Implement Allocator APIs

Closes vorner#6

Cargo.toml

@@ -13,6 +13,11 @@ description = "Support for bumpalo in scoped threads & rayon"
 [dependencies]
 bumpalo = "~3"
 
+# This dependency provides a version of the unstable nightly Rust `Allocator`
+# trait on stable Rust. Enabling this feature means that `bumpalo` will
+# implement its `Allocator` trait.
+allocator-api2 = { version = "0.2.8", default-features = false, optional = true }
+
 [dev-dependencies]
 bumpalo = "~3"
 crossbeam-utils = "~0.8"
@@ -27,6 +32,6 @@ default = [
 collections = ["bumpalo/collections"]
 boxed = ["bumpalo/boxed"]
 allocator_api = ["bumpalo/allocator_api"]
-allocator-api2 = ["bumpalo/allocator-api2"]
+allocator-api2 = ["bumpalo/allocator-api2", "dep:allocator-api2"]
 serde = ["bumpalo/serde"]
 std = ["bumpalo/std"]

src/lib.rs

@@ -1,5 +1,6 @@
 #![doc(test(attr(deny(warnings))))]
 #![warn(missing_docs)]
+#![cfg_attr(feature = "allocator_api", feature(allocator_api))]
 
 //! The Bumpalo Herd
 //!
@@ -86,6 +87,12 @@ use std::mem::ManuallyDrop;
 use std::ptr::NonNull;
 use std::sync::Mutex;
 
+#[cfg(feature = "allocator_api")]
+use std::alloc::{AllocError, Allocator};
+
+#[cfg(all(feature = "allocator-api2", not(feature = "allocator_api")))]
+use allocator_api2::alloc::{AllocError, Allocator};
+
 use bumpalo::Bump;
 
 type HerdInner = Vec<Box<Bump>>;
@@ -263,6 +270,49 @@ impl Drop for Member<'_> {
     }
 }
 
+#[cfg(any(feature = "allocator_api", feature = "allocator-api2"))]
+unsafe impl Allocator for &Member<'_> {
+    #[inline]
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        self.as_bump().allocate(layout)
+    }
+
+    #[inline]
+    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
+        self.as_bump().deallocate(ptr, layout)
+    }
+
+    #[inline]
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        self.as_bump().shrink(ptr, old_layout, new_layout)
+    }
+
+    #[inline]
+    unsafe fn grow(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        self.as_bump().grow(ptr, old_layout, new_layout)
+    }
+
+    #[inline]
+    unsafe fn grow_zeroed(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        self.as_bump().grow_zeroed(ptr, old_layout, new_layout)
+    }
+}
+
 #[cfg(test)]
 // We disable stuff on that platform and are lazy to disable all the imports too, this is shorter.
 #[cfg_attr(all(miri, target_os = "windows"), allow(unused_imports))]