fully refactor runtime-std to use conditional compilation

substrate/runtime-std/src/lib.rs

@@ -1,7 +1,39 @@
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
+// Copyright 2017 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/>.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(not(feature = "std"), feature(lang_items))]
+#![cfg_attr(not(feature = "std"), feature(core_intrinsics))]
+#![cfg_attr(not(feature = "std"), feature(alloc))]
+
+#![cfg_attr(feature = "std", doc = "Polkadot runtime standard library as compiled when linked with Rust's standard library.")]
+#![cfg_attr(not(feature = "std"), doc = "Polkadot's runtime standard library as compiled without Rust's standard library.")]
+
+#[cfg(feature = "std")]
+include!("../with_std.rs");
+
+#[cfg(not(feature = "std"))]
+include!("../without_std.rs");
+
+
+
+/// Prelude of common useful imports.
+///
+/// This should include only things which are in the normal std prelude.
+pub mod prelude {
+	pub use ::vec::Vec;
+	pub use ::boxed::Box;
 }