diff options
| -rw-r--r-- | library/core/src/clone.rs | 127 | ||||
| -rw-r--r-- | library/core/src/clone/uninit.rs | 128 | ||||
| -rw-r--r-- | library/core/tests/clone.rs | 40 | ||||
| -rw-r--r-- | library/std/src/ffi/os_str.rs | 13 | ||||
| -rw-r--r-- | library/std/src/ffi/os_str/tests.rs | 17 | ||||
| -rw-r--r-- | library/std/src/lib.rs | 1 | ||||
| -rw-r--r-- | library/std/src/path.rs | 12 | ||||
| -rw-r--r-- | library/std/src/path/tests.rs | 19 | ||||
| -rw-r--r-- | library/std/src/sys/os_str/bytes.rs | 13 | ||||
| -rw-r--r-- | library/std/src/sys/os_str/wtf8.rs | 13 | ||||
| -rw-r--r-- | library/std/src/sys_common/wtf8.rs | 12 |
11 files changed, 290 insertions, 105 deletions
diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs index 76a89eaaff8..21504630672 100644 --- a/library/core/src/clone.rs +++ b/library/core/src/clone.rs @@ -36,8 +36,7 @@ #![stable(feature = "rust1", since = "1.0.0")] -use crate::mem::{self, MaybeUninit}; -use crate::ptr; +mod uninit; /// A common trait for the ability to explicitly duplicate an object. /// @@ -248,7 +247,7 @@ pub unsafe trait CloneToUninit { /// * `dst` must be properly aligned. /// * `dst` must have the same [pointer metadata] (slice length or `dyn` vtable) as `self`. /// - /// [valid]: ptr#safety + /// [valid]: crate::ptr#safety /// [pointer metadata]: crate::ptr::metadata() /// /// # Panics @@ -272,124 +271,42 @@ pub unsafe trait CloneToUninit { #[unstable(feature = "clone_to_uninit", issue = "126799")] unsafe impl<T: Clone> CloneToUninit for T { - default unsafe fn clone_to_uninit(&self, dst: *mut Self) { - // SAFETY: The safety conditions of clone_to_uninit() are a superset of those of - // ptr::write(). - unsafe { - // We hope the optimizer will figure out to create the cloned value in-place, - // skipping ever storing it on the stack and the copy to the destination. - ptr::write(dst, self.clone()); - } - } -} - -// Specialized implementation for types that are [`Copy`], not just [`Clone`], -// and can therefore be copied bitwise. -#[unstable(feature = "clone_to_uninit", issue = "126799")] -unsafe impl<T: Copy> CloneToUninit for T { + #[inline] unsafe fn clone_to_uninit(&self, dst: *mut Self) { - // SAFETY: The safety conditions of clone_to_uninit() are a superset of those of - // ptr::copy_nonoverlapping(). - unsafe { - ptr::copy_nonoverlapping(self, dst, 1); - } + // SAFETY: we're calling a specialization with the same contract + unsafe { <T as self::uninit::CopySpec>::clone_one(self, dst) } } } #[unstable(feature = "clone_to_uninit", issue = "126799")] unsafe impl<T: Clone> CloneToUninit for [T] { + #[inline] #[cfg_attr(debug_assertions, track_caller)] - default unsafe fn clone_to_uninit(&self, dst: *mut Self) { - let len = self.len(); - // This is the most likely mistake to make, so check it as a debug assertion. - debug_assert_eq!( - len, - dst.len(), - "clone_to_uninit() source and destination must have equal lengths", - ); - - // SAFETY: The produced `&mut` is valid because: - // * The caller is obligated to provide a pointer which is valid for writes. - // * All bytes pointed to are in MaybeUninit, so we don't care about the memory's - // initialization status. - let uninit_ref = unsafe { &mut *(dst as *mut [MaybeUninit<T>]) }; - - // Copy the elements - let mut initializing = InitializingSlice::from_fully_uninit(uninit_ref); - for element_ref in self.iter() { - // If the clone() panics, `initializing` will take care of the cleanup. - initializing.push(element_ref.clone()); - } - // If we reach here, then the entire slice is initialized, and we've satisfied our - // responsibilities to the caller. Disarm the cleanup guard by forgetting it. - mem::forget(initializing); + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: we're calling a specialization with the same contract + unsafe { <T as self::uninit::CopySpec>::clone_slice(self, dst) } } } #[unstable(feature = "clone_to_uninit", issue = "126799")] -unsafe impl<T: Copy> CloneToUninit for [T] { +unsafe impl CloneToUninit for str { + #[inline] #[cfg_attr(debug_assertions, track_caller)] unsafe fn clone_to_uninit(&self, dst: *mut Self) { - let len = self.len(); - // This is the most likely mistake to make, so check it as a debug assertion. - debug_assert_eq!