Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 794 insertions, 0 deletions

diff --git a/third_party/rust/bumpalo/src/alloc.rs b/third_party/rust/bumpalo/src/alloc.rs
new file mode 100644
index 0000000000..0bcc21f22c
--- /dev/null
+++ b/third_party/rust/bumpalo/src/alloc.rs
@@ -0,0 +1,794 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(unstable_name_collisions)]
+#![allow(dead_code)]
+#![allow(deprecated)]
+
+//! Memory allocation APIs
+
+use core::cmp;
+use core::fmt;
+use core::mem;
+use core::ptr::{self, NonNull};
+use core::usize;
+
+pub use core::alloc::{Layout, LayoutErr};
+
+fn new_layout_err() -> LayoutErr {
+    Layout::from_size_align(1, 3).unwrap_err()
+}
+
+pub fn handle_alloc_error(layout: Layout) -> ! {
+    panic!("encountered allocation error: {:?}", layout)
+}
+
+pub trait UnstableLayoutMethods {
+    fn padding_needed_for(&self, align: usize) -> usize;
+    fn repeat(&self, n: usize) -> Result<(Layout, usize), LayoutErr>;
+    fn array<T>(n: usize) -> Result<Layout, LayoutErr>;
+}
+
+impl UnstableLayoutMethods for Layout {
+    fn padding_needed_for(&self, align: usize) -> usize {
+        let len = self.size();
+
+        // Rounded up value is:
+        //   len_rounded_up = (len + align - 1) & !(align - 1);
+        // and then we return the padding difference: `len_rounded_up - len`.
+        //
+        // We use modular arithmetic throughout:
+        //
+        // 1. align is guaranteed to be > 0, so align - 1 is always
+        //    valid.
+        //
+        // 2. `len + align - 1` can overflow by at most `align - 1`,
+        //    so the &-mask with `!(align - 1)` will ensure that in the
+        //    case of overflow, `len_rounded_up` will itself be 0.
+        //    Thus the returned padding, when added to `len`, yields 0,
+        //    which trivially satisfies the alignment `align`.
+        //
+        // (Of course, attempts to allocate blocks of memory whose
+        // size and padding overflow in the above manner should cause
+        // the allocator to yield an error anyway.)
+
+        let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
+        len_rounded_up.wrapping_sub(len)
+    }
+
+    fn repeat(&self, n: usize) -> Result<(Layout, usize), LayoutErr> {
+        let padded_size = self
+            .size()
+            .checked_add(self.padding_needed_for(self.align()))
+            .ok_or_else(new_layout_err)?;
+        let alloc_size = padded_size.checked_mul(n).ok_or_else(new_layout_err)?;
+
+        unsafe {
+            // self.align is already known to be valid and alloc_size has been
+            // padded already.
+            Ok((
+                Layout::from_size_align_unchecked(alloc_size, self.align()),
+                padded_size,
+            ))
+        }
+    }
+
+    fn array<T>(n: usize) -> Result<Layout, LayoutErr> {
+        Layout::new::<T>().repeat(n).map(|(k, offs)| {
+            debug_assert!(offs == mem::size_of::<T>());
+            k
+        })
+    }
+}
+
+/// Represents the combination of a starting address and
+/// a total capacity of the returned block.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Debug)]
+pub struct Excess(pub NonNull<u8>, pub usize);
+
+fn size_align<T>() -> (usize, usize) {
+    (mem::size_of::<T>(), mem::align_of::<T>())
+}
+
+/// The `AllocErr` error indicates an allocation failure
+/// that may be due to resource exhaustion or to
+/// something wrong when combining the given input arguments with this
+/// allocator.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct AllocErr;
+
+// (we need this for downstream impl of trait Error)
+// #[unstable(feature = "allocator_api", issue = "32838")]
+impl fmt::Display for AllocErr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("memory allocation failed")
+    }
+}
+
+/// The `CannotReallocInPlace` error is used when `grow_in_place` or
+/// `shrink_in_place` were unable to reuse the given memory block for
+/// a requested layout.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct CannotReallocInPlace;
+
+// #[unstable(feature = "allocator_api", issue = "32838")]
+impl CannotReallocInPlace {
+    pub fn description(&self) -> &str {
+        "cannot reallocate allocator's memory in place"
+    }
+}
+
+// (we need this for downstream impl of trait Error)
+// #[unstable(feature = "allocator_api", issue = "32838")]
+impl fmt::Display for CannotReallocInPlace {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.description())
+    }
+}
+
+/// An implementation of `Alloc` can allocate, reallocate, and
+/// deallocate arbitrary blocks of data described via `Layout`.
