptr::invalid::<()>(p + 1).align_offset(p), !0);
+        }
+        p = (p + 1).next_power_of_two();
+    }
+}
+
+#[test]
+fn align_offset_stride_one() {
+    // For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
+    // number of bytes.
+    let mut align = 1;
+    while align < 1024 {
+        for ptr in 1..2 * align {
+            let expected = ptr % align;
+            let offset = if expected == 0 { 0 } else { align - expected };
+            assert_eq!(
+                ptr::invalid::<u8>(ptr).align_offset(align),
+                offset,
+                "ptr = {}, align = {}, size = 1",
+                ptr,
+                align
+            );
+        }
+        align = (align + 1).next_power_of_two();
+    }
+}
+
+#[test]
+fn align_offset_various_strides() {
+    unsafe fn test_stride<T>(ptr: *const T, align: usize) -> bool {
+        let numptr = ptr as usize;
+        let mut expected = usize::MAX;
+        // Naive but definitely correct way to find the *first* aligned element of stride::<T>.
+        for el in 0..align {
+            if (numptr + el * ::std::mem::size_of::<T>()) % align == 0 {
+                expected = el;
+                break;
+            }
+        }
+        let got = ptr.align_offset(align);
+        if got != expected {
+            eprintln!(
+                "aligning {:p} (with stride of {}) to {}, expected {}, got {}",
+                ptr,
+                ::std::mem::size_of::<T>(),
+                align,
+                expected,
+                got
+            );
+            return true;
+        }
+        return false;
+    }
+
+    // For pointers of stride != 1, we verify the algorithm against the naivest possible
+    // implementation
+    let mut align = 1;
+    let mut x = false;
+    // Miri is too slow
+    let limit = if cfg!(miri) { 32 } else { 1024 };
+    while align < limit {
+        for ptr in 1usize..4 * align {
+            unsafe {
+                #[repr(packed)]
+                struct A3(u16, u8);
+                x |= test_stride::<A3>(ptr::invalid::<A3>(ptr), align);
+
+                struct A4(u32);
+                x |= test_stride::<A4>(ptr::invalid::<A4>(ptr), align);
+
+                #[repr(packed)]
+                struct A5(u32, u8);
+                x |= test_stride::<A5>(ptr::invalid::<A5>(ptr), align);
+
+                #[repr(packed)]
+                struct A6(u32, u16);
+                x |= test_stride::<A6>(ptr::invalid::<A6>(ptr), align);
+
+                #[repr(packed)]
+                struct A7(u32, u16, u8);
+                x |= test_stride::<A7>(ptr::invalid::<A7>(ptr), align);
+
+                #[repr(packed)]
+                struct A8(u32, u32);
+                x |= test_stride::<A8>(ptr::invalid::<A8>(ptr), align);
+
+                #[repr(packed)]
+                struct A9(u32, u32, u8);
+                x |= test_stride::<A9>(ptr::invalid::<A9>(ptr), align);
+
+                #[repr(packed)]
+                struct A10(u32, u32, u16);
+                x |= test_stride::<A10>(ptr::invalid::<A10>(ptr), align);
+
+                x |= test_stride::<u32>(ptr::invalid::<u32>(ptr), align);
+                x |= test_stride::<u128>(ptr::invalid::<u128>(ptr), align);
+            }
+        }
