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Commit 245a28e

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Support vec![const { ... }; n] syntax
1 parent 124eb96 commit 245a28e

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4 files changed

+78
-0
lines changed

4 files changed

+78
-0
lines changed

‎library/alloc/src/macros.rs

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@@ -43,6 +43,10 @@ macro_rules! vec {
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() => (
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$crate::vec::Vec::new()
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);
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(const $elem:block; $n:expr) => (
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// SAFETY: The `const` keyword asserts the value being the result of a const expression.
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unsafe { $crate::vec::from_const_elem(const $elem, $n) }
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);
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($elem:expr; $n:expr) => (
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$crate::vec::from_elem($elem, $n)
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);

‎library/alloc/src/vec/mod.rs

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@@ -3183,6 +3183,57 @@ pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<
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<T as SpecFromElem>::from_elem(elem, n, alloc)
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}
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/// # Safety
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///
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/// `value` must points to a valid `T` value that is the result of some const expression.
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unsafe fn fill_const_value<T>(buffer: &mut [MaybeUninit<T>], value: *const T) {
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for target in buffer {
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// SAFETY: If `value` is the result of some const expression, we can make as many copies as
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// needed.
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unsafe { target.write(ptr::read(value)) };
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}
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}
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/// # Safety
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///
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/// `elem` must be the result of some const expression.
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#[doc(hidden)]
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#[cfg(not(no_global_oom_handling))]
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#[unstable(feature = "vec_of_const_expr", issue = "none")]
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#[track_caller]
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pub unsafe fn from_const_elem<T>(elem: T, n: usize) -> Vec<T> {
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// SAFETY: Caller has guaranteed `elem` being the result of some const expression.
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unsafe { from_const_elem_in(elem, n, Global) }
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}
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/// # Safety
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///
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/// `elem` must be the result of some const expression.
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#[doc(hidden)]
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#[cfg(not(no_global_oom_handling))]
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#[unstable(feature = "vec_of_const_expr", issue = "none")]
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#[track_caller]
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unsafe fn from_const_elem_in<T, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
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// Avoid calling the destructor of `elem`.
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let elem = ManuallyDrop::new(elem);
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let elem_ptr = ptr::from_ref(&*elem);
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let mut result = Vec::<T, A>::with_capacity_in(n, alloc);
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let buffer_ptr = result.as_mut_ptr().cast::<MaybeUninit<T>>();
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// SAFETY: `with_capacity_in` makes sure the capacity is at least `n`, so we can make a buffer
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// of length `n` out of it.
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let buffer = unsafe { slice::from_raw_parts_mut(buffer_ptr, n) };
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// SAFETY: Caller has guaranteed `elem` being the result of some const expression.
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unsafe { fill_const_value(buffer, elem_ptr) };
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// SAFETY: We have initialized exactly `n` values at the start of the buffer, so we are safe to
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// set the length accordingly.
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unsafe { result.set_len(n) };
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result
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}
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#[cfg(not(no_global_oom_handling))]
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trait ExtendFromWithinSpec {
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/// # Safety

‎library/alloc/tests/lib.rs

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Original file line numberDiff line numberDiff line change
@@ -36,6 +36,7 @@
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#![cfg_attr(not(bootstrap), feature(strict_provenance_lints))]
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#![feature(drain_keep_rest)]
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#![feature(local_waker)]
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#![feature(vec_of_const_expr)]
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#![feature(vec_pop_if)]
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#![feature(unique_rc_arc)]
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#![feature(macro_metavar_expr_concat)]

‎library/alloc/tests/vec.rs

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Original file line numberDiff line numberDiff line change
@@ -2311,6 +2311,28 @@ fn test_vec_macro_repeat() {
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assert_eq!(vec![el; n], vec![Box::new(1), Box::new(1), Box::new(1)]);
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}
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#[test]
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fn test_vec_macro_repeat_const() {
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#[derive(Eq, PartialEq, Debug)]
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struct Item {
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x: u64,
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y: u32, // Paddings are added to test the uninitialized bytes case.
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}
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impl Clone for Item {
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fn clone(&self) -> Self {
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panic!("no clone should be called");
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}
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}
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const ITEM: Item = Item { x: 2, y: 3 };
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assert_eq!(vec![const { ITEM }; 0], vec![ITEM; 0]);
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assert_eq!(vec![const { ITEM }; 1], vec![ITEM]);
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assert_eq!(vec![const { ITEM }; 2], vec![ITEM, ITEM]);
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assert_eq!(vec![const { ITEM }; 3], vec![ITEM, ITEM, ITEM]);
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}
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#[test]
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fn test_vec_swap() {
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let mut a: Vec<isize> = vec![0, 1, 2, 3, 4, 5, 6];

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