( - len, - dst.len(), - "clone_to_uninit() source and destination must have equal lengths", - ); - - // SAFETY: The safety conditions of clone_to_uninit() are a superset of those of - // ptr::copy_nonoverlapping(). - unsafe { - ptr::copy_nonoverlapping(self.as_ptr(), dst.as_mut_ptr(), len); - } + // SAFETY: str is just a [u8] with UTF-8 invariant + unsafe { self.as_bytes().clone_to_uninit(dst as *mut [u8]) } } } -/// Ownership of a collection of values stored in a non-owned `[MaybeUninit<T>]`, some of which -/// are not yet initialized. This is sort of like a `Vec` that doesn't own its allocation. -/// Its responsibility is to provide cleanup on unwind by dropping the values that *are* -/// initialized, unless disarmed by forgetting. -/// -/// This is a helper for `impl<T: Clone> CloneToUninit for [T]`. -struct InitializingSlice<'a, T> { - data: &'a mut [MaybeUninit<T>], - /// Number of elements of `*self.data` that are initialized. - initialized_len: usize, -} - -impl<'a, T> InitializingSlice<'a, T> { - #[inline] - fn from_fully_uninit(data: &'a mut [MaybeUninit<T>]) -> Self { - Self { data, initialized_len: 0 } - } - - /// Push a value onto the end of the initialized part of the slice. - /// - /// # Panics - /// - /// Panics if the slice is already fully initialized. - #[inline] - fn push(&mut self, value: T) { - MaybeUninit::write(&mut self.data[self.initialized_len], value); - self.initialized_len += 1; - } -} - -impl<'a, T> Drop for InitializingSlice<'a, T> { - #[cold] // will only be invoked on unwind - fn drop(&mut self) { - let initialized_slice = ptr::slice_from_raw_parts_mut( - MaybeUninit::slice_as_mut_ptr(self.data), - self.initialized_len, - ); - // SAFETY: - // * the pointer is valid because it was made from a mutable reference - // * `initialized_len` counts the initialized elements as an invariant of this type, - // so each of the pointed-to elements is initialized and may be dropped. - unsafe { - ptr::drop_in_place::<[T]>(initialized_slice); - } +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for crate::ffi::CStr { + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: For now, CStr is just a #[repr(trasnsparent)] [c_char] with some invariants. + // And we can cast [c_char] to [u8] on all supported platforms (see: to_bytes_with_nul). + // The pointer metadata properly preserves the length (NUL included). + // See: `cstr_metadata_is_length_with_nul` in tests. + unsafe { self.to_bytes_with_nul().clone_to_uninit(dst as *mut [u8]) } } } diff --git a/library/core/src/clone/uninit.rs b/library/core/src/clone/uninit.rs new file mode 100644 index 00000000000..8b738bec796 --- /dev/null +++ b/library/core/src/clone/uninit.rs @@ -0,0 +1,128 @@ +use crate::mem::{self, MaybeUninit}; +use crate::ptr; + +/// Private specialization trait used by CloneToUninit, as per +/// [the dev guide](https://std-dev-guide.rust-lang.org/policy/specialization.html). +pub(super) unsafe trait CopySpec: Clone { + unsafe fn clone_one(src: &Self, dst: *mut Self); + unsafe fn clone_slice(src: &[Self], dst: *mut [Self]); +} + +unsafe impl<T: Clone> CopySpec for T { + #[inline] + default unsafe fn clone_one(src: &Self, dst: *mut Self) { + // SAFETY: The safety conditions of clone_to_uninit() are a superset of those of + // ptr::write(). + unsafe { + // We hope the optimizer will figure out to create the cloned value in-place, + // skipping ever storing it on the stack and the copy to the destination. + ptr::write(dst, src.clone()); + } + } + + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + default unsafe fn clone_slice(src: &[Self], dst: *mut [Self]) { + let len = src.len(); + // This is the most likely mistake to make, so check it as a debug assertion. + debug_assert_eq!