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Merged
joshlf merged 1 commit into from
Jan 29, 2026
Merged

Add generic Ptr::try_with #2946

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30 changes: 30 additions & 0 deletions src/error.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -653,6 +653,20 @@ impl<Src: Clone, Dst: ?Sized + TryFromBytes> Clone for ValidityError<Src, Dst> {
}
}

// SAFETY: `ValidityError` contains a single `Self::Inner = Src`, and no other
// non-ZST fields. `map` passes ownership of `self`'s sole `Self::Inner` to `f`.
unsafe impl<Src, NewSrc, Dst> crate::pointer::TryWithError<NewSrc>
for crate::ValidityError<Src, Dst>
where
Dst: TryFromBytes + ?Sized,
{
type Inner = Src;
type Mapped = crate::ValidityError<NewSrc, Dst>;
fn map<F: FnOnce(Src) -> NewSrc>(self, f: F) -> Self::Mapped {
self.map_src(f)
}
}

impl<Src: PartialEq, Dst: ?Sized + TryFromBytes> PartialEq for ValidityError<Src, Dst> {
#[inline]
fn eq(&self, other: &Self) -> bool {
Expand Down Expand Up @@ -775,6 +789,22 @@ impl<Src, Dst: ?Sized> CastError<Src, Dst> {
}
}

// SAFETY: `CastError` is either a single `AlignmentError` or a single
// `SizeError`. In either case, it contains a single `Self::Inner = Src`, and no
// other non-ZST fields. `map` passes ownership of `self`'s sole `Self::Inner`
// to `f`.
unsafe impl<Src, NewSrc, Dst> crate::pointer::TryWithError<NewSrc> for crate::CastError<Src, Dst>
where
Dst: ?Sized,
{
type Inner = Src;
type Mapped = crate::CastError<NewSrc, Dst>;

fn map<F: FnOnce(Src) -> NewSrc>(self, f: F) -> Self::Mapped {
self.map_src(f)
}
}

impl<Src, Dst: ?Sized + Unaligned> From<CastError<Src, Dst>> for SizeError<Src, Dst> {
/// Infallibly extracts the [`SizeError`] from this `CastError` since `Dst`
/// is unaligned.
Expand Down
2 changes: 1 addition & 1 deletion src/pointer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ pub use {inner::PtrInner, transmute::*};
#[doc(hidden)]
pub use {
invariant::{BecauseExclusive, BecauseImmutable, Read},
ptr::Ptr,
ptr::*,
};

use crate::wrappers::ReadOnly;
Expand Down
84 changes: 84 additions & 0 deletions src/pointer/ptr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -795,6 +795,7 @@ mod _transitions {
}

/// Casts of the referent type.
pub(crate) use _casts::TryWithError;
mod _casts {
use core::cell::UnsafeCell;

Expand Down Expand Up @@ -912,6 +913,89 @@ mod _casts {
let tag = unsafe { tag.assume_alignment() };
tag.unify_invariants()
}

/// Attempts to transform the pointer, restoring the original on
/// failure.
///
/// # Safety
///
/// If `I::Aliasing != Shared`, then if `f` returns `Err(err)`, no copy
/// of `f`'s argument must exist outside of `err`.
#[inline(always)]
pub(crate) unsafe fn try_with_unchecked<U, J, E, F>(
self,
f: F,
) -> Result<Ptr<'a, U, J>, E::Mapped>
where
U: 'a + ?Sized,
J: Invariants<Aliasing = I::Aliasing>,
E: TryWithError<Self>,
F: FnOnce(Ptr<'a, T, I>) -> Result<Ptr<'a, U, J>, E>,
{
let old_inner = self.as_inner();
#[rustfmt::skip]
let res = f(self).map_err(#[inline(always)] move |err: E| {
err.map(#[inline(always)] |src| {
drop(src);

// SAFETY:
// 0. Aliasing is either `Shared` or `Exclusive`:
// - If aliasing is `Shared`, then it cannot violate
// aliasing make another copy of this pointer (in fact,
// using `I::Aliasing = Shared`, we could have just
// cloned `self`).
// - If aliasing is `Exclusive`, then `f` is not allowed
// to make another copy of `self`. In `map_err`, we are
// consuming the only value in the returned `Result`.
// By invariant on `E: TryWithError<Self>`, that `err:
// E` only contains a single `Self` and no other
// non-ZST fields which could be `Ptr`s or references
// to `self`'s referent. By the same invariant, `map`
// consumes this single `Self` and passes it to this
// closure. Since `self` was, by invariant on
// `Exclusive`, the only `Ptr` or reference live for
// `'a` with this referent, and since we `drop(src)`
// above, there are no copies left, and so we are
// creating the only copy.
// 1. `self` conforms to `I::Aliasing` by invariant on
// `Ptr`, and `old_inner` has the same address, so it
// does too.
// 2. `f` could not have violated `self`'s validity without
// itself being unsound. Assuming that `f` is sound, the
// referent of `self` is still valid for `T`.
unsafe { Ptr::from_inner(old_inner) }
})
});
res
}

