zerocopy/macros.rs
1// Copyright 2024 The Fuchsia Authors
2//
3// Licensed under the 2-Clause BSD License <LICENSE-BSD or
4// https://opensource.org/license/bsd-2-clause>, Apache License, Version 2.0
5// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
6// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
7// This file may not be copied, modified, or distributed except according to
8// those terms.
9
10/// Safely transmutes a value of one type to a value of another type of the same
11/// size.
12///
13/// This macro behaves like an invocation of this function:
14///
15/// ```ignore
16/// const fn transmute<Src, Dst>(src: Src) -> Dst
17/// where
18/// Src: IntoBytes,
19/// Dst: FromBytes,
20/// size_of::<Src>() == size_of::<Dst>(),
21/// {
22/// # /*
23/// ...
24/// # */
25/// }
26/// ```
27///
28/// However, unlike a function, this macro can only be invoked when the types of
29/// `Src` and `Dst` are completely concrete. The types `Src` and `Dst` are
30/// inferred from the calling context; they cannot be explicitly specified in
31/// the macro invocation.
32///
33/// Note that the `Src` produced by the expression `$e` will *not* be dropped.
34/// Semantically, its bits will be copied into a new value of type `Dst`, the
35/// original `Src` will be forgotten, and the value of type `Dst` will be
36/// returned.
37///
38/// # Examples
39///
40/// ```
41/// # use zerocopy::transmute;
42/// let one_dimensional: [u8; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
43///
44/// let two_dimensional: [[u8; 4]; 2] = transmute!(one_dimensional);
45///
46/// assert_eq!(two_dimensional, [[0, 1, 2, 3], [4, 5, 6, 7]]);
47/// ```
48///
49/// # Use in `const` contexts
50///
51/// This macro can be invoked in `const` contexts.
52#[macro_export]
53macro_rules! transmute {
54 ($e:expr) => {{
55 // NOTE: This must be a macro (rather than a function with trait bounds)
56 // because there's no way, in a generic context, to enforce that two
57 // types have the same size. `core::mem::transmute` uses compiler magic
58 // to enforce this so long as the types are concrete.
59
60 let e = $e;
61 if false {
62 // This branch, though never taken, ensures that the type of `e` is
63 // `IntoBytes` and that the type of this macro invocation expression
64 // is `FromBytes`.
65
66 struct AssertIsIntoBytes<T: $crate::IntoBytes>(T);
67 let _ = AssertIsIntoBytes(e);
68
69 struct AssertIsFromBytes<U: $crate::FromBytes>(U);
70 #[allow(unused, unreachable_code)]
71 let u = AssertIsFromBytes(loop {});
72 u.0
73 } else {
74 // SAFETY: `core::mem::transmute` ensures that the type of `e` and
75 // the type of this macro invocation expression have the same size.
76 // We know this transmute is safe thanks to the `IntoBytes` and
77 // `FromBytes` bounds enforced by the `false` branch.
78 //
79 // We use this reexport of `core::mem::transmute` because we know it
80 // will always be available for crates which are using the 2015
81 // edition of Rust. By contrast, if we were to use
82 // `std::mem::transmute`, this macro would not work for such crates
83 // in `no_std` contexts, and if we were to use
84 // `core::mem::transmute`, this macro would not work in `std`
85 // contexts in which `core` was not manually imported. This is not a
86 // problem for 2018 edition crates.
87 let u = unsafe {
88 // Clippy: We can't annotate the types; this macro is designed
89 // to infer the types from the calling context.
90 #[allow(clippy::missing_transmute_annotations, unnecessary_transmutes)]
91 $crate::util::macro_util::core_reexport::mem::transmute(e)
92 };
93 $crate::util::macro_util::must_use(u)
94 }
95 }}
96}
97
98/// Safely transmutes a mutable or immutable reference of one type to an
99/// immutable reference of another type of the same size and compatible
100/// alignment.
101///
102/// This macro behaves like an invocation of this function:
103///
104/// ```ignore
105/// fn transmute_ref<'src, 'dst, Src, Dst>(src: &'src Src) -> &'dst Dst
106/// where
107/// 'src: 'dst,
108/// Src: IntoBytes + Immutable + ?Sized,
109/// Dst: FromBytes + Immutable + ?Sized,
110/// align_of::<Src>() >= align_of::<Dst>(),
111/// size_compatible::<Src, Dst>(),
112/// {
113/// # /*
114/// ...
115/// # */
116/// }
117/// ```
118///
119/// The types `Src` and `Dst` are inferred from the calling context; they cannot
120/// be explicitly specified in the macro invocation.
121///
122/// # Size compatibility
123///
124/// `transmute_ref!` supports transmuting between `Sized` types or between
125/// unsized (i.e., `?Sized`) types. It supports any transmutation that preserves
126/// the number of bytes of the referent, even if doing so requires updating the
127/// metadata stored in an unsized "fat" reference:
128///
129/// ```
130/// # use zerocopy::transmute_ref;
131/// # use core::mem::size_of_val; // Not in the prelude on our MSRV
132/// let src: &[[u8; 2]] = &[[0, 1], [2, 3]][..];
133/// let dst: &[u8] = transmute_ref!(src);
134///
135/// assert_eq!(src.len(), 2);
136/// assert_eq!(dst.len(), 4);
137/// assert_eq!(dst, [0, 1, 2, 3]);
138/// assert_eq!(size_of_val(src), size_of_val(dst));
139/// ```
140///
141/// # Errors
142///
143/// Violations of the alignment and size compatibility checks are detected
144/// *after* the compiler performs monomorphization. This has two important
145/// consequences.
146///
147/// First, it means that generic code will *never* fail these conditions:
148///
149/// ```
150/// # use zerocopy::{transmute_ref, FromBytes, IntoBytes, Immutable};
151/// fn transmute_ref<Src, Dst>(src: &Src) -> &Dst
152/// where
153/// Src: IntoBytes + Immutable,
154/// Dst: FromBytes + Immutable,
155/// {
156/// transmute_ref!(src)
157/// }
158/// ```
159///
160/// Instead, failures will only be detected once generic code is instantiated
161/// with concrete types:
162///
163/// ```compile_fail,E0080
164/// # use zerocopy::{transmute_ref, FromBytes, IntoBytes, Immutable};
165/// #
166/// # fn transmute_ref<Src, Dst>(src: &Src) -> &Dst
167/// # where
168/// # Src: IntoBytes + Immutable,
169/// # Dst: FromBytes + Immutable,
170/// # {
171/// # transmute_ref!(src)
172/// # }
173/// let src: &u16 = &0;
174/// let dst: &u8 = transmute_ref(src);
175/// ```
176///
177/// Second, the fact that violations are detected after monomorphization means
178/// that `cargo check` will usually not detect errors, even when types are
179/// concrete. Instead, `cargo build` must be used to detect such errors.
180///
181/// # Examples
182///
183/// Transmuting between `Sized` types:
184///
185/// ```
186/// # use zerocopy::transmute_ref;
187/// let one_dimensional: [u8; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
188///
189/// let two_dimensional: &[[u8; 4]; 2] = transmute_ref!(&one_dimensional);
190///
191/// assert_eq!(two_dimensional, &[[0, 1, 2, 3], [4, 5, 6, 7]]);
192/// ```
193///
194/// Transmuting between unsized types:
195///
196/// ```
197/// # use {zerocopy::*, zerocopy_derive::*};
198/// # type u16 = zerocopy::byteorder::native_endian::U16;
199/// # type u32 = zerocopy::byteorder::native_endian::U32;
200/// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
201/// #[repr(C)]
202/// struct SliceDst<T, U> {
203/// t: T,
204/// u: [U],
205/// }
206///
207/// type Src = SliceDst<u32, u16>;
208/// type Dst = SliceDst<u16, u8>;
209///
210/// let src = Src::ref_from_bytes(&[0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
211/// let dst: &Dst = transmute_ref!(src);
212///
213/// assert_eq!(src.t.as_bytes(), [0, 1, 2, 3]);
214/// assert_eq!(src.u.len(), 2);
215/// assert_eq!(src.u.as_bytes(), [4, 5, 6, 7]);
216///
217/// assert_eq!(dst.t.as_bytes(), [0, 1]);
218/// assert_eq!(dst.u, [2, 3, 4, 5, 6, 7]);
219/// ```
220///
221/// # Use in `const` contexts
222///
223/// This macro can be invoked in `const` contexts only when `Src: Sized` and
224/// `Dst: Sized`.
