rustc: Enable crosscompiling std crates

pkgs/development/compilers/rustc/beta.nix

@@ -1,4 +1,4 @@
-{ stdenv, callPackage, rustcStable }:
+{ stdenv, callPackage, rustcStable, targets ? [], targetToolchains ? [] }:
 
 callPackage ./generic.nix {
   shortVersion = "beta-1.10.0";
@@ -9,4 +9,6 @@ callPackage ./generic.nix {
   patches = [ ./patches/disable-lockfile-check.patch ] ++
     stdenv.lib.optional stdenv.needsPax ./patches/grsec.patch;
   rustc = rustcStable;
+  inherit targets;
+  inherit targetToolchains;
 }

pkgs/development/compilers/rustc/generic.nix

@@ -7,22 +7,10 @@
 , srcSha, srcRev
 , configureFlags ? []
 , patches
+, targets
+, targetToolchains
 } @ args:
 
-/* Rust's build process has a few quirks :
-
-- The Rust compiler is written is Rust, so it requires a bootstrap
-  compiler, which is downloaded during the build. To make the build
-  pure, we download it ourself before and put it where it is
-  expected. Once the language is stable (1.0) , we might want to
-  switch it to use nix's packaged rust compiler. This might not be possible
-  as the compiler is highly coupled to the bootstrap.
-
-NOTE : some derivation depend on rust. When updating this, please make
-sure those derivations still compile. (racer, for example).
-
-*/
-
 let
     version = if isRelease then
         "${shortVersion}"
@@ -35,15 +23,7 @@ let
 
     llvmShared = llvm.override { enableSharedLibraries = true; };
 
-    target = if stdenv.system == "i686-linux"
-      then "i686-unknown-linux-gnu"
-      else if stdenv.system == "x86_64-linux"
-      then "x86_64-unknown-linux-gnu"
-      else if stdenv.system == "i686-darwin"
-      then "i686-apple-darwin"
-      else if stdenv.system == "x86_64-darwin"
-      then "x86_64-apple-darwin"
-      else abort "no snapshot to bootstrap for this platform (missing target triple)";
+    target = builtins.replaceStrings [" "] [","] (builtins.toString targets);
 
     meta = with stdenv.lib; {
       homepage = http://www.rust-lang.org/;
@@ -75,9 +55,11 @@ stdenv.mkDerivation {
                 # ++ [ "--jemalloc-root=${jemalloc}/lib"
                 ++ [ "--default-linker=${stdenv.cc}/bin/cc" "--default-ar=${binutils.out}/bin/ar" ]
                 ++ stdenv.lib.optional (stdenv.cc.cc ? isClang) "--enable-clang"
+                ++ stdenv.lib.optional (targets != []) "--target=${target}"
                 ++ stdenv.lib.optional (!forceBundledLLVM) "--llvm-root=${llvmShared}";
 
   inherit patches;
+  passthru.target = target;
 
   postPatch = ''
     substituteInPlace src/rust-installer/gen-install-script.sh \
@@ -125,4 +107,5 @@ stdenv.mkDerivation {
   preCheck = "export TZDIR=${tzdata}/share/zoneinfo";
 
   doCheck = true;
+  dontSetConfigureCross = true;
 }

pkgs/development/compilers/rustc/head.nix

@@ -1,5 +1,5 @@
 # Please make sure to check if rustfmt still builds when updating nightly
-{ stdenv, callPackage, rustcStable }:
+{ stdenv, callPackage, rustcStable, targets ? [], targetToolchains ? [] }:
 
 callPackage ./generic.nix {
   shortVersion = "master-1.11.0";
@@ -10,4 +10,6 @@ callPackage ./generic.nix {
               ./patches/use-rustc-1.9.0.patch ] ++
     stdenv.lib.optional stdenv.needsPax ./patches/grsec.patch;
   rustc = rustcStable;
+  inherit targets;
+  inherit targetToolchains;
 }