( + len, + dst.len(), + "clone_to_uninit() source and destination must have equal lengths", + ); + + // SAFETY: The produced `&mut` is valid because: + // * The caller is obligated to provide a pointer which is valid for writes. + // * All bytes pointed to are in MaybeUninit, so we don't care about the memory's + // initialization status. + let uninit_ref = unsafe { &mut *(dst as *mut [MaybeUninit<T>]) }; + + // Copy the elements + let mut initializing = InitializingSlice::from_fully_uninit(uninit_ref); + for element_ref in src { + // If the clone() panics, `initializing` will take care of the cleanup. + initializing.push(element_ref.clone()); + } + // If we reach here, then the entire slice is initialized, and we've satisfied our + // responsibilities to the caller. Disarm the cleanup guard by forgetting it. + mem::forget(initializing); + } +} + +// Specialized implementation for types that are [`Copy`], not just [`Clone`], +// and can therefore be copied bitwise. +unsafe impl<T: Copy> CopySpec for T { + #[inline] + unsafe fn clone_one(src: &Self, dst: *mut Self) { + // SAFETY: The safety conditions of clone_to_uninit() are a superset of those of + // ptr::copy_nonoverlapping(). + unsafe { + ptr::copy_nonoverlapping(src, dst, 1); + } + } + + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_slice(src: &[Self], dst: *mut [Self]) { + let len = src.len(); + // This is the most likely mistake to make, so check it as a debug assertion. + debug_assert_eq!( + len, + dst.len(), + "clone_to_uninit() source and destination must have equal lengths", + ); + + // SAFETY: The safety conditions of clone_to_uninit() are a superset of those of + // ptr::copy_nonoverlapping(). + unsafe { + ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), len); + } + } +} + +/// Ownership of a collection of values stored in a non-owned `[MaybeUninit<T>]`, some of which +/// are not yet initialized. This is sort of like a `Vec` that doesn't own its allocation. +/// Its responsibility is to provide cleanup on unwind by dropping the values that *are* +/// initialized, unless disarmed by forgetting. +/// +/// This is a helper for `impl<T: Clone> CloneToUninit for [T]`. +struct InitializingSlice<'a, T> { + data: &'a mut [MaybeUninit<T>], + /// Number of elements of `*self.data` that are initialized. + initialized_len: usize, +} + +impl<'a, T> InitializingSlice<'a, T> { + #[inline] + fn from_fully_uninit(data: &'a mut [MaybeUninit<T>]) -> Self { + Self { data, initialized_len: 0 } + } + + /// Push a value onto the end of the initialized part of the slice. + /// + /// # Panics + /// + /// Panics if the slice is already fully initialized. + #[inline] + fn push(&mut self, value: T) { + MaybeUninit::write(&mut self.data[self.initialized_len], value); + self.initialized_len += 1; + } +} + +impl<'a, T> Drop for InitializingSlice<'a, T> { + #[cold] // will only be invoked on unwind + fn drop(&mut self) { + let initialized_slice = ptr::slice_from_raw_parts_mut( + MaybeUninit::slice_as_mut_ptr(self.data), + self.initialized_len, + ); + // SAFETY: + // * the pointer is valid because it was made from a mutable reference + // * `initialized_len` counts the initialized elements as an invariant of this type, + // so each of the pointed-to elements is initialized and may be dropped. + unsafe { + ptr::drop_in_place::<[T]>(initialized_slice); + } + } +} diff --git a/library/core/tests/clone.rs b/library/core/tests/clone.rs index b7130f16f87..71a328733b7 100644 --- a/library/core/tests/clone.rs +++ b/library/core/tests/clone.rs @@ -1,5 +1,7 @@ use core::clone::CloneToUninit; +use core::ffi::CStr; use core::mem::MaybeUninit; +use core::ptr; #[test] #[allow(suspicious_double_ref_op)] @@ -81,3 +83,41 @@ fn test_clone_to_uninit_slice_drops_on_panic() { drop(a); assert_eq!