225#[macro_export]
226macro_rules! transmute_ref {
227 ($e:expr) => {{
228 // NOTE: This must be a macro (rather than a function with trait bounds)
229 // because there's no way, in a generic context, to enforce that two
230 // types have the same size or alignment.
231
232 // Ensure that the source type is a reference or a mutable reference
233 // (note that mutable references are implicitly reborrowed here).
234 let e: &_ = $e;
235
236 #[allow(unused, clippy::diverging_sub_expression)]
237 if false {
238 // This branch, though never taken, ensures that the type of `e` is
239 // `&T` where `T: IntoBytes + Immutable`, and that the type of this
240 // macro expression is `&U` where `U: FromBytes + Immutable`.
241
242 struct AssertSrcIsIntoBytes<'a, T: ?::core::marker::Sized + $crate::IntoBytes>(&'a T);
243 struct AssertSrcIsImmutable<'a, T: ?::core::marker::Sized + $crate::Immutable>(&'a T);
244 struct AssertDstIsFromBytes<'a, U: ?::core::marker::Sized + $crate::FromBytes>(&'a U);
245 struct AssertDstIsImmutable<'a, T: ?::core::marker::Sized + $crate::Immutable>(&'a T);
246
247 let _ = AssertSrcIsIntoBytes(e);
248 let _ = AssertSrcIsImmutable(e);
249
250 if true {
251 #[allow(unused, unreachable_code)]
252 let u = AssertDstIsFromBytes(loop {});
253 u.0
254 } else {
255 #[allow(unused, unreachable_code)]
256 let u = AssertDstIsImmutable(loop {});
257 u.0
258 }
259 } else {
260 use $crate::util::macro_util::TransmuteRefDst;
261 let t = $crate::util::macro_util::Wrap::new(e);
262 // SAFETY: The `if false` branch ensures that:
263 // - `Src: IntoBytes + Immutable`
264 // - `Dst: FromBytes + Immutable`
265 unsafe {
266 t.transmute_ref()
267 }
268 }
269 }}
270}
271
272/// Safely transmutes a mutable reference of one type to a mutable reference of
273/// another type of the same size and compatible alignment.
274///
275/// This macro behaves like an invocation of this function:
276///
277/// ```ignore
278/// const fn transmute_mut<'src, 'dst, Src, Dst>(src: &'src mut Src) -> &'dst mut Dst
279/// where
280/// 'src: 'dst,
281/// Src: FromBytes + IntoBytes,
282/// Dst: FromBytes + IntoBytes,
283/// align_of::<Src>() >= align_of::<Dst>(),
284/// size_compatible::<Src, Dst>(),
285/// {
286/// # /*
287/// ...
288/// # */
289/// }
290/// ```
291///
292/// The types `Src` and `Dst` are inferred from the calling context; they cannot
293/// be explicitly specified in the macro invocation.
294///
295/// # Size compatibility
296///
297/// `transmute_mut!` supports transmuting between `Sized` types or between
298/// unsized (i.e., `?Sized`) types. It supports any transmutation that preserves
299/// the number of bytes of the referent, even if doing so requires updating the
300/// metadata stored in an unsized "fat" reference:
301///
302/// ```
303/// # use zerocopy::transmute_mut;
304/// # use core::mem::size_of_val; // Not in the prelude on our MSRV
305/// let src: &mut [[u8; 2]] = &mut [[0, 1], [2, 3]][..];
306/// let dst: &mut [u8] = transmute_mut!(src);
307///
308/// assert_eq!(dst.len(), 4);
309/// assert_eq!(dst, [0, 1, 2, 3]);
310/// let dst_size = size_of_val(dst);
311/// assert_eq!(src.len(), 2);
312/// assert_eq!(size_of_val(src), dst_size);
313/// ```
314///
315/// # Errors
316///
317/// Violations of the alignment and size compatibility checks are detected
318/// *after* the compiler performs monomorphization. This has two important
319/// consequences.
320///
321/// First, it means that generic code will *never* fail these conditions:
322///
323/// ```
324/// # use zerocopy::{transmute_mut, FromBytes, IntoBytes, Immutable};
325/// fn transmute_mut<Src, Dst>(src: &mut Src) -> &mut Dst
326/// where
327/// Src: FromBytes + IntoBytes,
328/// Dst: FromBytes + IntoBytes,
329/// {
330/// transmute_mut!(src)
331/// }
332/// ```
333///
334/// Instead, failures will only be detected once generic code is instantiated
335/// with concrete types:
336///
337/// ```compile_fail,E0080
338/// # use zerocopy::{transmute_mut, FromBytes, IntoBytes, Immutable};
339/// #
340/// # fn transmute_mut<Src, Dst>(src: &mut Src) -> &mut Dst
341/// # where
342/// # Src: FromBytes + IntoBytes,
343/// # Dst: FromBytes + IntoBytes,
344/// # {
345/// # transmute_mut!(src)
346/// # }
347/// let src: &mut u16 = &mut 0;
348/// let dst: &mut u8 = transmute_mut(src);
349/// ```
350///
351/// Second, the fact that violations are detected after monomorphization means
352/// that `cargo check` will usually not detect errors, even when types are
353/// concrete. Instead, `cargo build` must be used to detect such errors.
354///
355///
356/// # Examples
357///
358/// Transmuting between `Sized` types:
359///
360/// ```
361/// # use zerocopy::transmute_mut;
362/// let mut one_dimensional: [u8; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
363///
364/// let two_dimensional: &mut [[u8; 4]; 2] = transmute_mut!(&mut one_dimensional);
365///
366/// assert_eq!(two_dimensional, &[[0, 1, 2, 3], [4, 5, 6, 7]]);
367///
368/// two_dimensional.reverse();
369///
370/// assert_eq!(one_dimensional, [4, 5, 6, 7, 0, 1, 2, 3]);
371/// ```
372///
373/// Transmuting between unsized types:
374///
375/// ```
376/// # use {zerocopy::*, zerocopy_derive::*};
377/// # type u16 = zerocopy::byteorder::native_endian::U16;
378/// # type u32 = zerocopy::byteorder::native_endian::U32;
379/// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
380/// #[repr(C)]
381/// struct SliceDst<T, U> {
382/// t: T,
383/// u: [U],
384/// }
385///
386/// type Src = SliceDst<u32, u16>;
387/// type Dst = SliceDst<u16, u8>;
388///
389/// let mut bytes = [0, 1, 2, 3, 4, 5, 6, 7];
390/// let src = Src::mut_from_bytes(&mut bytes[..]).unwrap();
391/// let dst: &mut Dst = transmute_mut!(src);
392///
393/// assert_eq!(dst.t.as_bytes(), [0, 1]);
394/// assert_eq!(dst.u, [2, 3, 4, 5, 6, 7]);
395///
396/// assert_eq!(src.t.as_bytes(), [0, 1, 2, 3]);
397/// assert_eq!(src.u.len(), 2);
398/// assert_eq!(src.u.as_bytes(), [4, 5, 6, 7]);
399///
400/// ```
401#[macro_export]
402macro_rules! transmute_mut {
403 ($e:expr) => {{
404 // NOTE: This must be a macro (rather than a function with trait bounds)
405 // because, for backwards-compatibility on v0.8.x, we use the autoref
406 // specialization trick to dispatch to different `transmute_mut`
407 // implementations: one which doesn't require `Src: KnownLayout + Dst:
408 // KnownLayout` when `Src: Sized + Dst: Sized`, and one which requires
409 // `KnownLayout` bounds otherwise.
