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| 1 | +//! Rust standard library vendored code. |
| 2 | +//! |
| 3 | +//! The contents of this file come from the Rust standard library, hosted in |
| 4 | +//! the <https://github.com/rust-lang/rust> repository, licensed under |
| 5 | +//! "Apache-2.0 OR MIT" and adapted for kernel use. For copyright details, |
| 6 | +//! see <https://github.com/rust-lang/rust/blob/master/COPYRIGHT>. |
| 7 | +#![allow(clippy::undocumented_unsafe_blocks)] |
| 8 | + |
| 9 | +use core::fmt; |
| 10 | +use core::iter::FusedIterator; |
| 11 | +use core::mem::{self, ManuallyDrop, SizedTypeProperties}; |
| 12 | +use core::ptr::{self, NonNull}; |
| 13 | +use core::slice::{self}; |
| 14 | + |
| 15 | +use super::{kvec::Vec, Allocator}; |
| 16 | + |
| 17 | +/// A draining iterator for `Vec<T>`. |
| 18 | +/// |
| 19 | +/// This `struct` is created by [`Vec::drain`]. |
| 20 | +/// See its documentation for more. |
| 21 | +/// |
| 22 | +/// # Example |
| 23 | +/// |
| 24 | +/// ``` |
| 25 | +/// let mut v = vec![0, 1, 2]; |
| 26 | +/// let iter: std::vec::Drain<'_, _> = v.drain(..); |
| 27 | +/// ``` |
| 28 | +// #[stable(feature = "drain", since = "1.6.0")] |
| 29 | +pub struct Drain< |
| 30 | + 'a, |
| 31 | + T: 'a, |
| 32 | + A: Allocator, |
| 33 | + // #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global, |
| 34 | +> { |
| 35 | + /// Index of tail to preserve |
| 36 | + pub(super) tail_start: usize, |
| 37 | + /// Length of tail |
| 38 | + pub(super) tail_len: usize, |
| 39 | + /// Current remaining range to remove |
| 40 | + pub(super) iter: slice::Iter<'a, T>, |
| 41 | + pub(super) vec: NonNull<Vec<T, A>>, |
| 42 | +} |
| 43 | + |
| 44 | +// #[stable(feature = "collection_debug", since = "1.17.0")] |
| 45 | +impl<T: fmt::Debug, A: Allocator> fmt::Debug for Drain<'_, T, A> { |
| 46 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 47 | + f.debug_tuple("Drain").field(&self.iter.as_slice()).finish() |
| 48 | + } |
| 49 | +} |
| 50 | + |
| 51 | +impl<'a, T, A: Allocator> Drain<'a, T, A> { |
| 52 | + /// Returns the remaining items of this iterator as a slice. |
| 53 | + /// |
| 54 | + /// # Examples |
| 55 | + /// |
| 56 | + /// ``` |
| 57 | + /// let mut vec = vec!['a', 'b', 'c']; |
| 58 | + /// let mut drain = vec.drain(..); |
| 59 | + /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']); |
| 60 | + /// let _ = drain.next().unwrap(); |
| 61 | + /// assert_eq!(drain.as_slice(), &['b', 'c']); |
| 62 | + /// ``` |
| 63 | + #[must_use] |
| 64 | + // #[stable(feature = "vec_drain_as_slice", since = "1.46.0")] |
| 65 | + pub fn as_slice(&self) -> &[T] { |
| 66 | + self.iter.as_slice() |
| 67 | + } |
| 68 | + |
| 69 | + /// Keep unyielded elements in the source `Vec`. |
| 70 | + /// |
| 71 | + /// # Examples |
| 72 | + /// |
| 73 | + /// ``` |
| 74 | + /// #![feature(drain_keep_rest)] |
| 75 | + /// |
| 76 | + /// let mut vec = vec!['a', 'b', 'c']; |
| 77 | + /// let mut drain = vec.drain(..); |
| 78 | + /// |
| 79 | + /// assert_eq!(drain.next().unwrap(), 'a'); |
| 80 | + /// |
| 81 | + /// // This call keeps 'b' and 'c' in the vec. |
| 82 | + /// drain.keep_rest(); |
| 83 | + /// |
| 84 | + /// // If we wouldn't call `keep_rest()`, |
| 85 | + /// // `vec` would be empty. |
| 86 | + /// assert_eq!(vec, ['b', 'c']); |
| 87 | + /// ``` |
