fully refactor runtime-std to use conditional compilation

substrate/wasm-runtime/pwasm-alloc/Cargo.toml

@@ -10,9 +10,14 @@ documentation = "https://paritytech.github.io/pwasm-std/pwasm_std/"
 description = "Parity WebAssembly standard library internal allocator"
 keywords = ["wasm", "parity", "webassembly", "blockchain"]
 categories = ["no-std", "embedded"]
+build = "build.rs"
 
 [dependencies]
 pwasm-libc = { path = "../pwasm-libc", version = "0.1" }
 
+[build-dependencies]
+rustc_version = "0.2"
+
 [features]
 strict = []
+nightly = []

substrate/wasm-runtime/pwasm-alloc/build.rs

@@ -0,0 +1,14 @@
+//! Set a nightly feature
+
+extern crate rustc_version;
+use rustc_version::{version, version_meta, Channel};
+
+fn main() {
+    // Assert we haven't travelled back in time
+    assert!(version().unwrap().major >= 1);
+
+    // Set cfg flags depending on release channel
+    if let Channel::Nightly = version_meta().unwrap().channel {
+        println!("cargo:rustc-cfg=feature=\"nightly\"");
+    }
+}

substrate/wasm-runtime/pwasm-alloc/src/lib.rs

@@ -2,29 +2,35 @@
 #![cfg_attr(feature = "strict", deny(warnings))]
 #![no_std]
 #![crate_type = "rlib"]
-#![feature(global_allocator)]
-#![feature(alloc)]
-#![feature(allocator_api)]
+#![cfg_attr(feature = "nightly", feature(global_allocator))]
+#![cfg_attr(feature = "nightly", feature(alloc))]
+#![cfg_attr(feature = "nightly", feature(allocator_api))]
 
 //! Custom allocator crate for wasm
 
-extern crate alloc;
-extern crate pwasm_libc;
-
-use alloc::heap::{Alloc, Layout, AllocErr};
-
 /// Wasm allocator
 pub struct WasmAllocator;
 
-unsafe impl<'a> Alloc for &'a WasmAllocator {
-	unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
-		Ok(pwasm_libc::malloc(layout.size()))
-	}
-
-	unsafe fn dealloc(&mut self, ptr: *mut u8, _layout: Layout) {
-		pwasm_libc::free(ptr)
-	}
-}
-
+#[cfg(feature = "nightly")]
 #[global_allocator]
 static ALLOCATOR: WasmAllocator = WasmAllocator;
+
+#[cfg(feature = "nightly")]
+mod __impl {
+	extern crate alloc;
+	extern crate pwasm_libc;
+
+	use self::alloc::heap::{Alloc, Layout, AllocErr};
+
+	use super::WasmAllocator;
+
+	unsafe impl<'a> Alloc for &'a WasmAllocator {
+		unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
+			Ok(pwasm_libc::malloc(layout.size()))
+		}
+
+		unsafe fn dealloc(&mut self, ptr: *mut u8, _layout: Layout) {
+			pwasm_libc::free(ptr)
+		}
+	}
+}