/// Attempts to transform the pointer, restoring the original on
/// failure.
pub(crate) fn try_with<U, J, E, F>(self, f: F) -> Result<Ptr<'a, U, J>, E::Mapped>
where
U: 'a + ?Sized,
J: Invariants<Aliasing = I::Aliasing>,
E: TryWithError<Self>,
F: FnOnce(Ptr<'a, T, I>) -> Result<Ptr<'a, U, J>, E>,
I: Invariants<Aliasing = Shared>,
{
// SAFETY: `I::Aliasing = Shared`, so the safety condition does not
// apply.
unsafe { self.try_with_unchecked(f) }
}
}

/// # Safety
///
/// `Self` only contains a single `Self::Inner`, and `Self::Mapped` only
/// contains a single `MappedInner`. Other than that, `Self` and
/// `Self::Mapped` contain no non-ZST fields.
///
/// `map` must pass ownership of `self`'s sole `Self::Inner` to `f`.
pub(crate) unsafe trait TryWithError<MappedInner> {
type Inner;
type Mapped;
fn map<F: FnOnce(Self::Inner) -> MappedInner>(self, f: F) -> Self::Mapped;
}

impl<'a, T, I> Ptr<'a, T, I>
Expand Down
52 changes: 19 additions & 33 deletions src/util/macro_util.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,6 @@ use crate::{
pointer::{
cast::CastSized,
invariant::{Aligned, Initialized, Valid},
BecauseInvariantsEq,
},
FromBytes, Immutable, IntoBytes, KnownLayout, Ptr, ReadOnly, TryFromBytes, ValidityError,
};
Expand Down Expand Up @@ -665,33 +664,21 @@ where
Dst: TryFromBytes + Immutable,
{
let ptr = Ptr::from_ref(src);
let ptr = ptr.recall_validity::<Initialized, _>();
let ptr = ptr.cast::<_, CastSized, _>();
match ptr.try_into_valid() {
#[rustfmt::skip]
let res = ptr.try_with(#[inline(always)] |ptr| {
let ptr = ptr.recall_validity::<Initialized, _>();
let ptr = ptr.cast::<_, CastSized, _>();
ptr.try_into_valid()
});
match res {
Ok(ptr) => {
static_assert!(Src, Dst => mem::align_of::<Dst>() <= mem::align_of::<Src>());
// SAFETY: We have checked that `Dst` does not have a stricter
// alignment requirement than `Src`.
let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
Ok(ptr.as_ref())
}
Err(err) => Err(err.map_src(|ptr| {
let ptr = ptr.cast::<_, CastSized, _>();
// SAFETY: `ptr` has the same address as `src: &Src`, which is
// aligned by invariant on `&Src`.
let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
// SAFETY: Because `Src: Immutable` and we create a `Ptr` via
// `Ptr::from_ref`, the resulting `Ptr` is a shared-and-`Immutable`
// `Ptr`, which does not permit mutation of its referent. Therefore,
// no mutation could have happened during the call to
// `try_into_valid` (any such mutation would be unsound).
//
// `try_into_valid` promises to return its original argument, and
// so we know that we are getting back the same `ptr` that we
// originally passed, and that `ptr` was a bit-valid `Src`.
let ptr = unsafe { ptr.assume_valid() };
ptr.as_ref()
})),
Err(err) => Err(err.map_src(Ptr::as_ref)),
}
}