+        align = (align + 1).next_power_of_two();
+    }
+    assert!(!x);
+}
+
+#[test]
+fn offset_from() {
+    let mut a = [0; 5];
+    let ptr1: *mut i32 = &mut a[1];
+    let ptr2: *mut i32 = &mut a[3];
+    unsafe {
+        assert_eq!(ptr2.offset_from(ptr1), 2);
+        assert_eq!(ptr1.offset_from(ptr2), -2);
+        assert_eq!(ptr1.offset(2), ptr2);
+        assert_eq!(ptr2.offset(-2), ptr1);
+    }
+}
+
+#[test]
+fn ptr_metadata() {
+    struct Unit;
+    struct Pair<A, B: ?Sized>(A, B);
+    extern "C" {
+        type Extern;
+    }
+    let () = metadata(&());
+    let () = metadata(&Unit);
+    let () = metadata(&4_u32);
+    let () = metadata(&String::new());
+    let () = metadata(&Some(4_u32));
+    let () = metadata(&ptr_metadata);
+    let () = metadata(&|| {});
+    let () = metadata(&[4, 7]);
+    let () = metadata(&(4, String::new()));
+    let () = metadata(&Pair(4, String::new()));
+    let () = metadata(ptr::null::<()>() as *const Extern);
+    let () = metadata(ptr::null::<()>() as *const <&u32 as std::ops::Deref>::Target);
+
+    assert_eq!(metadata("foo"), 3_usize);
+    assert_eq!(metadata(&[4, 7][..]), 2_usize);
+
+    let dst_tuple: &(bool, [u8]) = &(true, [0x66, 0x6F, 0x6F]);
+    let dst_struct: &Pair<bool, [u8]> = &Pair(true, [0x66, 0x6F, 0x6F]);
+    assert_eq!(metadata(dst_tuple), 3_usize);
+    assert_eq!(metadata(dst_struct), 3_usize);
+    unsafe {
+        let dst_tuple: &(bool, str) = std::mem::transmute(dst_tuple);
+        let dst_struct: &Pair<bool, str> = std::mem::transmute(dst_struct);
+        assert_eq!(&dst_tuple.1, "foo");
+        assert_eq!(&dst_struct.1, "foo");
+        assert_eq!(metadata(dst_tuple), 3_usize);
+        assert_eq!(metadata(dst_struct), 3_usize);
+    }
+
+    let vtable_1: DynMetadata<dyn Debug> = metadata(&4_u16 as &dyn Debug);
+    let vtable_2: DynMetadata<dyn Display> = metadata(&4_u16 as &dyn Display);
+    let vtable_3: DynMetadata<dyn Display> = metadata(&4_u32 as &dyn Display);
+    let vtable_4: DynMetadata<dyn Display> = metadata(&(true, 7_u32) as &(bool, dyn Display));
+    let vtable_5: DynMetadata<dyn Display> =
+        metadata(&Pair(true, 7_u32) as &Pair<bool, dyn Display>);
+    unsafe {
+        let address_1: *const () = std::mem::transmute(vtable_1);
+        let address_2: *const () = std::mem::transmute(vtable_2);
+        let address_3: *const () = std::mem::transmute(vtable_3);
+        let address_4: *const () = std::mem::transmute(vtable_4);
+        let address_5: *const () = std::mem::transmute(vtable_5);
+        // Different trait => different vtable pointer
+        assert_ne!(address_1, address_2);
+        // Different erased type => different vtable pointer
+        assert_ne!(address_2, address_3);
+        // Same erased type and same trait => same vtable pointer
+        assert_eq!(address_3, address_4);
+        assert_eq!(address_3, address_5);
+    }
+}
+
+#[test]
+fn ptr_metadata_bounds() {
+    fn metadata_eq_method_address<T: ?Sized>() -> usize {
+        // The `Metadata` associated type has an `Ord` bound, so this is valid:
+        <<T as Pointee>::Metadata as PartialEq>::eq as usize
+    }
+    // "Synthetic" trait impls generated by the compiler like those of `Pointee`
+    // are not checked for bounds of associated type.