+///
+/// Some of the methods require that a memory block be *currently
+/// allocated* via an allocator. This means that:
+///
+/// * the starting address for that memory block was previously
+///   returned by a previous call to an allocation method (`alloc`,
+///   `alloc_zeroed`, `alloc_excess`, `alloc_one`, `alloc_array`) or
+///   reallocation method (`realloc`, `realloc_excess`, or
+///   `realloc_array`), and
+///
+/// * the memory block has not been subsequently deallocated, where
+///   blocks are deallocated either by being passed to a deallocation
+///   method (`dealloc`, `dealloc_one`, `dealloc_array`) or by being
+///   passed to a reallocation method (see above) that returns `Ok`.
+///
+/// A note regarding zero-sized types and zero-sized layouts: many
+/// methods in the `Alloc` trait state that allocation requests
+/// must be non-zero size, or else undefined behavior can result.
+///
+/// * However, some higher-level allocation methods (`alloc_one`,
+///   `alloc_array`) are well-defined on zero-sized types and can
+///   optionally support them: it is left up to the implementor
+///   whether to return `Err`, or to return `Ok` with some pointer.
+///
+/// * If an `Alloc` implementation chooses to return `Ok` in this
+///   case (i.e. the pointer denotes a zero-sized inaccessible block)
+///   then that returned pointer must be considered "currently
+///   allocated". On such an allocator, *all* methods that take
+///   currently-allocated pointers as inputs must accept these
+///   zero-sized pointers, *without* causing undefined behavior.
+///
+/// * In other words, if a zero-sized pointer can flow out of an
+///   allocator, then that allocator must likewise accept that pointer
+///   flowing back into its deallocation and reallocation methods.
+///
+/// Some of the methods require that a layout *fit* a memory block.
+/// What it means for a layout to "fit" a memory block means (or
+/// equivalently, for a memory block to "fit" a layout) is that the
+/// following two conditions must hold:
+///
+/// 1. The block's starting address must be aligned to `layout.align()`.
+///
+/// 2. The block's size must fall in the range `[use_min, use_max]`, where:
+///
+///    * `use_min` is `self.usable_size(layout).0`, and
+///
+///    * `use_max` is the capacity that was (or would have been)
+///      returned when (if) the block was allocated via a call to
+///      `alloc_excess` or `realloc_excess`.
+///
+/// Note that:
+///
+///  * the size of the layout most recently used to allocate the block
+///    is guaranteed to be in the range `[use_min, use_max]`, and
+///
+///  * a lower-bound on `use_max` can be safely approximated by a call to
+///    `usable_size`.
+///
+///  * if a layout `k` fits a memory block (denoted by `ptr`)
+///    currently allocated via an allocator `a`, then it is legal to
+///    use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.
+///
+/// # Unsafety
+///
+/// The `Alloc` trait is an `unsafe` trait for a number of reasons, and
+/// implementors must ensure that they adhere to these contracts:
+///
+/// * Pointers returned from allocation functions must point to valid memory and
+///   retain their validity until at least the instance of `Alloc` is dropped
+///   itself.
+///
+/// * `Layout` queries and calculations in general must be correct. Callers of
+///   this trait are allowed to rely on the contracts defined on each method,
+///   and implementors must ensure such contracts remain true.