410
411 // Ensure that the source type is a mutable reference.
412 let e: &mut _ = $e;
413
414 #[allow(unused)]
415 use $crate::util::macro_util::TransmuteMutDst as _;
416 let t = $crate::util::macro_util::Wrap::new(e);
417 t.transmute_mut()
418 }}
419}
420
421/// Conditionally transmutes a value of one type to a value of another type of
422/// the same size.
423///
424/// This macro behaves like an invocation of this function:
425///
426/// ```ignore
427/// fn try_transmute<Src, Dst>(src: Src) -> Result<Dst, ValidityError<Src, Dst>>
428/// where
429/// Src: IntoBytes,
430/// Dst: TryFromBytes,
431/// size_of::<Src>() == size_of::<Dst>(),
432/// {
433/// # /*
434/// ...
435/// # */
436/// }
437/// ```
438///
439/// However, unlike a function, this macro can only be invoked when the types of
440/// `Src` and `Dst` are completely concrete. The types `Src` and `Dst` are
441/// inferred from the calling context; they cannot be explicitly specified in
442/// the macro invocation.
443///
444/// Note that the `Src` produced by the expression `$e` will *not* be dropped.
445/// Semantically, its bits will be copied into a new value of type `Dst`, the
446/// original `Src` will be forgotten, and the value of type `Dst` will be
447/// returned.
448///
449/// # Examples
450///
451/// ```
452/// # use zerocopy::*;
453/// // 0u8 → bool = false
454/// assert_eq!(try_transmute!(0u8), Ok(false));
455///
456/// // 1u8 → bool = true
457/// assert_eq!(try_transmute!(1u8), Ok(true));
458///
459/// // 2u8 → bool = error
460/// assert!(matches!(
461/// try_transmute!(2u8),
462/// Result::<bool, _>::Err(ValidityError { .. })
463/// ));
464/// ```
465#[macro_export]
466macro_rules! try_transmute {
467 ($e:expr) => {{
468 // NOTE: This must be a macro (rather than a function with trait bounds)
469 // because there's no way, in a generic context, to enforce that two
470 // types have the same size. `core::mem::transmute` uses compiler magic
471 // to enforce this so long as the types are concrete.
472
473 let e = $e;
474 if false {
475 // Check that the sizes of the source and destination types are
476 // equal.
477
478 // SAFETY: This code is never executed.
479 Ok(unsafe {
480 // Clippy: We can't annotate the types; this macro is designed
481 // to infer the types from the calling context.
482 #[allow(clippy::missing_transmute_annotations)]
483 $crate::util::macro_util::core_reexport::mem::transmute(e)
484 })
485 } else {
486 $crate::util::macro_util::try_transmute::<_, _>(e)
487 }
488 }}
489}
490
491/// Conditionally transmutes a mutable or immutable reference of one type to an
492/// immutable reference of another type of the same size and compatible
493/// alignment.
494///
495/// This macro behaves like an invocation of this function:
496///
497/// ```ignore
498/// fn try_transmute_ref<Src, Dst>(src: &Src) -> Result<&Dst, ValidityError<&Src, Dst>>
499/// where
500/// Src: IntoBytes + Immutable,
501/// Dst: TryFromBytes + Immutable,
502/// size_of::<Src>() == size_of::<Dst>(),
503/// align_of::<Src>() >= align_of::<Dst>(),
504/// {
505/// # /*
506/// ...
507/// # */
508/// }
509/// ```
510///
511/// However, unlike a function, this macro can only be invoked when the types of
512/// `Src` and `Dst` are completely concrete. The types `Src` and `Dst` are
513/// inferred from the calling context; they cannot be explicitly specified in
514/// the macro invocation.
515///
516/// # Examples
517///
518/// ```
519/// # use zerocopy::*;
520/// // 0u8 → bool = false
521/// assert_eq!(try_transmute_ref!(&0u8), Ok(&false));
522///
523/// // 1u8 → bool = true
524/// assert_eq!(try_transmute_ref!(&1u8), Ok(&true));
525///
526/// // 2u8 → bool = error
527/// assert!(matches!(
528/// try_transmute_ref!(&2u8),
529/// Result::<&bool, _>::Err(ValidityError { .. })
530/// ));
531/// ```
532///
533/// # Alignment increase error message
534///
535/// Because of limitations on macros, the error message generated when
536/// `try_transmute_ref!` is used to transmute from a type of lower alignment to
537/// a type of higher alignment is somewhat confusing. For example, the following
538/// code:
539///
540/// ```compile_fail
541/// let increase_alignment: Result<&u16, _> = zerocopy::try_transmute_ref!(&[0u8; 2]);
542/// ```
543///
544/// ...generates the following error:
545///
546/// ```text
547/// error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
548/// --> example.rs:1:47
549/// |
550/// 1 | let increase_alignment: Result<&u16, _> = zerocopy::try_transmute_ref!(&[0u8; 2]);
551/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
552/// |
553/// = note: source type: `AlignOf<[u8; 2]>` (8 bits)
554/// = note: target type: `MaxAlignsOf<[u8; 2], u16>` (16 bits)
555/// = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `zerocopy::try_transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)/// ```
556/// ```
557///
558/// This is saying that `max(align_of::<T>(), align_of::<U>()) !=
559/// align_of::<T>()`, which is equivalent to `align_of::<T>() <
560/// align_of::<U>()`.
561#[macro_export]
562macro_rules! try_transmute_ref {
563 ($e:expr) => {{
564 // NOTE: This must be a macro (rather than a function with trait bounds)
565 // because there's no way, in a generic context, to enforce that two
566 // types have the same size. `core::mem::transmute` uses compiler magic
567 // to enforce this so long as the types are concrete.
568
569 // Ensure that the source type is a reference or a mutable reference
570 // (note that mutable references are implicitly reborrowed here).
571 let e: &_ = $e;
572
573 #[allow(unreachable_code, unused, clippy::diverging_sub_expression)]
574 if false {
575 // This branch, though never taken, ensures that `size_of::<T>() ==
576 // size_of::<U>()` and that that `align_of::<T>() >=
577 // align_of::<U>()`.
578
579 // `t` is inferred to have type `T` because it's assigned to `e` (of
580 // type `&T`) as `&t`.
581 let mut t = loop {};
582 e = &t;
583
584 // `u` is inferred to have type `U` because it's used as `Ok(&u)` as
585 // the value returned from this branch.
586 let u;
587
588 $crate::assert_size_eq!(t, u);
589 $crate::assert_align_gt_eq!(t, u);
590
591 Ok(&u)
592 } else {
593 $crate::util::macro_util::try_transmute_ref::<_, _>(e)
594 }
595 }}
596}
597
598/// Conditionally transmutes a mutable reference of one type to a mutable
599/// reference of another type of the same size and compatible alignment.