(COUNTER.load(Relaxed), 0); } + +#[test] +fn test_clone_to_uninit_str() { + let a = "hello"; + + let mut storage: MaybeUninit<[u8; 5]> = MaybeUninit::uninit(); + unsafe { a.clone_to_uninit(storage.as_mut_ptr() as *mut [u8] as *mut str) }; + assert_eq!(a.as_bytes(), unsafe { storage.assume_init() }.as_slice()); + + let mut b: Box<str> = "world".into(); + assert_eq!(a.len(), b.len()); + assert_ne!(a, &*b); + unsafe { a.clone_to_uninit(ptr::from_mut::<str>(&mut b)) }; + assert_eq!(a, &*b); +} + +#[test] +fn test_clone_to_uninit_cstr() { + let a = c"hello"; + + let mut storage: MaybeUninit<[u8; 6]> = MaybeUninit::uninit(); + unsafe { a.clone_to_uninit(storage.as_mut_ptr() as *mut [u8] as *mut CStr) }; + assert_eq!(a.to_bytes_with_nul(), unsafe { storage.assume_init() }.as_slice()); + + let mut b: Box<CStr> = c"world".into(); + assert_eq!(a.count_bytes(), b.count_bytes()); + assert_ne!(a, &*b); + unsafe { a.clone_to_uninit(ptr::from_mut::<CStr>(&mut b)) }; + assert_eq!(a, &*b); +} + +#[test] +fn cstr_metadata_is_length_with_nul() { + let s: &CStr = c"abcdef"; + let p: *const CStr = ptr::from_ref(s); + let bytes: *const [u8] = p as *const [u8]; + assert_eq!(s.to_bytes_with_nul().len(), bytes.len()); +} diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs index a501bcc98cf..918eec2d0d8 100644 --- a/library/std/src/ffi/os_str.rs +++ b/library/std/src/ffi/os_str.rs @@ -3,10 +3,13 @@ #[cfg(test)] mod tests; +use core::clone::CloneToUninit; + use crate::borrow::{Borrow, Cow}; use crate::collections::TryReserveError; use crate::hash::{Hash, Hasher}; use crate::ops::{self, Range}; +use crate::ptr::addr_of_mut; use crate::rc::Rc; use crate::str::FromStr; use crate::sync::Arc; @@ -1261,6 +1264,16 @@ impl Clone for Box<OsStr> { } } +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for OsStr { + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: we're just a wrapper around a platform-specific Slice + unsafe { self.inner.clone_to_uninit(addr_of_mut!((*dst).inner)) } + } +} + #[stable(feature = "shared_from_slice2", since = "1.24.0")] impl From<OsString> for Arc<OsStr> { /// Converts an [`OsString`] into an <code>[Arc]<[OsStr]></code> by moving the [`OsString`] diff --git a/library/std/src/ffi/os_str/tests.rs b/library/std/src/ffi/os_str/tests.rs index 5b39b9e34d8..67147934b4d 100644 --- a/library/std/src/ffi/os_str/tests.rs +++ b/library/std/src/ffi/os_str/tests.rs @@ -1,4 +1,6 @@ use super::*; +use crate::mem::MaybeUninit; +use crate::ptr; #[test] fn test_os_string_with_capacity() { @@ -286,3 +288,18 @@ fn slice_surrogate_edge() { assert_eq!(post_crab.slice_encoded_bytes(..4), "🦀"); assert_eq!(post_crab.slice_encoded_bytes(4..), surrogate); } + +#[test] +fn clone_to_uninit() { + let a = OsStr::new("hello.txt"); + + let mut storage = vec![MaybeUninit::<u8>::uninit(); size_of_val::<OsStr>(a)]; + unsafe { a.clone_to_uninit(ptr::from_mut::<[_]>(storage.as_mut_slice()) as *mut OsStr) }; + assert_eq!(a.as_encoded_bytes(), unsafe { MaybeUninit::slice_assume_init_ref(&storage) }); + + let mut b: Box<OsStr> = OsStr::new("world.exe").into(); + assert_eq!(size_of_val::<OsStr>(a), size_of_val::<OsStr>(&b)); + assert_ne!(a, &*b); + unsafe { a.clone_to_uninit(ptr::from_mut::<OsStr>(&mut b)) }; + assert_eq!(a, &*b); +} diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs index 93a74ef739b..2530a376387 100644 --- a/library/std/src/lib.rs +++ b/library/std/src/lib.rs @@ -319,6 +319,7 @@ // tidy-alphabetical-start #![feature(c_str_module)] #![feature(char_internals)] +#![feature(clone_to_uninit)] #![feature(core_intrinsics)] #![feature(core_io_borrowed_buf)] #![feature(duration_constants)] diff --git a/library/std/src/path.rs b/library/std/src/path.rs index 80163667636..9eaa0e01c2c 100644 --- a/library/std/src/path.rs +++ b/library/std/src/path.rs @@ -70,6 +70,8 @@ #[cfg(test)] mod tests; +use core::clone::CloneToUninit; + use crate::borrow::{Borrow, Cow}; use crate::collections::TryReserveError; use crate::error::Error; @@ -3109,6 +3111,16 @@ impl Path { } } +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for Path { + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: Path is just a wrapper around OsStr + unsafe { self.inner.clone_to_uninit(core::ptr::addr_of_mut!