+///
+/// Note that this list may get tweaked over time as clarifications are made in
+/// the future.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+pub unsafe trait Alloc {
+    // (Note: some existing allocators have unspecified but well-defined
+    // behavior in response to a zero size allocation request ;
+    // e.g. in C, `malloc` of 0 will either return a null pointer or a
+    // unique pointer, but will not have arbitrary undefined
+    // behavior.
+    // However in jemalloc for example,
+    // `mallocx(0)` is documented as undefined behavior.)
+
+    /// Returns a pointer meeting the size and alignment guarantees of
+    /// `layout`.
+    ///
+    /// If this method returns an `Ok(addr)`, then the `addr` returned
+    /// will be non-null address pointing to a block of storage
+    /// suitable for holding an instance of `layout`.
+    ///
+    /// The returned block of storage may or may not have its contents
+    /// initialized. (Extension subtraits might restrict this
+    /// behavior, e.g. to ensure initialization to particular sets of
+    /// bit patterns.)
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure that `layout` has non-zero size.
+    ///
+    /// (Extension subtraits might provide more specific bounds on
+    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// in response to a zero-size allocation request.)
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// Implementations are encouraged to return `Err` on memory
+    /// exhaustion rather than panicking or aborting, but this is not
+    /// a strict requirement. (Specifically: it is *legal* to
+    /// implement this trait atop an underlying native allocation
+    /// library that aborts on memory exhaustion.)
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr>;
+
+    /// Deallocate the memory referenced by `ptr`.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must denote a block of memory currently allocated via
+    ///   this allocator,
+    ///
+    /// * `layout` must *fit* that block of memory,
+    ///
+    /// * In addition to fitting the block of memory `layout`, the
+    ///   alignment of the `layout` must match the alignment used
+    ///   to allocate that block of memory.
+    unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout);
+
+    // == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==
+    // usable_size
+
+    /// Returns bounds on the guaranteed usable size of a successful
+    /// allocation created with the specified `layout`.
+    ///
+    /// In particular, if one has a memory block allocated via a given
+    /// allocator `a` and layout `k` where `a.usable_size(k)` returns
+    /// `(l, u)`, then one can pass that block to `a.dealloc()` with a
+    /// layout in the size range [l, u].
+    ///
+    /// (All implementors of `usable_size` must ensure that
+    /// `l <= k.size() <= u`)
+    ///
+    /// Both the lower- and upper-bounds (`l` and `u` respectively)
+    /// are provided, because an allocator based on size classes could
+    /// misbehave if one attempts to deallocate a block without
+    /// providing a correct value for its size (i.e., one within the
+    /// range `[l, u]`).
+    ///
+    /// Clients who wish to make use of excess capacity are encouraged
+    /// to use the `alloc_excess` and `realloc_excess` instead, as
+    /// this method is constrained to report conservative values that
+    /// serve as valid bounds for *all possible* allocation method
+    /// calls.
+    ///
+    /// However, for clients that do not wish to track the capacity
+    /// returned by `alloc_excess` locally, this method is likely to
+    /// produce useful results.
+    #[inline]
+    fn usable_size(&self, layout: &Layout) -> (usize, usize) {
+        (layout.size(), layout.size())
+    }
+
+    // == METHODS FOR MEMORY REUSE ==
+    // realloc. alloc_excess, realloc_excess
+
+    /// Returns a pointer suitable for holding data described by
+    /// a new layout with `layout`’s alignment and a size given
+    /// by `new_size`. To
+    /// accomplish this, this may extend or shrink the allocation
+    /// referenced by `ptr` to fit the new layout.
+    ///
+    /// If this returns `Ok`, then ownership of the memory block
+    /// referenced by `ptr` has been transferred to this
+    /// allocator. The memory may or may not have been freed, and
+    /// should be considered unusable (unless of course it was
+    /// transferred back to the caller again via the return value of
+    /// this method).