600///
601/// This macro behaves like an invocation of this function:
602///
603/// ```ignore
604/// fn try_transmute_mut<Src, Dst>(src: &mut Src) -> Result<&mut Dst, ValidityError<&mut Src, Dst>>
605/// where
606/// Src: FromBytes + IntoBytes,
607/// Dst: TryFromBytes + IntoBytes,
608/// size_of::<Src>() == size_of::<Dst>(),
609/// align_of::<Src>() >= align_of::<Dst>(),
610/// {
611/// # /*
612/// ...
613/// # */
614/// }
615/// ```
616///
617/// However, unlike a function, this macro can only be invoked when the types of
618/// `Src` and `Dst` are completely concrete. The types `Src` and `Dst` are
619/// inferred from the calling context; they cannot be explicitly specified in
620/// the macro invocation.
621///
622/// # Examples
623///
624/// ```
625/// # use zerocopy::*;
626/// // 0u8 → bool = false
627/// let src = &mut 0u8;
628/// assert_eq!(try_transmute_mut!(src), Ok(&mut false));
629///
630/// // 1u8 → bool = true
631/// let src = &mut 1u8;
632/// assert_eq!(try_transmute_mut!(src), Ok(&mut true));
633///
634/// // 2u8 → bool = error
635/// let src = &mut 2u8;
636/// assert!(matches!(
637/// try_transmute_mut!(src),
638/// Result::<&mut bool, _>::Err(ValidityError { .. })
639/// ));
640/// ```
641///
642/// # Alignment increase error message
643///
644/// Because of limitations on macros, the error message generated when
645/// `try_transmute_ref!` is used to transmute from a type of lower alignment to
646/// a type of higher alignment is somewhat confusing. For example, the following
647/// code:
648///
649/// ```compile_fail
650/// let src = &mut [0u8; 2];
651/// let increase_alignment: Result<&mut u16, _> = zerocopy::try_transmute_mut!(src);
652/// ```
653///
654/// ...generates the following error:
655///
656/// ```text
657/// error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
658/// --> example.rs:2:51
659/// |
660/// 2 | let increase_alignment: Result<&mut u16, _> = zerocopy::try_transmute_mut!(src);
661/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
662/// |
663/// = note: source type: `AlignOf<[u8; 2]>` (8 bits)
664/// = note: target type: `MaxAlignsOf<[u8; 2], u16>` (16 bits)
665/// = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `zerocopy::try_transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
666/// ```
667///
668/// This is saying that `max(align_of::<T>(), align_of::<U>()) !=
669/// align_of::<T>()`, which is equivalent to `align_of::<T>() <
670/// align_of::<U>()`.
671#[macro_export]
672macro_rules! try_transmute_mut {
673 ($e:expr) => {{
674 // NOTE: This must be a macro (rather than a function with trait bounds)
675 // because there's no way, in a generic context, to enforce that two
676 // types have the same size. `core::mem::transmute` uses compiler magic
677 // to enforce this so long as the types are concrete.
678
679 // Ensure that the source type is a mutable reference.
680 let e: &mut _ = $e;
681
682 #[allow(unreachable_code, unused, clippy::diverging_sub_expression)]
683 if false {
684 // This branch, though never taken, ensures that `size_of::<T>() ==
685 // size_of::<U>()` and that that `align_of::<T>() >=
686 // align_of::<U>()`.
687
688 // `t` is inferred to have type `T` because it's assigned to `e` (of
689 // type `&mut T`) as `&mut t`.
690 let mut t = loop {};
691 e = &mut t;
692
693 // `u` is inferred to have type `U` because it's used as `Ok(&mut
694 // u)` as the value returned from this branch.
695 let u;
696
697 $crate::assert_size_eq!(t, u);
698 $crate::assert_align_gt_eq!(t, u);
699
700 Ok(&mut u)
701 } else {
702 $crate::util::macro_util::try_transmute_mut::<_, _>(e)
703 }
704 }}
705}
706
707/// Includes a file and safely transmutes it to a value of an arbitrary type.
708///
709/// The file will be included as a byte array, `[u8; N]`, which will be
710/// transmuted to another type, `T`. `T` is inferred from the calling context,
711/// and must implement [`FromBytes`].
712///
713/// The file is located relative to the current file (similarly to how modules
714/// are found). The provided path is interpreted in a platform-specific way at
715/// compile time. So, for instance, an invocation with a Windows path containing
716/// backslashes `\` would not compile correctly on Unix.
717///
718/// `include_value!` is ignorant of byte order. For byte order-aware types, see
719/// the [`byteorder`] module.
720///
721/// [`FromBytes`]: crate::FromBytes
722/// [`byteorder`]: crate::byteorder
723///
724/// # Examples
725///
726/// Assume there are two files in the same directory with the following
727/// contents:
728///
729/// File `data` (no trailing newline):
730///
731/// ```text
732/// abcd
733/// ```
734///
735/// File `main.rs`:
736///
737/// ```rust
738/// use zerocopy::include_value;
739/// # macro_rules! include_value {
740/// # ($file:expr) => { zerocopy::include_value!(concat!("../testdata/include_value/", $file)) };
741/// # }
742///
743/// fn main() {
744/// let as_u32: u32 = include_value!("data");
745/// assert_eq!(as_u32, u32::from_ne_bytes([b'a', b'b', b'c', b'd']));
746/// let as_i32: i32 = include_value!("data");
747/// assert_eq!(as_i32, i32::from_ne_bytes([b'a', b'b', b'c', b'd']));
748/// }
749/// ```
750///
751/// # Use in `const` contexts
752///
753/// This macro can be invoked in `const` contexts.
754#[doc(alias("include_bytes", "include_data", "include_type"))]
755#[macro_export]
756macro_rules! include_value {
757 ($file:expr $(,)?) => {
758 $crate::transmute!(*::core::include_bytes!($file))
759 };
760}
761
762#[doc(hidden)]
763#[macro_export]
764macro_rules! cryptocorrosion_derive_traits {
765 (
766 #[repr($repr:ident)]
767 $(#[$attr:meta])*
768 $vis:vis struct $name:ident $(<$($tyvar:ident),*>)?
769 $(
770 (
771 $($tuple_field_vis:vis $tuple_field_ty:ty),*
772 );
773 )?
774
775 $(
776 {
777 $($field_vis:vis $field_name:ident: $field_ty:ty,)*
778 }
779 )?
780 ) => {
781 $crate::cryptocorrosion_derive_traits!(@assert_allowed_struct_repr #[repr($repr)]);
782
783 $(#[$attr])*
784 #[repr($repr)]
785 $vis struct $name $(<$($tyvar),*>)?
786 $(
787 (
788 $($tuple_field_vis $tuple_field_ty),*
789 );
790 )?
791
792 $(
793 {
794 $($field_vis $field_name: $field_ty,)*
795 }
796 )?
797
798 // SAFETY: See inline.
799 unsafe impl $(<$($tyvar),*>)? $crate::TryFromBytes for $name$(<$($tyvar),*>)?
800 where
801 $(
802 $($tuple_field_ty: $crate::FromBytes,)*
803 )?
804
805 $(
806 $($field_ty: $crate::FromBytes,)*
807 )?
808 {
809 fn is_bit_valid<A>(_c: $crate::Maybe<'_, Self, A>) -> bool
810 where
811 A: $crate::pointer::invariant::Reference
812 {
813 // SAFETY: This macro only accepts `#[repr(C)]` and
814 // `#[repr(transparent)]` structs, and this `impl` block
815 // requires all field types to be `FromBytes`. Thus, all
816 // initialized byte sequences constitutes valid instances of
817 // `Self`.
818 true
819 }
820
821 fn only_derive_is_allowed_to_implement_this_trait() {}
822 }
823
824 // SAFETY: This macro only accepts `#[repr(C)]` and
825 // `#[repr(transparent)]` structs, and this `impl` block requires all
826 // field types to be `FromBytes`, which is a sub-trait of `FromZeros`.