((*dst).inner)) } + } +} + #[stable(feature = "rust1", since = "1.0.0")] impl AsRef<OsStr> for Path { #[inline] diff --git a/library/std/src/path/tests.rs b/library/std/src/path/tests.rs index a12e42cba0c..6436872087d 100644 --- a/library/std/src/path/tests.rs +++ b/library/std/src/path/tests.rs @@ -3,6 +3,8 @@ use core::hint::black_box; use super::*; use crate::collections::{BTreeSet, HashSet}; use crate::hash::DefaultHasher; +use crate::mem::MaybeUninit; +use crate::ptr; #[allow(unknown_lints, unused_macro_rules)] macro_rules! t ( @@ -2054,3 +2056,20 @@ fn bench_hash_path_long(b: &mut test::Bencher) { black_box(hasher.finish()); } + +#[test] +fn clone_to_uninit() { + let a = Path::new("hello.txt"); + + let mut storage = vec![MaybeUninit::<u8>::uninit(); size_of_val::<Path>(a)]; + unsafe { a.clone_to_uninit(ptr::from_mut::<[_]>(storage.as_mut_slice()) as *mut Path) }; + assert_eq!(a.as_os_str().as_encoded_bytes(), unsafe { + MaybeUninit::slice_assume_init_ref(&storage) + }); + + let mut b: Box<Path> = Path::new("world.exe").into(); + assert_eq!(size_of_val::<Path>(a), size_of_val::<Path>(&b)); + assert_ne!(a, &*b); + unsafe { a.clone_to_uninit(ptr::from_mut::<Path>(&mut b)) }; + assert_eq!(a, &*b); +} diff --git a/library/std/src/sys/os_str/bytes.rs b/library/std/src/sys/os_str/bytes.rs index 0f8bd645352..992767211d0 100644 --- a/library/std/src/sys/os_str/bytes.rs +++ b/library/std/src/sys/os_str/bytes.rs @@ -1,6 +1,9 @@ //! The underlying OsString/OsStr implementation on Unix and many other //! systems: just a `Vec<u8>`/`[u8]`. +use core::clone::CloneToUninit; +use core::ptr::addr_of_mut; + use crate::borrow::Cow; use crate::collections::TryReserveError; use crate::fmt::Write; @@ -345,3 +348,13 @@ impl Slice { self.inner.eq_ignore_ascii_case(&other.inner) } } + +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for Slice { + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: we're just a wrapper around [u8] + unsafe { self.inner.clone_to_uninit(addr_of_mut!((*dst).inner)) } + } +} diff --git a/library/std/src/sys/os_str/wtf8.rs b/library/std/src/sys/os_str/wtf8.rs index ed975ba58b5..433237aa6e7 100644 --- a/library/std/src/sys/os_str/wtf8.rs +++ b/library/std/src/sys/os_str/wtf8.rs @@ -1,5 +1,8 @@ //! The underlying OsString/OsStr implementation on Windows is a //! wrapper around the "WTF-8" encoding; see the `wtf8` module for more. +use core::clone::CloneToUninit; +use core::ptr::addr_of_mut; + use crate::borrow::Cow; use crate::collections::TryReserveError; use crate::rc::Rc; @@ -268,3 +271,13 @@ impl Slice { self.inner.eq_ignore_ascii_case(&other.inner) } } + +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for Slice { + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: we're just a wrapper around Wtf8 + unsafe { self.inner.clone_to_uninit(addr_of_mut!((*dst).inner)) } + } +} diff --git a/library/std/src/sys_common/wtf8.rs b/library/std/src/sys_common/wtf8.rs index 277c9506feb..063451ad54e 100644 --- a/library/std/src/sys_common/wtf8.rs +++ b/library/std/src/sys_common/wtf8.rs @@ -19,12 +19,14 @@ mod tests; use core::char::{encode_utf16_raw, encode_utf8_raw}; +use core::clone::CloneToUninit; use core::str::next_code_point; use crate::borrow::Cow; use crate::collections::TryReserveError; use crate::hash::{Hash, Hasher}; use crate::iter::FusedIterator; +use crate::ptr::addr_of_mut; use crate::rc::Rc; use crate::sync::Arc; use crate::sys_common::AsInner; @@ -1046,3 +1048,13 @@ impl Hash for Wtf8 { 0xfeu8.hash(state) } } + +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for Wtf8 { + #[inline] + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: we're just a wrapper around [u8] + unsafe { self.bytes.clone_to_uninit(addr_of_mut!((*dst).bytes)) } + } +} |