+    ///
+    /// If this method returns `Err`, then ownership of the memory
+    /// block has not been transferred to this allocator, and the
+    /// contents of the memory block are unaltered.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * `layout` must *fit* the `ptr` (see above). (The `new_size`
+    ///   argument need not fit it.)
+    ///
+    /// * `new_size` must be greater than zero.
+    ///
+    /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
+    ///   must not overflow (i.e. the rounded value must be less than `usize::MAX`).
+    ///
+    /// (Extension subtraits might provide more specific bounds on
+    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// in response to a zero-size allocation request.)
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err` only if the new layout
+    /// does not meet the allocator's size
+    /// and alignment constraints of the allocator, or if reallocation
+    /// otherwise fails.
+    ///
+    /// Implementations are encouraged to return `Err` on memory
+    /// exhaustion rather than panicking or aborting, but this is not
+    /// a strict requirement. (Specifically: it is *legal* to
+    /// implement this trait atop an underlying native allocation
+    /// library that aborts on memory exhaustion.)
+    ///
+    /// Clients wishing to abort computation in response to a
+    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn realloc(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<NonNull<u8>, AllocErr> {
+        let old_size = layout.size();
+
+        if new_size >= old_size {
+            if let Ok(()) = self.grow_in_place(ptr, layout, new_size) {
+                return Ok(ptr);
+            }
+        } else if new_size < old_size {
+            if let Ok(()) = self.shrink_in_place(ptr, layout, new_size) {
+                return Ok(ptr);
+            }
+        }
+
+        // otherwise, fall back on alloc + copy + dealloc.
+        let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
+        let result = self.alloc(new_layout);
+        if let Ok(new_ptr) = result {
+            ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), cmp::min(old_size, new_size));
+            self.dealloc(ptr, layout);
+        }
+        result
+    }
+
+    /// Behaves like `alloc`, but also ensures that the contents
+    /// are set to zero before being returned.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `alloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `alloc`.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
+        let size = layout.size();
+        let p = self.alloc(layout);
+        if let Ok(p) = p {
+            ptr::write_bytes(p.as_ptr(), 0, size);
+        }
+        p
+    }
+
+    /// Behaves like `alloc`, but also returns the whole size of
+    /// the returned block. For some `layout` inputs, like arrays, this
+    /// may include extra storage usable for additional data.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `alloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `alloc`.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
+        let usable_size = self.usable_size(&layout);
+        self.alloc(layout).map(|p| Excess(p, usable_size.1))
+    }
+
+    /// Behaves like `realloc`, but also returns the whole size of
+    /// the returned block. For some `layout` inputs, like arrays, this
+    /// may include extra storage usable for additional data.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `realloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `realloc`.
+    ///
+    /// Clients wishing to abort computation in response to a
+    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn realloc_excess(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<Excess, AllocErr> {
+        let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
+        let usable_size = self.usable_size(&new_layout);
+        self.realloc(ptr, layout, new_size)
+            .map(|p| Excess(p, usable_size.1))
+    }
+
+    /// Attempts to extend the allocation referenced by `ptr` to fit `new_size`.
+    ///
+    /// If this returns `Ok`, then the allocator has asserted that the
+    /// memory block referenced by `ptr` now fits `new_size`, and thus can
+    /// be used to carry data of a layout of that size and same alignment as
+    /// `layout`. (The allocator is allowed to
+    /// expend effort to accomplish this, such as extending the memory block to
+    /// include successor blocks, or virtual memory tricks.)
+    ///
+    /// Regardless of what this method returns, ownership of the
+    /// memory block referenced by `ptr` has not been transferred, and
+    /// the contents of the memory block are unaltered.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * `layout` must *fit* the `ptr` (see above); note the
+    ///   `new_size` argument need not fit it,
+    ///
+    /// * `new_size` must not be less than `layout.size()`,
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(CannotReallocInPlace)` when the allocator is
+    /// unable to assert that the memory block referenced by `ptr`
+    /// could fit `layout`.