| 88 | + // #[unstable(feature = "drain_keep_rest", issue = "101122")] |
| 89 | + pub fn keep_rest(self) { |
| 90 | + // At this moment layout looks like this: |
| 91 | + // |
| 92 | + // [head] [yielded by next] [unyielded] [yielded by next_back] [tail] |
| 93 | + // ^-- start \_________/-- unyielded_len \____/-- self.tail_len |
| 94 | + // ^-- unyielded_ptr ^-- tail |
| 95 | + // |
| 96 | + // Normally `Drop` impl would drop [unyielded] and then move [tail] to the `start`. |
| 97 | + // Here we want to |
| 98 | + // 1. Move [unyielded] to `start` |
| 99 | + // 2. Move [tail] to a new start at `start + len(unyielded)` |
| 100 | + // 3. Update length of the original vec to `len(head) + len(unyielded) + len(tail)` |
| 101 | + // a. In case of ZST, this is the only thing we want to do |
| 102 | + // 4. Do *not* drop self, as everything is put in a consistent state already, there is nothing to do |
| 103 | + let mut this = ManuallyDrop::new(self); |
| 104 | + |
| 105 | + unsafe { |
| 106 | + let source_vec = this.vec.as_mut(); |
| 107 | + |
| 108 | + let start = source_vec.len(); |
| 109 | + let tail = this.tail_start; |
| 110 | + |
| 111 | + let unyielded_len = this.iter.len(); |
| 112 | + let unyielded_ptr = this.iter.as_slice().as_ptr(); |
| 113 | + |
| 114 | + // ZSTs have no identity, so we don't need to move them around. |
| 115 | + if !T::IS_ZST { |
| 116 | + let start_ptr = source_vec.as_mut_ptr().add(start); |
| 117 | + |
| 118 | + // memmove back unyielded elements |
| 119 | + if unyielded_ptr != start_ptr { |
| 120 | + let src = unyielded_ptr; |
| 121 | + let dst = start_ptr; |
| 122 | + |
| 123 | + ptr::copy(src, dst, unyielded_len); |
| 124 | + } |
| 125 | + |
| 126 | + // memmove back untouched tail |
| 127 | + if tail != (start + unyielded_len) { |
| 128 | + let src = source_vec.as_ptr().add(tail); |
| 129 | + let dst = start_ptr.add(unyielded_len); |
| 130 | + ptr::copy(src, dst, this.tail_len); |
| 131 | + } |
| 132 | + } |
| 133 | + |
| 134 | + source_vec.set_len(start + unyielded_len + this.tail_len); |
| 135 | + } |
| 136 | + } |
| 137 | +} |
| 138 | + |
| 139 | +// #[stable(feature = "vec_drain_as_slice", since = "1.46.0")] |
| 140 | +impl<'a, T, A: Allocator> AsRef<[T]> for Drain<'a, T, A> { |
| 141 | + fn as_ref(&self) -> &[T] { |
| 142 | + self.as_slice() |
| 143 | + } |
| 144 | +} |
| 145 | + |
| 146 | +// #[stable(feature = "drain", since = "1.6.0")] |
| 147 | +unsafe impl<T: Sync, A: Sync + Allocator> Sync for Drain<'_, T, A> {} |
| 148 | +// #[stable(feature = "drain", since = "1.6.0")] |
| 149 | +unsafe impl<T: Send, A: Send + Allocator> Send for Drain<'_, T, A> {} |
| 150 | + |
| 151 | +// #[stable(feature = "drain", since = "1.6.0")] |
| 152 | +impl<T, A: Allocator> Iterator for Drain<'_, T, A> { |
| 153 | + type Item = T; |
| 154 | + |
| 155 | + #[inline] |
| 156 | + fn next(&mut self) -> Option<T> { |
| 157 | + self.iter |
| 158 | + .next() |
| 159 | + .map(|elt| unsafe { ptr::read(elt as *const _) }) |
| 160 | + } |
| 161 | + |
| 162 | + fn size_hint(&self) -> (usize, Option<usize>) { |
| 163 | + self.iter.size_hint() |
| 164 | + } |
| 165 | +} |
| 166 | + |
| 167 | +// #[stable(feature = "drain", since = "1.6.0")] |
| 168 | +impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> { |
| 169 | + #[inline] |
| 170 | + fn next_back(&mut self) -> Option<T> { |
| 171 | + self.iter |
