Add optional allocator_api2, the std one

static-alloc/Cargo.toml

@@ -18,6 +18,7 @@ all-features = true
 [dependencies]
 alloc-traits = { path = "../alloc-traits", version = "0.1.0" }
 portable-atomic = { version = "1", optional = true, default-features = false }
+allocator-api2 = { version = "0.4", optional = true, default-features = false }
 
 [features]
 alloc = []

static-alloc/src/allocator_api2.rs

@@ -0,0 +1,90 @@
+use crate::bump::{Bump, BumpSlice, BumpView};
+
+use allocator_api2::alloc::{AllocError, Allocator, Layout};
+use core::ptr::NonNull;
+
+unsafe impl<T> Allocator for Bump<T> {
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        Allocator::allocate(&self.as_view(), layout)
+    }
+
+    unsafe fn deallocate(&self, _: NonNull<u8>, _: Layout) {}
+
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        // Safety: passing along requirements. These two allocators serve the same allocations, a
+        // property we permit for these two of our own types.
+        unsafe { Allocator::shrink(&self.as_view(), ptr, old_layout, new_layout) }
+    }
+}
+
+unsafe impl Allocator for BumpSlice {
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        Allocator::allocate(&self.as_view(), layout)
+    }
+
+    unsafe fn deallocate(&self, _: NonNull<u8>, _: Layout) {}
+
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        // Safety: passing along requirements. These two allocators serve the same allocations, a
+        // property we permit for these two of our own types.
+        unsafe { Allocator::shrink(&self.as_view(), ptr, old_layout, new_layout) }
+    }
+}
+
+unsafe impl Allocator for BumpView<'_> {
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        let len = layout.size();
+        match self.get_layout(layout) {
+            None => Err(AllocError),
+            Some(allocation) => Ok(NonNull::slice_from_raw_parts(allocation.ptr, len)),
+        }
+    }
+
+    unsafe fn deallocate(&self, _: NonNull<u8>, _: Layout) {}
+
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        debug_assert!(new_layout.size() <= old_layout.size());
+        let len = new_layout.size();
+
+        let offset = ptr.align_offset(new_layout.align());
+
+        if offset > 0 {
+            if old_layout
+                .size()
+                .checked_sub(offset)
+                .is_none_or(|n| n < len)
+            {
+                // Won't fit in-place. Sorry.
+                return Err(AllocError);
+            }
+
+            // Safety: in-bounds as we just verified that old layout has at least as many bytes as
+            // offset, and the caller was required to pass a live allocation with corresponding
+            // layout; implying that it also has that many bytes.
+            let dst = unsafe { ptr.byte_add(offset) };
+            // Safety: just verified that layout has at least `len` bytes after the offset so `dst`
+            // also has provenance according to the caller's requirements.
+            unsafe { ptr.copy_to(dst, len) };
+            dst
+        } else {
+            ptr
+        };
+
+        Ok(NonNull::slice_from_raw_parts(ptr, len))
+    }
+}

static-alloc/src/bump.rs

@@ -183,7 +183,7 @@ pub struct BumpSlice {
 ///
 /// Note: You might think that we can
 #[derive(Clone, Copy)]
-struct BumpView<'lt> {
+pub(crate) struct BumpView<'lt> {
     header: &'lt Header,
     storage: &'lt UnsafeCell<[MaybeUninit<u8>]>,
 }
@@ -564,7 +564,7 @@ impl<T> Bump<T> {
         self.header = Header::empty();
     }
 
-    fn as_view(&self) -> BumpView<'_> {
+    pub(crate) fn as_view(&self) -> BumpView<'_> {
         BumpView {
             header: &self.header,
             storage: {
@@ -1028,7 +1028,7 @@ impl BumpSlice {
         self.header = Header::empty();
     }
 
-    fn as_view(&self) -> BumpView<'_> {
+    pub(crate) fn as_view(&self) -> BumpView<'_> {
         BumpView {
             header: &self.header,
             storage: &self.storage,

static-alloc/src/lib.rs

@@ -47,6 +47,9 @@
 #[cfg(feature = "alloc")]
 extern crate alloc;
 
+#[cfg(feature = "allocator-api2")]
+mod allocator_api2;
+
 pub mod bump;
 pub use bump::Bump;
 pub mod leaked;