827 unsafe impl $(<$($tyvar),*>)? $crate::FromZeros for $name$(<$($tyvar),*>)?
828 where
829 $(
830 $($tuple_field_ty: $crate::FromBytes,)*
831 )?
832
833 $(
834 $($field_ty: $crate::FromBytes,)*
835 )?
836 {
837 fn only_derive_is_allowed_to_implement_this_trait() {}
838 }
839
840 // SAFETY: This macro only accepts `#[repr(C)]` and
841 // `#[repr(transparent)]` structs, and this `impl` block requires all
842 // field types to be `FromBytes`.
843 unsafe impl $(<$($tyvar),*>)? $crate::FromBytes for $name$(<$($tyvar),*>)?
844 where
845 $(
846 $($tuple_field_ty: $crate::FromBytes,)*
847 )?
848
849 $(
850 $($field_ty: $crate::FromBytes,)*
851 )?
852 {
853 fn only_derive_is_allowed_to_implement_this_trait() {}
854 }
855
856 // SAFETY: This macro only accepts `#[repr(C)]` and
857 // `#[repr(transparent)]` structs, this `impl` block requires all field
858 // types to be `IntoBytes`, and a padding check is used to ensures that
859 // there are no padding bytes.
860 unsafe impl $(<$($tyvar),*>)? $crate::IntoBytes for $name$(<$($tyvar),*>)?
861 where
862 $(
863 $($tuple_field_ty: $crate::IntoBytes,)*
864 )?
865
866 $(
867 $($field_ty: $crate::IntoBytes,)*
868 )?
869
870 (): $crate::util::macro_util::PaddingFree<
871 Self,
872 {
873 $crate::cryptocorrosion_derive_traits!(
874 @struct_padding_check #[repr($repr)]
875 $(($($tuple_field_ty),*))?
876 $({$($field_ty),*})?
877 )
878 },
879 >,
880 {
881 fn only_derive_is_allowed_to_implement_this_trait() {}
882 }
883
884 // SAFETY: This macro only accepts `#[repr(C)]` and
885 // `#[repr(transparent)]` structs, and this `impl` block requires all
886 // field types to be `Immutable`.
887 unsafe impl $(<$($tyvar),*>)? $crate::Immutable for $name$(<$($tyvar),*>)?
888 where
889 $(
890 $($tuple_field_ty: $crate::Immutable,)*
891 )?
892
893 $(
894 $($field_ty: $crate::Immutable,)*
895 )?
896 {
897 fn only_derive_is_allowed_to_implement_this_trait() {}
898 }
899 };
900 (@assert_allowed_struct_repr #[repr(transparent)]) => {};
901 (@assert_allowed_struct_repr #[repr(C)]) => {};
902 (@assert_allowed_struct_repr #[$_attr:meta]) => {
903 compile_error!("repr must be `#[repr(transparent)]` or `#[repr(C)]`");
904 };
905 (
906 @struct_padding_check #[repr(transparent)]
907 $(($($tuple_field_ty:ty),*))?
908 $({$($field_ty:ty),*})?
909 ) => {
910 // SAFETY: `#[repr(transparent)]` structs cannot have the same layout as
911 // their single non-zero-sized field, and so cannot have any padding
912 // outside of that field.
913 false
914 };
915 (
916 @struct_padding_check #[repr(C)]
917 $(($($tuple_field_ty:ty),*))?
918 $({$($field_ty:ty),*})?
919 ) => {
920 $crate::struct_has_padding!(
921 Self,
922 [
923 $($($tuple_field_ty),*)?
924 $($($field_ty),*)?
925 ]
926 )
927 };
928 (
929 #[repr(C)]
930 $(#[$attr:meta])*
931 $vis:vis union $name:ident {
932 $(
933 $field_name:ident: $field_ty:ty,
934 )*
935 }
936 ) => {
937 $(#[$attr])*
938 #[repr(C)]
939 $vis union $name {
940 $(
941 $field_name: $field_ty,
942 )*
943 }
944
945 // SAFETY: See inline.
946 unsafe impl $crate::TryFromBytes for $name
947 where
948 $(
949 $field_ty: $crate::FromBytes,
950 )*
951 {
952 fn is_bit_valid<A>(_c: $crate::Maybe<'_, Self, A>) -> bool
953 where
954 A: $crate::pointer::invariant::Reference
955 {
956 // SAFETY: This macro only accepts `#[repr(C)]` unions, and this
957 // `impl` block requires all field types to be `FromBytes`.
958 // Thus, all initialized byte sequences constitutes valid
959 // instances of `Self`.
960 true
961 }
962
963 fn only_derive_is_allowed_to_implement_this_trait() {}
964 }
965
966 // SAFETY: This macro only accepts `#[repr(C)]` unions, and this `impl`
967 // block requires all field types to be `FromBytes`, which is a
968 // sub-trait of `FromZeros`.
969 unsafe impl $crate::FromZeros for $name
970 where
971 $(
972 $field_ty: $crate::FromBytes,
973 )*
974 {
975 fn only_derive_is_allowed_to_implement_this_trait() {}
976 }
977
978 // SAFETY: This macro only accepts `#[repr(C)]` unions, and this `impl`
979 // block requires all field types to be `FromBytes`.
980 unsafe impl $crate::FromBytes for $name
981 where
982 $(
983 $field_ty: $crate::FromBytes,
984 )*
985 {
986 fn only_derive_is_allowed_to_implement_this_trait() {}
987 }
988
989 // SAFETY: This macro only accepts `#[repr(C)]` unions, this `impl`
990 // block requires all field types to be `IntoBytes`, and a padding check
991 // is used to ensures that there are no padding bytes before or after
992 // any field.
993 unsafe impl $crate::IntoBytes for $name
994 where
995 $(
996 $field_ty: $crate::IntoBytes,
997 )*
998 (): $crate::util::macro_util::PaddingFree<
999 Self,
1000 {
1001 $crate::union_has_padding!(
1002 Self,
1003 [$($field_ty),*]
1004 )
1005 },
1006 >,
1007 {
1008 fn only_derive_is_allowed_to_implement_this_trait() {}
1009 }
1010
1011 // SAFETY: This macro only accepts `#[repr(C)]` unions, and this `impl`
1012 // block requires all field types to be `Immutable`.
1013 unsafe impl $crate::Immutable for $name
1014 where
1015 $(
1016 $field_ty: $crate::Immutable,
1017 )*
1018 {
1019 fn only_derive_is_allowed_to_implement_this_trait() {}
1020 }
1021 };
1022}
1023
1024#[cfg(test)]
1025mod tests {
1026 use crate::*;
1027 use crate::{
1028 byteorder::native_endian::{U16, U32},
1029 util::testutil::*,
1030 };
1031
1032 #[derive(KnownLayout, Immutable, FromBytes, IntoBytes, PartialEq, Debug)]
1033 #[repr(C)]
1034 struct SliceDst<T, U> {
1035 a: T,
1036 b: [U],
1037 }
1038
1039 #[test]
1040 fn test_transmute() {
1041 // Test that memory is transmuted as expected.
1042 let array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
1043 let array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
1044 let x: [[u8; 2]; 4] = transmute!(array_of_u8s);
1045 assert_eq!(x, array_of_arrays);
1046 let x: [u8; 8] = transmute!(array_of_arrays);
1047 assert_eq!(x, array_of_u8s);
1048
1049 // Test that the source expression's value is forgotten rather than
1050 // dropped.
