Add new use_spin_nightly feature

.github/workflows/build.yml

@@ -105,7 +105,10 @@ jobs:
       run: cargo build --features alloc_ref
 
     - name: "Run cargo test with `alloc_ref` feature"
-      run: cargo test
+      run: cargo test --features alloc_ref
+
+    - name: "Run cargo test with `use_spin_nightly` feature"
+      run: cargo test --features use_spin_nightly
 
   check_formatting:
     name: "Check Formatting"

Cargo.toml

@@ -14,8 +14,9 @@ homepage = "http://os.phil-opp.com/kernel-heap.html#a-better-allocator"
 [features]
 default = ["use_spin", "const_mut_refs"]
 use_spin = ["spinning_top"]
+use_spin_nightly = ["use_spin", "spinning_top/nightly", "const_mut_refs"]
 alloc_ref = []
-const_mut_refs = ["spinning_top/nightly"]
+const_mut_refs = []
 
 [dependencies.spinning_top]
 version = "0.1.0"

Changelog.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+- Add new `use_spin_nightly` feature, which, together with `const_mut_refs`, makes the `empty` method of `LockedHeap` const ([#49](https://github.com/phil-opp/linked-list-allocator/pull/49))
+
 # 0.8.10 – 2020-12-28
 
 - Made hole module public for external uses ([#47](https://github.com/phil-opp/linked-list-allocator/pull/47))

README.md

@@ -32,6 +32,7 @@ pub fn init_heap() {
 
 - **`use_spin`** (default): Provide a `LockedHeap` type that implements the [`GlobalAlloc`] trait by using a spinlock.
 - **`const_mut_refs`** (default): Makes the `Heap::empty` function `const`; requires nightly Rust.
+- **`use_spin_nightly`**: Makes the `LockedHeap::empty` function `const`, automatically enables `const_mut_refs`; requires nightly Rust.
 - **`alloc_ref`**: Provide an implementation of the unstable [`AllocRef`] trait; requires nightly Rust.
     - Warning: The `AllocRef` trait is still regularly changed on the Rust side, so expect some regular breakage when using this feature.
 

src/lib.rs

@@ -155,8 +155,7 @@ impl Heap {
     }
 }
 
-#[cfg(feature = "alloc_ref")]
-#[cfg(feature = "use_spin")]
+#[cfg(all(feature = "alloc_ref", feature = "use_spin"))]
 unsafe impl Allocator for LockedHeap {
     fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         if layout.size() == 0 {
@@ -181,13 +180,13 @@ pub struct LockedHeap(Spinlock<Heap>);
 #[cfg(feature = "use_spin")]
 impl LockedHeap {
     /// Creates an empty heap. All allocate calls will return `None`.
-    #[cfg(feature = "const_mut_refs")]
+    #[cfg(feature = "use_spin_nightly")]
     pub const fn empty() -> LockedHeap {
         LockedHeap(Spinlock::new(Heap::empty()))
     }
 
     /// Creates an empty heap. All allocate calls will return `None`.
-    #[cfg(not(feature = "const_mut_refs"))]
+    #[cfg(not(feature = "use_spin_nightly"))]
     pub fn empty() -> LockedHeap {
         LockedHeap(Spinlock::new(Heap::empty()))
     }