+    // So with a buggy libcore we could have both:
+    // * `<dyn Display as Pointee>::Metadata == DynMetadata`
+    // * `DynMetadata: !PartialEq`
+    // … and cause an ICE here:
+    metadata_eq_method_address::<dyn Display>();
+
+    // For this reason, let’s check here that bounds are satisfied:
+
+    let _ = static_assert_expected_bounds_for_metadata::<()>;
+    let _ = static_assert_expected_bounds_for_metadata::<usize>;
+    let _ = static_assert_expected_bounds_for_metadata::<DynMetadata<dyn Display>>;
+    fn _static_assert_associated_type<T: ?Sized>() {
+        let _ = static_assert_expected_bounds_for_metadata::<<T as Pointee>::Metadata>;
+    }
+
+    fn static_assert_expected_bounds_for_metadata<Meta>()
+    where
+        // Keep this in sync with the associated type in `library/core/src/ptr/metadata.rs`
+        Meta: Copy + Send + Sync + Ord + std::hash::Hash + Unpin,
+    {
+    }
+}
+
+#[test]
+fn dyn_metadata() {
+    #[derive(Debug)]
+    #[repr(align(32))]
+    struct Something([u8; 47]);
+
+    let value = Something([0; 47]);
+    let trait_object: &dyn Debug = &value;
+    let meta = metadata(trait_object);
+
+    assert_eq!(meta.size_of(), 64);
+    assert_eq!(meta.size_of(), std::mem::size_of::<Something>());
+    assert_eq!(meta.align_of(), 32);
+    assert_eq!(meta.align_of(), std::mem::align_of::<Something>());
+    assert_eq!(meta.layout(), std::alloc::Layout::new::<Something>());
+
+    assert!(format!("{meta:?}").starts_with("DynMetadata(0x"));
+}
+
+#[test]
+fn from_raw_parts() {
+    let mut value = 5_u32;
+    let address = &mut value as *mut _ as *mut ();
+    let trait_object: &dyn Display = &mut value;
+    let vtable = metadata(trait_object);
+    let trait_object = NonNull::from(trait_object);
+
+    assert_eq!(ptr::from_raw_parts(address, vtable), trait_object.as_ptr());
+    assert_eq!(ptr::from_raw_parts_mut(address, vtable), trait_object.as_ptr());
+    assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), vtable), trait_object);
+
+    let mut array = [5_u32, 5, 5, 5, 5];
+    let address = &mut array as *mut _ as *mut ();
+    let array_ptr = NonNull::from(&mut array);
+    let slice_ptr = NonNull::from(&mut array[..]);
+
+    assert_eq!(ptr::from_raw_parts(address, ()), array_ptr.as_ptr());
+    assert_eq!(ptr::from_raw_parts_mut(address, ()), array_ptr.as_ptr());
+    assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), ()), array_ptr);
+
+    assert_eq!(ptr::from_raw_parts(address, 5), slice_ptr.as_ptr());
+    assert_eq!(ptr::from_raw_parts_mut(address, 5), slice_ptr.as_ptr());
+    assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), 5), slice_ptr);
+}
+
+#[test]
+fn thin_box() {
+    let foo = ThinBox::<dyn Display>::new(4);
+    assert_eq!(foo.to_string(), "4");
+    drop(foo);
+    let bar = ThinBox::<dyn Display>::new(7);
+    assert_eq!(bar.to_string(), "7");
+
+    // A slightly more interesting library that could be built on top of metadata APIs.
+    //
+    // * It could be generalized to any `T: ?Sized` (not just trait object)
+    //   if `{size,align}_of_for_meta<T: ?Sized>(T::Metadata)` are added.
+    // * Constructing a `ThinBox` without consuming and deallocating a `Box`
+    //   requires either the unstable `Unsize` marker trait,
+    //   or the unstable `unsized_locals` language feature,
+    //   or taking `&dyn T` and restricting to `T: Copy`.