Expand All @@ -714,25 +701,24 @@ where
Dst: TryFromBytes + IntoBytes,
{
let ptr = Ptr::from_mut(src);
let ptr = ptr.recall_validity::<Initialized, (_, (_, _))>();
let ptr = ptr.cast::<_, CastSized, _>();
match ptr.try_into_valid() {
// SAFETY: The provided closure returns the only copy of `ptr`.
#[rustfmt::skip]
let res = unsafe {
ptr.try_with_unchecked(#[inline(always)] |ptr| {
let ptr = ptr.recall_validity::<Initialized, (_, (_, _))>();
let ptr = ptr.cast::<_, CastSized, _>();
ptr.try_into_valid()
})
};
match res {
Ok(ptr) => {
static_assert!(Src, Dst => mem::align_of::<Dst>() <= mem::align_of::<Src>());
// SAFETY: We have checked that `Dst` does not have a stricter
// alignment requirement than `Src`.
let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
Ok(ptr.as_mut())
}
Err(err) => {
Err(err.map_src(|ptr| {
let ptr = ptr.cast::<_, CastSized, _>();
// SAFETY: `ptr` has the same address as `src: &mut Src`, which
// is aligned by invariant on `&mut Src`.
let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
ptr.recall_validity::<_, (_, BecauseInvariantsEq)>().as_mut()
}))
}
Err(err) => Err(err.map_src(Ptr::as_mut)),
}
}

Expand Down
6 changes: 3 additions & 3 deletions zerocopy-derive/tests/ui-nightly/enum.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -482,7 +482,7 @@ help: the trait `PaddingFree<IntoBytes1, 1>` is not implemented for `()`
but trait `PaddingFree<IntoBytes1, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -504,7 +504,7 @@ help: the trait `PaddingFree<IntoBytes2, 3>` is not implemented for `()`
but trait `PaddingFree<IntoBytes2, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -526,7 +526,7 @@ help: the trait `PaddingFree<IntoBytes3, 2>` is not implemented for `()`
but trait `PaddingFree<IntoBytes3, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down
10 changes: 5 additions & 5 deletions zerocopy-derive/tests/ui-nightly/struct.stderr
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -325,7 +325,7 @@ help: the trait `PaddingFree<IntoBytes2, 1>` is not implemented for `()`
but trait `PaddingFree<IntoBytes2, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -347,7 +347,7 @@ help: the trait `PaddingFree<IntoBytes3, 1>` is not implemented for `()`
but trait `PaddingFree<IntoBytes3, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down Expand Up @@ -405,7 +405,7 @@ help: the trait `DynamicPaddingFree<IntoBytes5, true>` is not implemented for `(
but trait `DynamicPaddingFree<IntoBytes5, false>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
83 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
82 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -427,7 +427,7 @@ help: the trait `DynamicPaddingFree<IntoBytes6, true>` is not implemented for `(
but trait `DynamicPaddingFree<IntoBytes6, false>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
83 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
82 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -449,7 +449,7 @@ help: the trait `DynamicPaddingFree<IntoBytes7, true>` is not implemented for `(
but trait `DynamicPaddingFree<IntoBytes7, false>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
83 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
82 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down
6 changes: 3 additions & 3 deletions zerocopy-derive/tests/ui-stable/enum.stderr
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -439,7 +439,7 @@ help: the trait `PaddingFree<IntoBytes1, 1>` is not implemented for `()`
but trait `PaddingFree<IntoBytes1, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -457,7 +457,7 @@ help: the trait `PaddingFree<IntoBytes2, 3>` is not implemented for `()`
but trait `PaddingFree<IntoBytes2, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -475,7 +475,7 @@ help: the trait `PaddingFree<IntoBytes3, 2>` is not implemented for `()`
but trait `PaddingFree<IntoBytes3, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down
10 changes: 5 additions & 5 deletions zerocopy-derive/tests/ui-stable/struct.stderr
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -293,7 +293,7 @@ help: the trait `PaddingFree<IntoBytes2, 1>` is not implemented for `()`
but trait `PaddingFree<IntoBytes2, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -311,7 +311,7 @@ help: the trait `PaddingFree<IntoBytes3, 1>` is not implemented for `()`
but trait `PaddingFree<IntoBytes3, 0>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
65 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
64 | impl<T: ?Sized> PaddingFree<T, 0> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down Expand Up @@ -365,7 +365,7 @@ help: the trait `DynamicPaddingFree<IntoBytes5, true>` is not implemented for `(
but trait `DynamicPaddingFree<IntoBytes5, false>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
83 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
82 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -383,7 +383,7 @@ help: the trait `DynamicPaddingFree<IntoBytes6, true>` is not implemented for `(
but trait `DynamicPaddingFree<IntoBytes6, false>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
83 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
82 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -401,7 +401,7 @@ help: the trait `DynamicPaddingFree<IntoBytes7, true>` is not implemented for `(
but trait `DynamicPaddingFree<IntoBytes7, false>` is implemented for it
--> $WORKSPACE/src/util/macro_util.rs
|
83 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
82 | impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down
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