support stable Rust, introduce a new feature 'const_fn' on nightly

Author: wangrunji0408

.github/workflows/rust.yml

@@ -13,6 +13,7 @@ jobs:
     strategy:
       matrix:
         rust: 
+        - stable
         - nightly-2020-09-24
 
     steps:

Cargo.toml

@@ -13,6 +13,7 @@ license = "MIT"
 [features]
 default = ["use_spin"]
 use_spin = ["spin"]
+const_fn = []
 
 [dependencies.spin]
 version = "0.5"

README.md

@@ -28,6 +28,13 @@ unsafe {
 
 You can also use `FrameAllocator` and `LockedHeapWithRescue`, see their documentation for usage.
 
+## Features
+
+- **`use_spin`** (default): Provide a `LockedHeap` type that implements the [`GlobalAlloc`] trait by using a spinlock.
+- **`const_fn`** (nightly only): Provide const fn version of `LockedHeapWithRescue::new`.
+
+[`GlobalAlloc`]: https://doc.rust-lang.org/nightly/core/alloc/trait.GlobalAlloc.html
+
 ## License
 
 Some code comes from phil-opp's linked-list-allocator.

src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(const_mut_refs, const_fn_fn_ptr_basics)]
+#![cfg_attr(feature = "const_fn", feature(const_mut_refs, const_fn_fn_ptr_basics))]
 #![no_std]
 
 #[cfg(test)]
@@ -287,12 +287,22 @@ pub struct LockedHeapWithRescue {
 #[cfg(feature = "use_spin")]
 impl LockedHeapWithRescue {
     /// Creates an empty heap
+    #[cfg(feature = "const_fn")]
     pub const fn new(rescue: fn(&mut Heap)) -> LockedHeapWithRescue {
         LockedHeapWithRescue {
             inner: Mutex::new(Heap::new()),
             rescue,
         }
     }
+
+    /// Creates an empty heap
+    #[cfg(not(feature = "const_fn"))]
+    pub fn new(rescue: fn(&mut Heap)) -> LockedHeapWithRescue {
+        LockedHeapWithRescue {
+            inner: Mutex::new(Heap::new()),
+            rescue,
+        }
+    }
 }
 
 #[cfg(feature = "use_spin")]