+
+    use std::alloc::*;
+    use std::marker::PhantomData;
+
+    struct ThinBox<T>
+    where
+        T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
+    {
+        ptr: NonNull<DynMetadata<T>>,
+        phantom: PhantomData<T>,
+    }
+
+    impl<T> ThinBox<T>
+    where
+        T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
+    {
+        pub fn new<Value: std::marker::Unsize<T>>(value: Value) -> Self {
+            let unsized_: &T = &value;
+            let meta = metadata(unsized_);
+            let meta_layout = Layout::for_value(&meta);
+            let value_layout = Layout::for_value(&value);
+            let (layout, offset) = meta_layout.extend(value_layout).unwrap();
+            // `DynMetadata` is pointer-sized:
+            assert!(layout.size() > 0);
+            // If `ThinBox<T>` is generalized to any `T: ?Sized`,
+            // handle ZSTs with a dangling pointer without going through `alloc()`,
+            // like `Box<T>` does.
+            unsafe {
+                let ptr = NonNull::new(alloc(layout))
+                    .unwrap_or_else(|| handle_alloc_error(layout))
+                    .cast::<DynMetadata<T>>();
+                ptr.as_ptr().write(meta);
+                ptr.cast::<u8>().as_ptr().add(offset).cast::<Value>().write(value);
+                Self { ptr, phantom: PhantomData }
+            }
+        }
+
+        fn meta(&self) -> DynMetadata<T> {
+            unsafe { *self.ptr.as_ref() }
+        }
+
+        fn layout(&self) -> (Layout, usize) {
+            let meta = self.meta();
+            Layout::for_value(&meta).extend(meta.layout()).unwrap()
+        }
+
+        fn value_ptr(&self) -> *const T {
+            let (_, offset) = self.layout();
+            let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
+            ptr::from_raw_parts(data_ptr.cast(), self.meta())
+        }
+
+        fn value_mut_ptr(&mut self) -> *mut T {
+            let (_, offset) = self.layout();
+            // FIXME: can this line be shared with the same in `value_ptr()`
+            // without upsetting Stacked Borrows?
+            let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
+            from_raw_parts_mut(data_ptr.cast(), self.meta())
+        }
+    }
+
+    impl<T> std::ops::Deref for ThinBox<T>
+    where
+        T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
+    {
+        type Target = T;
+
+        fn deref(&self) -> &T {
+            unsafe { &*self.value_ptr() }
+        }
+    }
+
+    impl<T> std::ops::DerefMut for ThinBox<T>
+    where
+        T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
+    {
+        fn deref_mut(&mut self) -> &mut T {
+            unsafe { &mut *self.value_mut_ptr() }
+        }
+    }
+
+    impl<T> std::ops::Drop for ThinBox<T>
+    where
+        T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
+    {
+        fn drop(&mut self) {
+            let (layout, _) = self.layout();
+            unsafe {
+                drop_in_place::<T>(&mut **self);
+                dealloc(self.ptr.cast().as_ptr(), layout);
+            }
+        }
+    }
+}
+
+#[test]
+fn nonnull_tagged_pointer_with_provenance() {
+    let raw_pointer = Box::into_raw(Box::new(10));
+
+    let mut p = TaggedPointer::new(raw_pointer).unwrap();
+    assert_eq!(p.tag(), 0);
+
+    p.set_tag(1);
+    assert_eq!(p.tag(), 1);
+    assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);
+
+    p.set_tag(3);
+    assert_eq!(p.tag(), 3);
+    assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);
+
+    unsafe { Box::from_raw(p.pointer().as_ptr()) };
+
+    /// A non-null pointer type which carries several bits of metadata and maintains provenance.
+    #[repr(transparent)]
+    pub struct TaggedPointer<T>(NonNull<T>);
+
+    impl<T> Clone for TaggedPointer<T> {
+        fn clone(&self) -> Self {
+            Self(self.0)
+        }
+    }
+
+    impl<T> Copy for TaggedPointer<T> {}
+
+    impl<T> TaggedPointer<T> {
+        /// The ABI-required minimum alignment of the `P` type.
+        pub const ALIGNMENT: usize = core::mem::align_of::<T>();
+        /// A mask for data-carrying bits of the address.
+        pub const DATA_MASK: usize = !Self::ADDRESS_MASK;
+        /// Number of available bits of storage in the address.