1051 #[derive(IntoBytes)]
1052 #[repr(transparent)]
1053 struct PanicOnDrop(());
1054 impl Drop for PanicOnDrop {
1055 fn drop(&mut self) {
1056 panic!("PanicOnDrop::drop");
1057 }
1058 }
1059 #[allow(clippy::let_unit_value)]
1060 let _: () = transmute!(PanicOnDrop(()));
1061
1062 // Test that `transmute!` is legal in a const context.
1063 const ARRAY_OF_U8S: [u8; 8] = [0u8, 1, 2, 3, 4, 5, 6, 7];
1064 const ARRAY_OF_ARRAYS: [[u8; 2]; 4] = [[0, 1], [2, 3], [4, 5], [6, 7]];
1065 const X: [[u8; 2]; 4] = transmute!(ARRAY_OF_U8S);
1066 assert_eq!(X, ARRAY_OF_ARRAYS);
1067
1068 // Test that `transmute!` works with `!Immutable` types.
1069 let x: usize = transmute!(UnsafeCell::new(1usize));
1070 assert_eq!(x, 1);
1071 let x: UnsafeCell<usize> = transmute!(1usize);
1072 assert_eq!(x.into_inner(), 1);
1073 let x: UnsafeCell<isize> = transmute!(UnsafeCell::new(1usize));
1074 assert_eq!(x.into_inner(), 1);
1075 }
1076
1077 // A `Sized` type which doesn't implement `KnownLayout` (it is "not
1078 // `KnownLayout`", or `Nkl`).
1079 //
1080 // This permits us to test that `transmute_ref!` and `transmute_mut!` work
1081 // for types which are `Sized + !KnownLayout`. When we added support for
1082 // slice DSTs in #1924, this new support relied on `KnownLayout`, but we
1083 // need to make sure to remain backwards-compatible with code which ueses
1084 // these macros with types which are `!KnownLayout`.
1085 #[derive(FromBytes, IntoBytes, Immutable, PartialEq, Eq, Debug)]
1086 #[repr(transparent)]
1087 struct Nkl<T>(T);
1088
1089 #[test]
1090 fn test_transmute_ref() {
1091 // Test that memory is transmuted as expected.
1092 let array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
1093 let array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
1094 let x: &[[u8; 2]; 4] = transmute_ref!(&array_of_u8s);
1095 assert_eq!(*x, array_of_arrays);
1096 let x: &[u8; 8] = transmute_ref!(&array_of_arrays);
1097 assert_eq!(*x, array_of_u8s);
1098
1099 // Test that `transmute_ref!` is legal in a const context.
1100 const ARRAY_OF_U8S: [u8; 8] = [0u8, 1, 2, 3, 4, 5, 6, 7];
1101 const ARRAY_OF_ARRAYS: [[u8; 2]; 4] = [[0, 1], [2, 3], [4, 5], [6, 7]];
1102 #[allow(clippy::redundant_static_lifetimes)]
1103 const X: &'static [[u8; 2]; 4] = transmute_ref!(&ARRAY_OF_U8S);
1104 assert_eq!(*X, ARRAY_OF_ARRAYS);
1105
1106 // Before 1.61.0, we can't define the `const fn transmute_ref` function
1107 // that we do on and after 1.61.0.
1108 #[cfg(not(zerocopy_generic_bounds_in_const_fn_1_61_0))]
1109 {
1110 // Test that `transmute_ref!` supports non-`KnownLayout` `Sized` types.
1111 const ARRAY_OF_NKL_U8S: Nkl<[u8; 8]> = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
1112 const ARRAY_OF_NKL_ARRAYS: Nkl<[[u8; 2]; 4]> = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
1113 const X_NKL: &Nkl<[[u8; 2]; 4]> = transmute_ref!(&ARRAY_OF_NKL_U8S);
1114 assert_eq!(*X_NKL, ARRAY_OF_NKL_ARRAYS);
1115 }
1116
1117 #[cfg(zerocopy_generic_bounds_in_const_fn_1_61_0)]
1118 {
1119 // Call through a generic function to make sure our autoref
1120 // specialization trick works even when types are generic.
1121 const fn transmute_ref<T, U>(t: &T) -> &U
1122 where
1123 T: IntoBytes + Immutable,
1124 U: FromBytes + Immutable,
1125 {
1126 transmute_ref!(t)
1127 }
1128
1129 // Test that `transmute_ref!` supports non-`KnownLayout` `Sized` types.
1130 const ARRAY_OF_NKL_U8S: Nkl<[u8; 8]> = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
1131 const ARRAY_OF_NKL_ARRAYS: Nkl<[[u8; 2]; 4]> = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
1132 const X_NKL: &Nkl<[[u8; 2]; 4]> = transmute_ref(&ARRAY_OF_NKL_U8S);
1133 assert_eq!(*X_NKL, ARRAY_OF_NKL_ARRAYS);
1134 }
1135
1136 // Test that `transmute_ref!` works on slice DSTs in and that memory is
1137 // transmuted as expected.
1138 let slice_dst_of_u8s =
1139 SliceDst::<U16, [u8; 2]>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
1140 let slice_dst_of_u16s =
1141 SliceDst::<U16, U16>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
1142 let x: &SliceDst<U16, U16> = transmute_ref!(slice_dst_of_u8s);
1143 assert_eq!(x, slice_dst_of_u16s);
1144
1145 let slice_dst_of_u8s =
1146 SliceDst::<U16, u8>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
1147 let x: &[u8] = transmute_ref!(slice_dst_of_u8s);
1148 assert_eq!(x, [0, 1, 2, 3, 4, 5]);
1149
1150 let x: &[u8] = transmute_ref!(slice_dst_of_u16s);
1151 assert_eq!(x, [0, 1, 2, 3, 4, 5]);
1152
1153 let x: &[U16] = transmute_ref!(slice_dst_of_u16s);
1154 let slice_of_u16s: &[U16] = <[U16]>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
1155 assert_eq!(x, slice_of_u16s);
1156
1157 // Test that transmuting from a type with larger trailing slice offset
1158 // and larger trailing slice element works.
1159 let bytes = &[0, 1, 2, 3, 4, 5, 6, 7][..];
1160 let slice_dst_big = SliceDst::<U32, U16>::ref_from_bytes(bytes).unwrap();
1161 let slice_dst_small = SliceDst::<U16, u8>::ref_from_bytes(bytes).unwrap();
1162 let x: &SliceDst<U16, u8> = transmute_ref!(slice_dst_big);
1163 assert_eq!(x, slice_dst_small);
1164
1165 // Test that it's legal to transmute a reference while shrinking the
1166 // lifetime (note that `X` has the lifetime `'static`).
1167 let x: &[u8; 8] = transmute_ref!(X);
1168 assert_eq!(*x, ARRAY_OF_U8S);
1169
1170 // Test that `transmute_ref!` supports decreasing alignment.
1171 let u = AU64(0);
1172 let array = [0, 0, 0, 0, 0, 0, 0, 0];
1173 let x: &[u8; 8] = transmute_ref!(&u);
1174 assert_eq!(*x, array);
1175
1176 // Test that a mutable reference can be turned into an immutable one.
1177 let mut x = 0u8;
1178 #[allow(clippy::useless_transmute)]
1179 let y: &u8 = transmute_ref!(&mut x);
1180 assert_eq!(*y, 0);
1181 }
1182
1183 #[test]
1184 fn test_try_transmute() {
1185 // Test that memory is transmuted with `try_transmute` as expected.
1186 let array_of_bools = [false, true, false, true, false, true, false, true];
1187 let array_of_arrays = [[0, 1], [0, 1], [0, 1], [0, 1]];
1188 let x: Result<[[u8; 2]; 4], _> = try_transmute!(array_of_bools);
1189 assert_eq!(x, Ok(array_of_arrays));
1190 let x: Result<[bool; 8], _> = try_transmute!(array_of_arrays);
1191 assert_eq!(x, Ok(array_of_bools));
1192
1193 // Test that `try_transmute!` works with `!Immutable` types.