+    ///
+    /// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`
+    /// function; clients are expected either to be able to recover from
+    /// `grow_in_place` failures without aborting, or to fall back on
+    /// another reallocation method before resorting to an abort.
+    unsafe fn grow_in_place(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<(), CannotReallocInPlace> {
+        let _ = ptr; // this default implementation doesn't care about the actual address.
+        debug_assert!(new_size >= layout.size());
+        let (_l, u) = self.usable_size(&layout);
+        // _l <= layout.size()                       [guaranteed by usable_size()]
+        //       layout.size() <= new_layout.size()  [required by this method]
+        if new_size <= u {
+            Ok(())
+        } else {
+            Err(CannotReallocInPlace)
+        }
+    }
+
+    /// Attempts to shrink the allocation referenced by `ptr` to fit `new_size`.
+    ///
+    /// If this returns `Ok`, then the allocator has asserted that the
+    /// memory block referenced by `ptr` now fits `new_size`, and
+    /// thus can only be used to carry data of that smaller
+    /// layout. (The allocator is allowed to take advantage of this,
+    /// carving off portions of the block for reuse elsewhere.) The
+    /// truncated contents of the block within the smaller layout are
+    /// unaltered, and ownership of block has not been transferred.
+    ///
+    /// If this returns `Err`, then the memory block is considered to
+    /// still represent the original (larger) `layout`. None of the
+    /// block has been carved off for reuse elsewhere, ownership of
+    /// the memory block has not been transferred, and the contents of
+    /// the memory block are unaltered.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * `layout` must *fit* the `ptr` (see above); note the
+    ///   `new_size` argument need not fit it,
+    ///
+    /// * `new_size` must not be greater than `layout.size()`
+    ///   (and must be greater than zero),
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(CannotReallocInPlace)` when the allocator is
+    /// unable to assert that the memory block referenced by `ptr`
+    /// could fit `layout`.
+    ///
+    /// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`
+    /// function; clients are expected either to be able to recover from
+    /// `shrink_in_place` failures without aborting, or to fall back
+    /// on another reallocation method before resorting to an abort.
+    unsafe fn shrink_in_place(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<(), CannotReallocInPlace> {
+        let _ = ptr; // this default implementation doesn't care about the actual address.
+        debug_assert!(new_size <= layout.size());
+        let (l, _u) = self.usable_size(&layout);
+        //                      layout.size() <= _u  [guaranteed by usable_size()]
+        // new_layout.size() <= layout.size()        [required by this method]
+        if l <= new_size {
+            Ok(())
+        } else {
+            Err(CannotReallocInPlace)
+        }
+    }
+
+    // == COMMON USAGE PATTERNS ==
+    // alloc_one, dealloc_one, alloc_array, realloc_array. dealloc_array
+
+    /// Allocates a block suitable for holding an instance of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// The returned block is suitable for passing to the
+    /// `alloc`/`realloc` methods of this allocator.
+    ///
+    /// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
+    /// must be considered "currently allocated" and must be
+    /// acceptable input to methods such as `realloc` or `dealloc`,
+    /// *even if* `T` is a zero-sized type. In other words, if your
+    /// `Alloc` implementation overrides this method in a manner
+    /// that can return a zero-sized `ptr`, then all reallocation and
+    /// deallocation methods need to be similarly overridden to accept
+    /// such values as input.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `T` does not meet allocator's size or alignment constraints.
+    ///
+    /// For zero-sized `T`, may return either of `Ok` or `Err`, but
+    /// will *not* yield undefined behavior.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    fn alloc_one<T>(&mut self) -> Result<NonNull<T>, AllocErr>
+    where
+        Self: Sized,
+    {
+        let k = Layout::new::<T>();
+        if k.size() > 0 {
+            unsafe { self.alloc(k).map(|p| p.cast()) }
+        } else {
+            Err(AllocErr)
+        }
+    }
+
+    /// Deallocates a block suitable for holding an instance of `T`.