+        pub const NUM_BITS: u32 = Self::ALIGNMENT.trailing_zeros();
+        /// A mask for the non-data-carrying bits of the address.
+        pub const ADDRESS_MASK: usize = usize::MAX << Self::NUM_BITS;
+
+        /// Create a new tagged pointer from a possibly null pointer.
+        pub fn new(pointer: *mut T) -> Option<TaggedPointer<T>> {
+            Some(TaggedPointer(NonNull::new(pointer)?))
+        }
+
+        /// Consume this tagged pointer and produce a raw mutable pointer to the
+        /// memory location.
+        pub fn pointer(self) -> NonNull<T> {
+            // SAFETY: The `addr` guaranteed to have bits set in the Self::ADDRESS_MASK, so the result will be non-null.
+            self.0.map_addr(|addr| unsafe {
+                NonZeroUsize::new_unchecked(addr.get() & Self::ADDRESS_MASK)
+            })
+        }
+
+        /// Consume this tagged pointer and produce the data it carries.
+        pub fn tag(&self) -> usize {
+            self.0.addr().get() & Self::DATA_MASK
+        }
+
+        /// Update the data this tagged pointer carries to a new value.
+        pub fn set_tag(&mut self, data: usize) {
+            assert_eq!(
+                data & Self::ADDRESS_MASK,
+                0,
+                "cannot set more data beyond the lowest NUM_BITS"
+            );
+            let data = data & Self::DATA_MASK;
+
+            // SAFETY: This value will always be non-zero because the upper bits (from
+            // ADDRESS_MASK) will always be non-zero. This a property of the type and its
+            // construction.
+            self.0 = self.0.map_addr(|addr| unsafe {
+                NonZeroUsize::new_unchecked((addr.get() & Self::ADDRESS_MASK) | data)
+            })
+        }
+    }
+}
+
+#[test]
+fn swap_copy_untyped() {
+    // We call `{swap,copy}{,_nonoverlapping}` at `bool` type on data that is not a valid bool.
+    // These should all do untyped copies, so this should work fine.
+    let mut x = 5u8;
+    let mut y = 6u8;
+
+    let ptr1 = &mut x as *mut u8 as *mut bool;
+    let ptr2 = &mut y as *mut u8 as *mut bool;
+
+    unsafe {
+        ptr::swap(ptr1, ptr2);
+        ptr::swap_nonoverlapping(ptr1, ptr2, 1);
+    }
+    assert_eq!(x, 5);
+    assert_eq!(y, 6);
+
+    unsafe {
+        ptr::copy(ptr1, ptr2, 1);
+        ptr::copy_nonoverlapping(ptr1, ptr2, 1);
+    }
+    assert_eq!(x, 5);
+    assert_eq!(y, 5);
+}
+
+#[test]
+fn test_const_copy() {
+    const {
+        let ptr1 = &1;
+        let mut ptr2 = &666;
+
+        // Copy ptr1 to ptr2, bytewise.
+        unsafe {
+            ptr::copy(
+                &ptr1 as *const _ as *const MaybeUninit<u8>,
+                &mut ptr2 as *mut _ as *mut MaybeUninit<u8>,
+                mem::size_of::<&i32>(),
+            );
+        }
+
+        // Make sure they still work.
+        assert!(*ptr1 == 1);
+        assert!(*ptr2 == 1);
+    };
+
+    const {
+        let ptr1 = &1;
+        let mut ptr2 = &666;
+
+        // Copy ptr1 to ptr2, bytewise.
+        unsafe {
+            ptr::copy_nonoverlapping(
+                &ptr1 as *const _ as *const MaybeUninit<u8>,
+                &mut ptr2 as *mut _ as *mut MaybeUninit<u8>,
+                mem::size_of::<&i32>(),
+            );
+        }
+
+        // Make sure they still work.
+        assert!(*ptr1 == 1);
+        assert!(*ptr2 == 1);
+    };
+}