Use feature cfg outside macro

cfg(feature="nightly") was being evaluated within the crate using the
lazy_static! macro. Instead we generate different macros depending on
the cfg.

Signed-off-by: Dan Schatzberg <[email protected]>

Author: dschatzberg

src/lib.rs

@@ -35,7 +35,7 @@ trait.
 
 Using the macro:
 
-```rust
+```ignore
 #[macro_use]
 extern crate lazy_static;
 
@@ -71,6 +71,7 @@ The `Deref` implementation uses a hidden static variable that is guarded by a at
 #![cfg_attr(feature="nightly", feature(const_fn, core_intrinsics))]
 #![crate_type = "dylib"]
 
+#[cfg(feature="nightly")]
 #[macro_export]
 macro_rules! lazy_static {
     ($(#[$attr:meta])* static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
@@ -94,7 +95,6 @@ macro_rules! lazy_static {
                     fn require_sync<T: Sync>(_: &T) { }
 
                     #[inline(always)]
-                    #[cfg(feature="nightly")]
                     unsafe fn __stability() -> &'static $T {
                         use std::cell::UnsafeCell;
 
@@ -112,8 +112,59 @@ macro_rules! lazy_static {
                         }
                     }
 
+                    let static_ref = __stability();
+                    require_sync(static_ref);
+                    static_ref
+                }
+            }
+        }
+        lazy_static!($($t)*);
+    };
+    (MAKE TY, PUB, $(#[$attr:meta])*, $N:ident) => {
+        #[allow(missing_copy_implementations)]
+        #[allow(non_camel_case_types)]
+        #[allow(dead_code)]
+        $(#[$attr])*
+        pub struct $N {__private_field: ()}
+        #[doc(hidden)]
+        pub static $N: $N = $N {__private_field: ()};
+    };
+    (MAKE TY, PRIV, $(#[$attr:meta])*, $N:ident) => {
+        #[allow(missing_copy_implementations)]
+        #[allow(non_camel_case_types)]
+        #[allow(dead_code)]
+        $(#[$attr])*
+        struct $N {__private_field: ()}
+        #[doc(hidden)]
+        static $N: $N = $N {__private_field: ()};
+    };
+    () => ()
+}
+
+#[cfg(not(feature="nightly"))]
+#[macro_export]
+macro_rules! lazy_static {
+    ($(#[$attr:meta])* static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
+        lazy_static!(PRIV, $(#[$attr])* static ref $N : $T = $e; $($t)*);
+    };
+    ($(#[$attr:meta])* pub static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
+        lazy_static!(PUB, $(#[$attr])* static ref $N : $T = $e; $($t)*);
+    };
+    ($VIS:ident, $(#[$attr:meta])* static ref $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
+        lazy_static!(MAKE TY, $VIS, $(#[$attr])*, $N);
+        impl ::std::ops::Deref for $N {
+            type Target = $T;
+            fn deref<'a>(&'a self) -> &'a $T {
+                #[inline(always)]
+                fn __static_ref_initialize() -> $T { $e }
+
+                unsafe {
+                    use std::sync::{Once, ONCE_INIT};
+
+                    #[inline(always)]
+                    fn require_sync<T: Sync>(_: &T) { }
+
                     #[inline(always)]
-                    #[cfg(not(feature="nightly"))]
                     unsafe fn __stability() -> &'static $T {
                         use std::mem::transmute;