bump-scope 2.3.0

A fast bump allocator that supports allocation scopes / checkpoints. Aka an arena for values of arbitrary types.
Documentation 
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use core::{alloc::Layout, ptr::NonNull};

use crate::{
    alloc::{AllocError, Allocator},
    polyfill::non_null,
    traits::BumpAllocatorCore,
};

/// Wraps a bump allocator and does nothing on [`deallocate`](Allocator::deallocate).
///
/// This type only implements [`Allocator`] for wrapped types that implement [`BumpAllocatorCore`], so you don't accidentally leak memory.
///
/// # Examples
///
/// ```
/// # #[cfg(feature = "allocator-api2-04")]
/// # {
/// use bump_scope::{Bump, WithoutDealloc};
/// use allocator_api2_04::boxed::Box;
///
/// let bump: Bump = Bump::new();
///
/// let boxed = Box::new_in(5, &bump);
/// assert_eq!(bump.stats().allocated(), 4);
/// drop(boxed);
/// assert_eq!(bump.stats().allocated(), 0);
///
/// let boxed = Box::new_in(5, WithoutDealloc(&bump));
/// assert_eq!(bump.stats().allocated(), 4);
/// drop(boxed);
/// assert_eq!(bump.stats().allocated(), 4);
/// # }
/// ```
#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct WithoutDealloc<A>(pub A);

unsafe impl<A: BumpAllocatorCore> Allocator for WithoutDealloc<A> {
    #[inline(always)]
    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        self.0.allocate(layout)
    }

    #[inline(always)]
    fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        self.0.allocate_zeroed(layout)
    }

    #[inline(always)]
    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
        let _ = (ptr, layout);
    }

    #[inline(always)]
    unsafe fn grow(&self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        unsafe { self.0.grow(ptr, old_layout, new_layout) }
    }

    #[inline(always)]
    unsafe fn grow_zeroed(
        &self,
        ptr: NonNull<u8>,
        old_layout: Layout,
        new_layout: Layout,
    ) -> Result<NonNull<[u8]>, AllocError> {
        unsafe { self.0.grow_zeroed(ptr, old_layout, new_layout) }
    }

    #[inline(always)]
    unsafe fn shrink(&self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        unsafe { self.0.shrink(ptr, old_layout, new_layout) }
    }
}

/// Wraps a bump allocator and does nothing on [`shrink`](Allocator::shrink).
///
/// This type only implements [`Allocator`] for wrapped types that implement [`BumpAllocatorCore`], so you don't accidentally leak memory.
#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct WithoutShrink<A>(pub A);

unsafe impl<A: BumpAllocatorCore> Allocator for WithoutShrink<A> {
    #[inline(always)]
    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        self.0.allocate(layout)
    }

    #[inline(always)]
    fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        self.0.allocate_zeroed(layout)
    }

    #[inline(always)]
    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
        unsafe { self.0.deallocate(ptr, layout) };
    }

    #[inline(always)]
    unsafe fn grow(&self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        unsafe { self.0.grow(ptr, old_layout, new_layout) }
    }

    #[inline(always)]
    unsafe fn grow_zeroed(
        &self,
        ptr: NonNull<u8>,
        old_layout: Layout,
        new_layout: Layout,
    ) -> Result<NonNull<[u8]>, AllocError> {
        unsafe { self.0.grow_zeroed(ptr, old_layout, new_layout) }
    }

    #[inline(always)]
    unsafe fn shrink(&self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        #[cold]
        #[inline(never)]
        unsafe fn shrink_unfit<A: BumpAllocatorCore>(
            this: &WithoutShrink<A>,
            ptr: NonNull<u8>,
            old_layout: Layout,
            new_layout: Layout,
        ) -> Result<NonNull<[u8]>, AllocError> {
            let new_ptr = this.0.allocate(new_layout)?.cast::<u8>();
            unsafe { ptr.copy_to_nonoverlapping(new_ptr, old_layout.size()) };
            Ok(NonNull::slice_from_raw_parts(new_ptr, new_layout.size()))
        }

        unsafe {
            if non_null::is_aligned_to(ptr, new_layout.align()) {
                Ok(NonNull::slice_from_raw_parts(ptr, new_layout.size()))
            } else {
                // expected to virtually never occur
                shrink_unfit(self, ptr, old_layout, new_layout)
            }
        }
    }
}