Document the two relevant cargo features

Author: Kimundi

Cargo.toml

@@ -30,7 +30,7 @@ compiletest = ["compiletest_rs"]
 appveyor = { repository = "rust-lang-nursery/lazy-static.rs" }
 travis-ci = { repository = "rust-lang-nursery/lazy-static.rs" }
 
-# is-it-maintained-issue-resolution = { repository = "rust-lang-nursery/lazy-static.rs" }
-# is-it-maintained-open-issues = { repository = "rust-lang-nursery/lazy-static.rs" }
+is-it-maintained-issue-resolution = { repository = "rust-lang-nursery/lazy-static.rs" }
+is-it-maintained-open-issues = { repository = "rust-lang-nursery/lazy-static.rs" }
 
 maintenance = { status = "passively-maintained" }

src/core_lazy.rs

@@ -26,6 +26,7 @@ impl<T: Sync> Lazy<T> {
 }
 
 #[macro_export]
+#[doc(hidden)]
 macro_rules! __lazy_static_create {
     ($NAME:ident, $T:ty) => {
         static $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy::new();

src/lazy.rs

@@ -32,6 +32,7 @@ impl<T: Sync> Lazy<T> {
 unsafe impl<T: Sync> Sync for Lazy<T> {}
 
 #[macro_export]
+#[doc(hidden)]
 macro_rules! __lazy_static_create {
     ($NAME:ident, $T:ty) => {
         static mut $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy(0 as *const $T, $crate::lazy::ONCE_INIT);

src/lib.rs

@@ -86,7 +86,17 @@ fn main() {
 
 # Implementation details
 
-The `Deref` implementation uses a hidden static variable that is guarded by a atomic check on each access. On stable Rust, the macro may need to allocate each static on the heap.
+The `Deref` implementation uses a hidden static variable that is guarded by a atomic check on each access.
+
+# Cargo features
+
+This crate provides two cargo features:
+
+- `nightly`: This uses unstable language features only available on the nightly release channel for a more optimal implementation. In practice this currently means avoiding a heap allocation per static. This feature might get deprecated at a later point once all relevant optimizations are usable from stable.
+- `spin_no_std` (implies `nightly`): This allows using this crate in a no-std environment, by depending on the standalone `spin` crate.
+
+Both features depend on unstable language features, which means
+no guarantees can be made about them in regard to SemVer stability.
 
 */
 

src/nightly_lazy.rs

@@ -36,6 +36,7 @@ impl<T: Sync> Lazy<T> {
 unsafe impl<T: Sync> Sync for Lazy<T> {}
 
 #[macro_export]
+#[doc(hidden)]
 macro_rules! __lazy_static_create {
     ($NAME:ident, $T:ty) => {
         static mut $NAME: $crate::lazy::Lazy<$T> = $crate::lazy::Lazy(None, $crate::lazy::ONCE_INIT);