From 97b7170eef055e88feb6d5d7eace6c8c35acb7e2 Mon Sep 17 00:00:00 2001 From: ltdk Date: Thu, 16 Oct 2025 15:04:43 -0400 Subject: [PATCH 1/2] const Cell methods --- library/core/src/cell.rs | 21 +++++++++++++++++---- library/coretests/tests/lib.rs | 1 + library/coretests/tests/ptr.rs | 29 ++++++++++++++--------------- 3 files changed, 32 insertions(+), 19 deletions(-) diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs index aeac35e45a5d0..988c50795e299 100644 --- a/library/core/src/cell.rs +++ b/library/core/src/cell.rs @@ -252,7 +252,7 @@ use crate::cmp::Ordering; use crate::fmt::{self, Debug, Display}; -use crate::marker::{PhantomData, Unsize}; +use crate::marker::{Destruct, PhantomData, Unsize}; use crate::mem::{self, ManuallyDrop}; use crate::ops::{self, CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn}; use crate::panic::const_panic; @@ -429,7 +429,11 @@ impl Cell { /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] - pub fn set(&self, val: T) { + #[rustc_const_unstable(feature = "const_cell_traits", issue = "147787")] + pub const fn set(&self, val: T) + where + T: [const] Destruct, + { self.replace(val); } @@ -561,7 +565,12 @@ impl Cell { /// ``` #[inline] #[stable(feature = "cell_update", since = "1.88.0")] - pub fn update(&self, f: impl FnOnce(T) -> T) { + #[rustc_const_unstable(feature = "const_cell_traits", issue = "147787")] + pub const fn update(&self, f: impl [const] FnOnce(T) -> T) + where + // FIXME(const-hack): `Copy` should imply `const Destruct` + T: [const] Destruct, + { let old = self.get(); self.set(f(old)); } @@ -654,7 +663,11 @@ impl Cell { /// assert_eq!(c.into_inner(), 0); /// ``` #[stable(feature = "move_cell", since = "1.17.0")] - pub fn take(&self) -> T { + #[rustc_const_unstable(feature = "const_cell_traits", issue = "147787")] + pub const fn take(&self) -> T + where + T: [const] Default, + { self.replace(Default::default()) } } diff --git a/library/coretests/tests/lib.rs b/library/coretests/tests/lib.rs index c2dc3a99ab109..5c2522acb1362 100644 --- a/library/coretests/tests/lib.rs +++ b/library/coretests/tests/lib.rs @@ -16,6 +16,7 @@ #![feature(char_internals)] #![feature(char_max_len)] #![feature(clone_to_uninit)] +#![feature(const_cell_traits)] #![feature(const_cmp)] #![feature(const_convert)] #![feature(const_destruct)] diff --git a/library/coretests/tests/ptr.rs b/library/coretests/tests/ptr.rs index e89f21271027a..7afbb1260f239 100644 --- a/library/coretests/tests/ptr.rs +++ b/library/coretests/tests/ptr.rs @@ -1049,38 +1049,37 @@ fn test_ptr_default() { #[test] fn test_const_drop_in_place() { const COUNTER: usize = { - let mut counter = 0; - let counter_ptr = &raw mut counter; + use core::cell::Cell; + + let counter = Cell::new(0); // only exists to make `Drop` indirect impl #[allow(dead_code)] - struct Test(Dropped); + struct Test<'a>(Dropped<'a>); - struct Dropped(*mut usize); - impl const Drop for Dropped { + struct Dropped<'a>(&'a Cell); + impl const Drop for Dropped<'_> { fn drop(&mut self) { - unsafe { - *self.0 += 1; - } + self.0.set(self.0.get() + 1); } } - let mut one = ManuallyDrop::new(Test(Dropped(counter_ptr))); - let mut two = ManuallyDrop::new(Test(Dropped(counter_ptr))); - let mut three = ManuallyDrop::new(Test(Dropped(counter_ptr))); - assert!