| 172 | + .next_back() |
| 173 | + .map(|elt| unsafe { ptr::read(elt as *const _) }) |
| 174 | + } |
| 175 | +} |
| 176 | + |
| 177 | +// #[stable(feature = "drain", since = "1.6.0")] |
| 178 | +impl<T, A: Allocator> Drop for Drain<'_, T, A> { |
| 179 | + fn drop(&mut self) { |
| 180 | + /// Moves back the un-`Drain`ed elements to restore the original `Vec`. |
| 181 | + struct DropGuard<'r, 'a, T, A: Allocator>(&'r mut Drain<'a, T, A>); |
| 182 | + |
| 183 | + impl<'r, 'a, T, A: Allocator> Drop for DropGuard<'r, 'a, T, A> { |
| 184 | + fn drop(&mut self) { |
| 185 | + if self.0.tail_len > 0 { |
| 186 | + unsafe { |
| 187 | + let source_vec = self.0.vec.as_mut(); |
| 188 | + // memmove back untouched tail, update to new length |
| 189 | + let start = source_vec.len(); |
| 190 | + let tail = self.0.tail_start; |
| 191 | + if tail != start { |
| 192 | + let src = source_vec.as_ptr().add(tail); |
| 193 | + let dst = source_vec.as_mut_ptr().add(start); |
| 194 | + ptr::copy(src, dst, self.0.tail_len); |
| 195 | + } |
| 196 | + source_vec.set_len(start + self.0.tail_len); |
| 197 | + } |
| 198 | + } |
| 199 | + } |
| 200 | + } |
| 201 | + |
| 202 | + let iter = mem::take(&mut self.iter); |
| 203 | + let drop_len = iter.len(); |
| 204 | + |
| 205 | + let mut vec = self.vec; |
| 206 | + |
| 207 | + if T::IS_ZST { |
| 208 | + // ZSTs have no identity, so we don't need to move them around, we only need to drop the correct amount. |
| 209 | + // this can be achieved by manipulating the Vec length instead of moving values out from `iter`. |
| 210 | + unsafe { |
| 211 | + let vec = vec.as_mut(); |
| 212 | + let old_len = vec.len(); |
| 213 | + vec.set_len(old_len + drop_len + self.tail_len); |
| 214 | + vec.truncate(old_len + self.tail_len); |
| 215 | + } |
| 216 | + |
| 217 | + return; |
| 218 | + } |
| 219 | + |
| 220 | + // ensure elements are moved back into their appropriate places, even when drop_in_place panics |
| 221 | + let _guard = DropGuard(self); |
| 222 | + |
| 223 | + if drop_len == 0 { |
| 224 | + return; |
| 225 | + } |
| 226 | + |
| 227 | + // as_slice() must only be called when iter.len() is > 0 because |
| 228 | + // it also gets touched by vec::Splice which may turn it into a dangling pointer |
| 229 | + // which would make it and the vec pointer point to different allocations which would |
| 230 | + // lead to invalid pointer arithmetic below. |
| 231 | + let drop_ptr = iter.as_slice().as_ptr(); |
| 232 | + |
| 233 | + unsafe { |
| 234 | + // drop_ptr comes from a slice::Iter which only gives us a &[T] but for drop_in_place |
| 235 | + // a pointer with mutable provenance is necessary. Therefore we must reconstruct |
| 236 | + // it from the original vec but also avoid creating a &mut to the front since that could |
| 237 | + // invalidate raw pointers to it which some unsafe code might rely on. |
| 238 | + let vec_ptr = vec.as_mut().as_mut_ptr(); |
| 239 | + let drop_offset = drop_ptr.sub_ptr(vec_ptr); |
| 240 | + let to_drop = ptr::slice_from_raw_parts_mut(vec_ptr.add(drop_offset), drop_len); |
| 241 | + ptr::drop_in_place(to_drop); |
| 242 | + } |
| 243 | + } |
| 244 | +} |
| 245 | + |
| 246 | +// #[stable(feature = "fused", since = "1.26.0")] |
| 247 | +impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {} |
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