Support without_std env in environmental! (#110)

* Make environmental crate support without_std env.

* Small doc fixes.

substrate/environmental/Cargo.toml

@@ -2,3 +2,7 @@
 name = "environmental"
 version = "0.1.0"
 authors = ["Parity Technologies <[email protected]>"]
+
+[features]
+default = ["std"]
+std = []

substrate/environmental/src/lib.rs

@@ -40,12 +40,18 @@
 //! }
 //! ```
 
-use std::cell::RefCell;
-use std::thread::LocalKey;
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(not(feature = "std"), feature(const_fn))]
+
+#[cfg(feature = "std")]
+include!("../with_std.rs");
+
+#[cfg(not(feature = "std"))]
+include!("../without_std.rs");
 
 #[doc(hidden)]
 pub fn using<T: ?Sized, R, F: FnOnce() -> R>(
-	global: &'static LocalKey<RefCell<Option<*mut T>>>,
+	global: &'static imp::LocalKey<imp::RefCell<Option<*mut T>>>,
 	protected: &mut T,
 	f: F
 ) -> R {
@@ -59,13 +65,13 @@ pub fn using<T: ?Sized, R, F: FnOnce() -> R>(
 	global.with(|r| {
 		let original = {
 			let mut global = r.borrow_mut();
-			::std::mem::replace(&mut *global, Some(protected as _))
+			imp::replace(&mut *global, Some(protected as _))
 		};
 
 		// even if `f` panics the original will be replaced.
 		struct ReplaceOriginal<'a, T: 'a + ?Sized> {
 			original: Option<*mut T>,
-			global: &'a RefCell<Option<*mut T>>,
+			global: &'a imp::RefCell<Option<*mut T>>,
 		}
 
 		impl<'a, T: 'a + ?Sized> Drop for ReplaceOriginal<'a, T> {
@@ -85,7 +91,7 @@ pub fn using<T: ?Sized, R, F: FnOnce() -> R>(
 
 #[doc(hidden)]
 pub fn with<T: ?Sized, R, F: FnOnce(&mut T) -> R>(
-	global: &'static LocalKey<RefCell<Option<*mut T>>>,
+	global: &'static imp::LocalKey<imp::RefCell<Option<*mut T>>>,
 	mutator: F,
 ) -> Option<R> {
 	global.with(|r| unsafe {
@@ -104,6 +110,7 @@ pub fn with<T: ?Sized, R, F: FnOnce(&mut T) -> R>(
 /// Declare a new global reference module whose underlying value does not contain references.
 ///
 /// Will create a module of a given name that contains two functions:
+///
 /// * `pub fn using<R, F: FnOnce() -> R>(protected: &mut $t, f: F) -> R`
 ///   This executes `f`, returning its value. During the call, the module's reference is set to
 ///   be equal to `protected`.
@@ -163,7 +170,7 @@ macro_rules! environmental {
 		#[allow(non_camel_case_types)]
 		struct $name { __private_field: () }
 
-		thread_local!(static GLOBAL: ::std::cell::RefCell<Option<*mut $t>>
+		thread_local_impl!(static GLOBAL: ::std::cell::RefCell<Option<*mut $t>>
 			= ::std::cell::RefCell::new(None));
 
 		impl $name {
@@ -187,8 +194,8 @@ macro_rules! environmental {
 		#[allow(non_camel_case_types)]
 		struct $name { __private_field: () }
 
-		thread_local!(static GLOBAL: ::std::cell::RefCell<Option<*mut ($t + 'static)>>
-			= ::std::cell::RefCell::new(None));
+		thread_local_impl!(static GLOBAL: $crate::imp::RefCell<Option<*mut ($t + 'static)>>
+			= $crate::imp::RefCell::new(None));
 
 		impl $name {
 			#[allow(unused_imports)]
@@ -198,7 +205,7 @@ macro_rules! environmental {
 				f: F
 			) -> R {
 				let lifetime_extended = unsafe {
-					::std::mem::transmute::<&mut $t, &mut ($t + 'static)>(protected)
+					$crate::imp::transmute::<&mut $t, &mut ($t + 'static)>(protected)
 				};
 				$crate::using(&GLOBAL, lifetime_extended, f)
 			}

substrate/environmental/with_std.rs

@@ -0,0 +1,31 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+#[doc(hidden)]
+pub mod imp {
+	pub use std::cell::RefCell;
+	pub use std::thread::LocalKey;
+	pub use std::mem::transmute;
+	pub use std::mem::replace;
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! thread_local_impl {
+	($(#[$attr:meta])* static $name:ident: $t:ty = $init:expr) => (
+		thread_local!($(#[$attr])* static $name: $t = $init);
+	);
+}

substrate/environmental/without_std.rs

@@ -0,0 +1,69 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+#[doc(hidden)]
+pub mod imp {
+	pub use core::cell::RefCell;
+	pub use core::mem::transmute;
+	pub use core::mem::replace;
+
+	// This code is a simplified version of [`LocalKey`] and it's wasm32 specialization: [`statik::Key`].
+	// [`LocalKey`]: https://github.com/alexcrichton/rust/blob/98931165a23a1c2860d99759385f45d6807c8982/src/libstd/thread/local.rs#L89
+	// [`statik::Key`]: https://github.com/alexcrichton/rust/blob/98931165a23a1c2860d99759385f45d6807c8982/src/libstd/thread/local.rs#L310-L312
+
+	pub struct LocalKey<T: 'static> {
+		pub init: fn() -> T,
+		pub inner: RefCell<Option<T>>,
+	}
+
+	// This is safe as long there is no threads in wasm32.
+	unsafe impl<T: 'static> ::core::marker::Sync for LocalKey<T> { }
+
+	impl<T: 'static> LocalKey<T> {
+		pub const fn new(init: fn() -> T) -> LocalKey<T> {
+			LocalKey {
+				init,
+				inner: RefCell::new(None),
+			}
+		}
+
+		pub fn with<F, R>(&'static self, f: F) -> R
+		where F: FnOnce(&T) -> R
+		{
+			if self.inner.borrow().is_none() {
+				let v = (self.init)();
+				*self.inner.borrow_mut() = Some(v);
+			}
+			// This code can't panic because:
+			// 1. `inner` can be borrowed mutably only once at the initialization time.
+			// 2. After the initialization `inner` is always `Some`.
+			f(&*self.inner.borrow().as_ref().unwrap())
+		}
+	}
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! thread_local_impl {
+	($(#[$attr:meta])* static $name:ident: $t:ty = $init:expr) => (
+		$(#[$attr])*
+		static $name: $crate::imp::LocalKey<$t> = {
+			fn __init() -> $t { $init }
+
+			$crate::imp::LocalKey::new(__init)
+		};
+	);
+}