1194 let x: Result<usize, _> = try_transmute!(UnsafeCell::new(1usize));
1195 assert_eq!(x.unwrap(), 1);
1196 let x: Result<UnsafeCell<usize>, _> = try_transmute!(1usize);
1197 assert_eq!(x.unwrap().into_inner(), 1);
1198 let x: Result<UnsafeCell<isize>, _> = try_transmute!(UnsafeCell::new(1usize));
1199 assert_eq!(x.unwrap().into_inner(), 1);
1200
1201 #[derive(FromBytes, IntoBytes, Debug, PartialEq)]
1202 #[repr(transparent)]
1203 struct PanicOnDrop<T>(T);
1204
1205 impl<T> Drop for PanicOnDrop<T> {
1206 fn drop(&mut self) {
1207 panic!("PanicOnDrop dropped");
1208 }
1209 }
1210
1211 // Since `try_transmute!` semantically moves its argument on failure,
1212 // the `PanicOnDrop` is not dropped, and thus this shouldn't panic.
1213 let x: Result<usize, _> = try_transmute!(PanicOnDrop(1usize));
1214 assert_eq!(x, Ok(1));
1215
1216 // Since `try_transmute!` semantically returns ownership of its argument
1217 // on failure, the `PanicOnDrop` is returned rather than dropped, and
1218 // thus this shouldn't panic.
1219 let y: Result<bool, _> = try_transmute!(PanicOnDrop(2u8));
1220 // We have to use `map_err` instead of comparing against
1221 // `Err(PanicOnDrop(2u8))` because the latter would create and then drop
1222 // its `PanicOnDrop` temporary, which would cause a panic.
1223 assert_eq!(y.as_ref().map_err(|p| &p.src.0), Err::<&bool, _>(&2u8));
1224 mem::forget(y);
1225 }
1226
1227 #[test]
1228 fn test_try_transmute_ref() {
1229 // Test that memory is transmuted with `try_transmute_ref` as expected.
1230 let array_of_bools = &[false, true, false, true, false, true, false, true];
1231 let array_of_arrays = &[[0, 1], [0, 1], [0, 1], [0, 1]];
1232 let x: Result<&[[u8; 2]; 4], _> = try_transmute_ref!(array_of_bools);
1233 assert_eq!(x, Ok(array_of_arrays));
1234 let x: Result<&[bool; 8], _> = try_transmute_ref!(array_of_arrays);
1235 assert_eq!(x, Ok(array_of_bools));
1236
1237 // Test that it's legal to transmute a reference while shrinking the
1238 // lifetime.
1239 {
1240 let x: Result<&[[u8; 2]; 4], _> = try_transmute_ref!(array_of_bools);
1241 assert_eq!(x, Ok(array_of_arrays));
1242 }
1243
1244 // Test that `try_transmute_ref!` supports decreasing alignment.
1245 let u = AU64(0);
1246 let array = [0u8, 0, 0, 0, 0, 0, 0, 0];
1247 let x: Result<&[u8; 8], _> = try_transmute_ref!(&u);
1248 assert_eq!(x, Ok(&array));
1249
1250 // Test that a mutable reference can be turned into an immutable one.
1251 let mut x = 0u8;
1252 #[allow(clippy::useless_transmute)]
1253 let y: Result<&u8, _> = try_transmute_ref!(&mut x);
1254 assert_eq!(y, Ok(&0));
1255 }
1256
1257 #[test]
1258 fn test_try_transmute_mut() {
1259 // Test that memory is transmuted with `try_transmute_mut` as expected.
1260 let array_of_u8s = &mut [0u8, 1, 0, 1, 0, 1, 0, 1];
1261 let array_of_arrays = &mut [[0u8, 1], [0, 1], [0, 1], [0, 1]];
1262 let x: Result<&mut [[u8; 2]; 4], _> = try_transmute_mut!(array_of_u8s);
1263 assert_eq!(x, Ok(array_of_arrays));
1264
1265 let array_of_bools = &mut [false, true, false, true, false, true, false, true];
1266 let array_of_arrays = &mut [[0u8, 1], [0, 1], [0, 1], [0, 1]];
1267 let x: Result<&mut [bool; 8], _> = try_transmute_mut!(array_of_arrays);
1268 assert_eq!(x, Ok(array_of_bools));
1269
1270 // Test that it's legal to transmute a reference while shrinking the
1271 // lifetime.
1272 let array_of_bools = &mut [false, true, false, true, false, true, false, true];
1273 let array_of_arrays = &mut [[0u8, 1], [0, 1], [0, 1], [0, 1]];
1274 {
1275 let x: Result<&mut [bool; 8], _> = try_transmute_mut!(array_of_arrays);
1276 assert_eq!(x, Ok(array_of_bools));
1277 }
1278
1279 // Test that `try_transmute_mut!` supports decreasing alignment.
1280 let u = &mut AU64(0);
1281 let array = &mut [0u8, 0, 0, 0, 0, 0, 0, 0];
1282 let x: Result<&mut [u8; 8], _> = try_transmute_mut!(u);
1283 assert_eq!(x, Ok(array));
1284
1285 // Test that a mutable reference can be turned into an immutable one.
1286 let mut x = 0u8;
1287 #[allow(clippy::useless_transmute)]
1288 let y: Result<&mut u8, _> = try_transmute_mut!(&mut x);
1289 assert_eq!(y, Ok(&mut 0));
1290 }
1291
1292 #[test]
1293 fn test_transmute_mut() {
1294 // Test that memory is transmuted as expected.
1295 let mut array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
1296 let mut array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
1297 let x: &mut [[u8; 2]; 4] = transmute_mut!(&mut array_of_u8s);
1298 assert_eq!(*x, array_of_arrays);
1299 let x: &mut [u8; 8] = transmute_mut!(&mut array_of_arrays);
1300 assert_eq!(*x, array_of_u8s);
1301
1302 {
1303 // Test that it's legal to transmute a reference while shrinking the
1304 // lifetime.
1305 let x: &mut [u8; 8] = transmute_mut!(&mut array_of_arrays);
1306 assert_eq!(*x, array_of_u8s);
1307 }
1308
1309 // Test that `transmute_mut!` supports non-`KnownLayout` types.
1310 let mut array_of_u8s = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
1311 let mut array_of_arrays = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
1312 let x: &mut Nkl<[[u8; 2]; 4]> = transmute_mut!(&mut array_of_u8s);
1313 assert_eq!(*x, array_of_arrays);
1314 let x: &mut Nkl<[u8; 8]> = transmute_mut!(&mut array_of_arrays);
1315 assert_eq!(*x, array_of_u8s);
1316
1317 // Test that `transmute_mut!` supports decreasing alignment.
1318 let mut u = AU64(0);
1319 let array = [0, 0, 0, 0, 0, 0, 0, 0];
1320 let x: &[u8; 8] = transmute_mut!(&mut u);
1321 assert_eq!(*x, array);
1322
1323 // Test that a mutable reference can be turned into an immutable one.
1324 let mut x = 0u8;
1325 #[allow(clippy::useless_transmute)]
1326 let y: &u8 = transmute_mut!(&mut x);
1327 assert_eq!(*y, 0);
1328
1329 // Test that `transmute_mut!` works on slice DSTs in and that memory is
1330 // transmuted as expected.
