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Update TransparentWrapper asserts #232

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merged 2 commits into from
Apr 10, 2024
Merged

Update TransparentWrapper asserts #232

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5efbd36
Update TransparentWrapper asserts.
zachs18 Apr 1, 2024
2e18295
Update TransparentWrapperAlloc assert comments.
zachs18 Apr 1, 2024
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30 changes: 30 additions & 0 deletions src/allocation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -531,6 +531,11 @@ pub trait TransparentWrapperAlloc<Inner: ?Sized>:
/// type.
#[inline]
fn wrap_box(s: Box<Inner>) -> Box<Self> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());

unsafe {
Expand All @@ -555,6 +560,11 @@ pub trait TransparentWrapperAlloc<Inner: ?Sized>:
/// wrapper type.
#[inline]
fn wrap_rc(s: Rc<Inner>) -> Rc<Self> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());

unsafe {
Expand All @@ -578,6 +588,11 @@ pub trait TransparentWrapperAlloc<Inner: ?Sized>:
#[inline]
#[cfg(target_has_atomic = "ptr")]
fn wrap_arc(s: Arc<Inner>) -> Arc<Self> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());

unsafe {
Expand Down Expand Up @@ -621,6 +636,11 @@ pub trait TransparentWrapperAlloc<Inner: ?Sized>:
/// type.
#[inline]
fn peel_box(s: Box<Self>) -> Box<Inner> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());

unsafe {
Expand All @@ -645,6 +665,11 @@ pub trait TransparentWrapperAlloc<Inner: ?Sized>:
/// inner type.
#[inline]
fn peel_rc(s: Rc<Self>) -> Rc<Inner> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());

unsafe {
Expand All @@ -668,6 +693,11 @@ pub trait TransparentWrapperAlloc<Inner: ?Sized>:
#[inline]
#[cfg(target_has_atomic = "ptr")]
fn peel_arc(s: Arc<Self>) -> Arc<Inner> {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());

unsafe {
Expand Down
77 changes: 47 additions & 30 deletions src/transparent.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -89,9 +89,8 @@ use super::*;
///
/// ## Deriving
///
/// When deriving, the non-wrapped fields must uphold all the normal requirements,
/// and must also be `Zeroable`.
///
/// When deriving, the non-wrapped fields must uphold all the normal
/// requirements, and must also be `Zeroable`.
#[cfg_attr(feature = "derive", doc = "```")]
#[cfg_attr(
not(feature = "derive"),
Expand All @@ -108,7 +107,6 @@ use super::*;
/// ```
///
/// Here, an error will occur, because `MyZst` does not implement `Zeroable`.
///
#[cfg_attr(feature = "derive", doc = "```compile_fail")]
#[cfg_attr(
not(feature = "derive"),
Expand All @@ -131,6 +129,8 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
Self: Sized,
Inner: Sized,
{
assert!(size_of::<Inner>() == size_of::<Self>());
assert!(align_of::<Inner>() == align_of::<Self>());
// SAFETY: The unsafe contract requires that `Self` and `Inner` have
// identical representations.
unsafe { transmute!(s) }
Expand All @@ -140,8 +140,13 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
/// type.
#[inline]
fn wrap_ref(s: &Inner) -> &Self {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is the best we can do to assert their metadata is the same type
// on stable.
assert!(size_of::<*const Inner>() == size_of::<*const Self>());
unsafe {
assert!(size_of::<*const Inner>() == size_of::<*const Self>());
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the sizes are unspecified.
Expand All @@ -158,8 +163,12 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
/// the wrapper type.
#[inline]
fn wrap_mut(s: &mut Inner) -> &mut Self {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is about the best we can do on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the sizes are unspecified.
Expand All @@ -179,13 +188,11 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
Self: Sized,
Inner: Sized,
{
unsafe {
assert!(size_of::<*const Inner>() == size_of::<*const Self>());
assert!(align_of::<*const Inner>() == align_of::<*const Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
core::slice::from_raw_parts(s.as_ptr() as *const Self, s.len())
}
assert!(size_of::<Inner>() == size_of::<Self>());
assert!(align_of::<Inner>() == align_of::<Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
unsafe { core::slice::from_raw_parts(s.as_ptr() as *const Self, s.len()) }
}

/// Convert a mutable slice to the inner type into a mutable slice to the
Expand All @@ -196,11 +203,11 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
Self: Sized,
Inner: Sized,
{
assert!(size_of::<Inner>() == size_of::<Self>());
assert!(align_of::<Inner>() == align_of::<Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
unsafe {
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
assert!(align_of::<*mut Inner>() == align_of::<*mut Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
core::slice::from_raw_parts_mut(s.as_mut_ptr() as *mut Self, s.len())
}
}
Expand All @@ -212,15 +219,23 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
Self: Sized,
Inner: Sized,
{
assert!(size_of::<Inner>() == size_of::<Self>());
assert!(align_of::<Inner>() == align_of::<Self>());
// SAFETY: The unsafe contract requires that `Self` and `Inner` have
// identical representations.
unsafe { transmute!(s) }
}

/// Convert a reference to the wrapper type into a reference to the inner
/// type.
#[inline]
fn peel_ref(s: &Self) -> &Inner {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is about the best we can do on stable.
assert!(size_of::<*const Inner>() == size_of::<*const Self>());
unsafe {
assert!(size_of::<*const Inner>() == size_of::<*const Self>());
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the sizes are unspecified.
Expand All @@ -237,8 +252,12 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
/// to the inner type.
#[inline]
fn peel_mut(s: &mut Self) -> &mut Inner {
// The unsafe contract requires that these two have
// identical representations, and thus identical pointer metadata.
// Assert that Self and Inner have the same pointer size,
// which is about the best we can do on stable.
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
unsafe {
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
// A pointer cast doesn't work here because rustc can't tell that
// the vtables match (because of the `?Sized` restriction relaxation).
// A `transmute` doesn't work because the sizes are unspecified.
Expand All @@ -258,13 +277,11 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
Self: Sized,
Inner: Sized,
{
unsafe {
assert!(size_of::<*const Inner>() == size_of::<*const Self>());
assert!(align_of::<*const Inner>() == align_of::<*const Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
core::slice::from_raw_parts(s.as_ptr() as *const Inner, s.len())
}
assert!(size_of::<Inner>() == size_of::<Self>());
assert!(align_of::<Inner>() == align_of::<Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
unsafe { core::slice::from_raw_parts(s.as_ptr() as *const Inner, s.len()) }
}

/// Convert a mutable slice to the wrapped type into a mutable slice to the
Expand All @@ -275,11 +292,11 @@ pub unsafe trait TransparentWrapper<Inner: ?Sized> {
Self: Sized,
Inner: Sized,
{
assert!(size_of::<Inner>() == size_of::<Self>());
assert!(align_of::<Inner>() == align_of::<Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
unsafe {
assert!(size_of::<*mut Inner>() == size_of::<*mut Self>());
assert!(align_of::<*mut Inner>() == align_of::<*mut Self>());
// SAFETY: The unsafe contract requires that these two have
// identical representations (size and alignment).
core::slice::from_raw_parts_mut(s.as_mut_ptr() as *mut Inner, s.len())
}
}
Expand Down
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