(counter == 0); + let mut one = ManuallyDrop::new(Test(Dropped(&counter))); + let mut two = ManuallyDrop::new(Test(Dropped(&counter))); + let mut three = ManuallyDrop::new(Test(Dropped(&counter))); + assert!(counter.get() == 0); unsafe { ManuallyDrop::drop(&mut one); } - assert!(counter == 1); + assert!(counter.get() == 1); unsafe { ManuallyDrop::drop(&mut two); } - assert!(counter == 2); + assert!(counter.get() == 2); unsafe { ManuallyDrop::drop(&mut three); } - counter + counter.get() }; assert_eq!(COUNTER, 3); } From 31a2c565bd6f0f4a58fd445c88465e7268bfdb80 Mon Sep 17 00:00:00 2001 From: ltdk Date: Sun, 19 Oct 2025 02:44:41 -0400 Subject: [PATCH 2/2] Move const_drop_in_place test from ptr to manually_drop module --- library/coretests/tests/manually_drop.rs | 38 ++++++++++++++++++++++ library/coretests/tests/ptr.rs | 40 +----------------------- 2 files changed, 39 insertions(+), 39 deletions(-) diff --git a/library/coretests/tests/manually_drop.rs b/library/coretests/tests/manually_drop.rs index bbf444471ad2a..1638c82b161b4 100644 --- a/library/coretests/tests/manually_drop.rs +++ b/library/coretests/tests/manually_drop.rs @@ -27,3 +27,41 @@ fn smoke() { drop(x); drop(y); } + +#[test] +fn const_drop_in_place() { + const COUNTER: usize = { + use core::cell::Cell; + + let counter = Cell::new(0); + + // only exists to make `Drop` indirect impl + #[allow(dead_code)] + struct Test<'a>(Dropped<'a>); + + struct Dropped<'a>(&'a Cell); + impl const Drop for Dropped<'_> { + fn drop(&mut self) { + self.0.set(self.0.get() + 1); + } + } + + let mut one = ManuallyDrop::new(Test(Dropped(&counter))); + let mut two = ManuallyDrop::new(Test(Dropped(&counter))); + let mut three = ManuallyDrop::new(Test(Dropped(&counter))); + assert!(counter.get() == 0); + unsafe { + ManuallyDrop::drop(&mut one); + } + assert!(counter.get() == 1); + unsafe { + ManuallyDrop::drop(&mut two); + } + assert!(counter.get() == 2); + unsafe { + ManuallyDrop::drop(&mut three); + } + counter.get() + }; + assert_eq!(COUNTER, 3); +} diff --git a/library/coretests/tests/ptr.rs b/library/coretests/tests/ptr.rs index 7afbb1260f239..4d5138d539b95 100644 --- a/library/coretests/tests/ptr.rs +++ b/library/coretests/tests/ptr.rs @@ -1,6 +1,6 @@ use core::cell::RefCell; use core::marker::Freeze; -use core::mem::{ManuallyDrop, MaybeUninit}; +use core::mem::MaybeUninit; use core::num::NonZero; use core::ptr; use core::ptr::*; @@ -1045,41 +1045,3 @@ fn test_ptr_default() { let default = PtrMutDefaultTest::default(); assert!(default.ptr.is_null()); } - -#[test] -fn test_const_drop_in_place() { - const COUNTER: usize = { - use core::cell::Cell; - - let counter = Cell::new(0); - - // only exists to make `Drop` indirect impl - #[allow(dead_code)] - struct Test<'a>(Dropped<'a>); - - struct Dropped<'a>(&'a Cell); - impl const Drop for Dropped<'_> { - fn drop(&mut self) { - self.0.set(self.0.get() + 1); - } - } - - let mut one = ManuallyDrop::new(Test(Dropped(&counter))); - let mut two = ManuallyDrop::new(Test(Dropped(&counter))); - let mut three = ManuallyDrop::new(Test(Dropped(&counter))); - assert!(counter.get() == 0); - unsafe { - ManuallyDrop::drop(&mut one); - } - assert!(counter.get() == 1); - unsafe { - ManuallyDrop::drop(&mut two); - } - assert!(counter.get() == 2); - unsafe { - ManuallyDrop::drop(&mut three); - } - counter.get() - }; - assert_eq!(COUNTER, 3); -}