1331 let mut bytes = [0, 1, 2, 3, 4, 5, 6];
1332 let slice_dst_of_u8s = SliceDst::<u8, [u8; 2]>::mut_from_bytes(&mut bytes[..]).unwrap();
1333 let mut bytes = [0, 1, 2, 3, 4, 5, 6];
1334 let slice_dst_of_u16s = SliceDst::<u8, U16>::mut_from_bytes(&mut bytes[..]).unwrap();
1335 let x: &mut SliceDst<u8, U16> = transmute_mut!(slice_dst_of_u8s);
1336 assert_eq!(x, slice_dst_of_u16s);
1337
1338 // Test that `transmute_mut!` works on slices that memory is transmuted
1339 // as expected.
1340 let array_of_u16s: &mut [u16] = &mut [0u16, 1, 2];
1341 let array_of_i16s: &mut [i16] = &mut [0i16, 1, 2];
1342 let x: &mut [i16] = transmute_mut!(array_of_u16s);
1343 assert_eq!(x, array_of_i16s);
1344
1345 // Test that transmuting from a type with larger trailing slice offset
1346 // and larger trailing slice element works.
1347 let mut bytes = [0, 1, 2, 3, 4, 5, 6, 7];
1348 let slice_dst_big = SliceDst::<U32, U16>::mut_from_bytes(&mut bytes[..]).unwrap();
1349 let mut bytes = [0, 1, 2, 3, 4, 5, 6, 7];
1350 let slice_dst_small = SliceDst::<U16, u8>::mut_from_bytes(&mut bytes[..]).unwrap();
1351 let x: &mut SliceDst<U16, u8> = transmute_mut!(slice_dst_big);
1352 assert_eq!(x, slice_dst_small);
1353 }
1354
1355 #[test]
1356 fn test_macros_evaluate_args_once() {
1357 let mut ctr = 0;
1358 #[allow(clippy::useless_transmute)]
1359 let _: usize = transmute!({
1360 ctr += 1;
1361 0usize
1362 });
1363 assert_eq!(ctr, 1);
1364
1365 let mut ctr = 0;
1366 let _: &usize = transmute_ref!({
1367 ctr += 1;
1368 &0usize
1369 });
1370 assert_eq!(ctr, 1);
1371
1372 let mut ctr: usize = 0;
1373 let _: &mut usize = transmute_mut!({
1374 ctr += 1;
1375 &mut ctr
1376 });
1377 assert_eq!(ctr, 1);
1378
1379 let mut ctr = 0;
1380 #[allow(clippy::useless_transmute)]
1381 let _: usize = try_transmute!({
1382 ctr += 1;
1383 0usize
1384 })
1385 .unwrap();
1386 assert_eq!(ctr, 1);
1387 }
1388
1389 #[test]
1390 fn test_include_value() {
1391 const AS_U32: u32 = include_value!("../testdata/include_value/data");
1392 assert_eq!(AS_U32, u32::from_ne_bytes([b'a', b'b', b'c', b'd']));
1393 const AS_I32: i32 = include_value!("../testdata/include_value/data");
1394 assert_eq!(AS_I32, i32::from_ne_bytes([b'a', b'b', b'c', b'd']));
1395 }
1396
1397 #[test]
1398 #[allow(non_camel_case_types, unreachable_pub, dead_code)]
1399 fn test_cryptocorrosion_derive_traits() {
1400 // Test the set of invocations added in
1401 // https://github.com/cryptocorrosion/cryptocorrosion/pull/85
1402
1403 fn assert_impls<T: FromBytes + IntoBytes + Immutable>() {}
1404
1405 cryptocorrosion_derive_traits! {
1406 #[repr(C)]
1407 #[derive(Clone, Copy)]
1408 pub union vec128_storage {
1409 d: [u32; 4],
1410 q: [u64; 2],
1411 }
1412 }
1413
1414 assert_impls::<vec128_storage>();
1415
1416 cryptocorrosion_derive_traits! {
1417 #[repr(transparent)]
1418 #[derive(Copy, Clone, Debug, PartialEq)]
1419 pub struct u32x4_generic([u32; 4]);
1420 }
1421
1422 assert_impls::<u32x4_generic>();
1423
1424 cryptocorrosion_derive_traits! {
1425 #[repr(transparent)]
1426 #[derive(Copy, Clone, Debug, PartialEq)]
1427 pub struct u64x2_generic([u64; 2]);
1428 }
1429
1430 assert_impls::<u64x2_generic>();
1431
1432 cryptocorrosion_derive_traits! {
1433 #[repr(transparent)]
1434 #[derive(Copy, Clone, Debug, PartialEq)]
1435 pub struct u128x1_generic([u128; 1]);
1436 }
1437
1438 assert_impls::<u128x1_generic>();
1439
1440 cryptocorrosion_derive_traits! {
1441 #[repr(transparent)]
1442 #[derive(Copy, Clone, Default)]
1443 #[allow(non_camel_case_types)]
1444 pub struct x2<W, G>(pub [W; 2], PhantomData<G>);
1445 }
1446
1447 enum NotZerocopy {}
1448 assert_impls::<x2<(), NotZerocopy>>();
1449
1450 cryptocorrosion_derive_traits! {
1451 #[repr(transparent)]
1452 #[derive(Copy, Clone, Default)]
1453 #[allow(non_camel_case_types)]
1454 pub struct x4<W>(pub [W; 4]);
1455 }
1456
1457 assert_impls::<x4<()>>();
1458
1459 #[cfg(feature = "simd")]
1460 #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
1461 {
1462 #[cfg(target_arch = "x86")]
1463 use core::arch::x86::{__m128i, __m256i};
1464 #[cfg(target_arch = "x86_64")]
1465 use core::arch::x86_64::{__m128i, __m256i};
1466
1467 cryptocorrosion_derive_traits! {
1468 #[repr(C)]
1469 #[derive(Copy, Clone)]
1470 pub struct X4(__m128i, __m128i, __m128i, __m128i);
1471 }
1472
1473 assert_impls::<X4>();
1474
1475 cryptocorrosion_derive_traits! {
1476 #[repr(C)]
1477 /// Generic wrapper for unparameterized storage of any of the possible impls.
1478 /// Converting into and out of this type should be essentially free, although it may be more
1479 /// aligned than a particular impl requires.
1480 #[allow(non_camel_case_types)]
1481 #[derive(Copy, Clone)]
1482 pub union vec128_storage {
1483 u32x4: [u32; 4],
1484 u64x2: [u64; 2],
1485 u128x1: [u128; 1],
1486 sse2: __m128i,
1487 }
1488 }
1489
1490 assert_impls::<vec128_storage>();
1491
1492 cryptocorrosion_derive_traits! {
1493 #[repr(transparent)]
1494 #[allow(non_camel_case_types)]
1495 #[derive(Copy, Clone)]
1496 pub struct vec<S3, S4, NI> {
1497 x: __m128i,
1498 s3: PhantomData<S3>,
1499 s4: PhantomData<S4>,
1500 ni: PhantomData<NI>,
1501 }
1502 }
1503
1504 assert_impls::<vec<NotZerocopy, NotZerocopy, NotZerocopy>>();
1505
1506 cryptocorrosion_derive_traits! {
1507 #[repr(transparent)]
1508 #[derive(Copy, Clone)]
1509 pub struct u32x4x2_avx2<NI> {
1510 x: __m256i,
1511 ni: PhantomData<NI>,
1512 }
1513 }
1514
1515 assert_impls::<u32x4x2_avx2<NotZerocopy>>();
1516 }
1517
1518 // Make sure that our derive works for `#[repr(C)]` structs even though
1519 // cryptocorrosion doesn't currently have any.
1520 cryptocorrosion_derive_traits! {
1521 #[repr(C)]
1522 #[derive(Copy, Clone, Debug, PartialEq)]
1523 pub struct ReprC(u8, u8, u16);
1524 }
1525 }
1526}