+    ///
+    /// The given block must have been produced by this allocator,
+    /// and must be suitable for storing a `T` (in terms of alignment
+    /// as well as minimum and maximum size); otherwise yields
+    /// undefined behavior.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure both:
+    ///
+    /// * `ptr` must denote a block of memory currently allocated via this allocator
+    ///
+    /// * the layout of `T` must *fit* that block of memory.
+    unsafe fn dealloc_one<T>(&mut self, ptr: NonNull<T>)
+    where
+        Self: Sized,
+    {
+        let k = Layout::new::<T>();
+        if k.size() > 0 {
+            self.dealloc(ptr.cast(), k);
+        }
+    }
+
+    /// Allocates a block suitable for holding `n` instances of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// The returned block is suitable for passing to the
+    /// `alloc`/`realloc` methods of this allocator.
+    ///
+    /// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
+    /// must be considered "currently allocated" and must be
+    /// acceptable input to methods such as `realloc` or `dealloc`,
+    /// *even if* `T` is a zero-sized type. In other words, if your
+    /// `Alloc` implementation overrides this method in a manner
+    /// that can return a zero-sized `ptr`, then all reallocation and
+    /// deallocation methods need to be similarly overridden to accept
+    /// such values as input.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `[T; n]` does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// For zero-sized `T` or `n == 0`, may return either of `Ok` or
+    /// `Err`, but will *not* yield undefined behavior.
+    ///
+    /// Always returns `Err` on arithmetic overflow.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    fn alloc_array<T>(&mut self, n: usize) -> Result<NonNull<T>, AllocErr>
+    where
+        Self: Sized,
+    {
+        match Layout::array::<T>(n) {
+            Ok(layout) if layout.size() > 0 => unsafe { self.alloc(layout).map(|p| p.cast()) },
+            _ => Err(AllocErr),
+        }
+    }
+
+    /// Reallocates a block previously suitable for holding `n_old`
+    /// instances of `T`, returning a block suitable for holding
+    /// `n_new` instances of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// The returned block is suitable for passing to the
+    /// `alloc`/`realloc` methods of this allocator.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * the layout of `[T; n_old]` must *fit* that block of memory.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `[T; n_new]` does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// For zero-sized `T` or `n_new == 0`, may return either of `Ok` or
+    /// `Err`, but will *not* yield undefined behavior.
+    ///
+    /// Always returns `Err` on arithmetic overflow.
+    ///
+    /// Clients wishing to abort computation in response to a
+    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn realloc_array<T>(
+        &mut self,
+        ptr: NonNull<T>,
+        n_old: usize,
+        n_new: usize,
+    ) -> Result<NonNull<T>, AllocErr>
+    where
+        Self: Sized,
+    {
+        match (Layout::array::<T>(n_old), Layout::array::<T>(n_new)) {
+            (Ok(ref k_old), Ok(ref k_new)) if k_old.size() > 0 && k_new.size() > 0 => {
+                debug_assert!(k_old.align() == k_new.align());
+                self.realloc(ptr.cast(), k_old.clone(), k_new.size())
+                    .map(NonNull::cast)
+            }
+            _ => Err(AllocErr),
+        }
+    }
+
+    /// Deallocates a block suitable for holding `n` instances of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure both:
+    ///
+    /// * `ptr` must denote a block of memory currently allocated via this allocator
+    ///
+    /// * the layout of `[T; n]` must *fit* that block of memory.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either `[T; n]` or the given
+    /// memory block does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// Always returns `Err` on arithmetic overflow.
+    unsafe fn dealloc_array<T>(&mut self, ptr: NonNull<T>, n: usize) -> Result<(), AllocErr>
+    where
+        Self: Sized,
+    {
+        match Layout::array::<T>(n) {
+            Ok(k) if k.size() > 0 => {
+                self.dealloc(ptr.cast(), k);
+                Ok(())
+            }
+            _ => Err(AllocErr),
+        }
+    }
+}