[Nix-dev] $snapshot not evaluating

[stewart mackenzie]

Hello,

I've overriding rust to try get support for "cargo build
--target=arm-linux-androideabi"

The rust configureFlags in nixpkgs
https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/rustc/generic.nix#L122
there is a $snapshot which is not getting evaluated when I override it
here:
https://github.com/fractalide/fractalide/blob/master/build-support/rust-android.nix#L16

I know this because after experimenting with flags and noticing the output here:

example out put (where I'm messing with different flags)
configure flags:
--prefix=/nix/store/k6mp8qn4pxrqs38aqd4k4k1fmk4cjsc3-rustc-2016-01-10-gd70ab2b
--target=arm-unknown-linux-gnueabihf,x86_64-unknown-linux-gnu
--android-cross-path=/nix/store/81z3dixf4y8gkw0im5amjdcjs1a66mgv-ndk-standalone-toolchain
--enable-local-rust --local-rust-root=$snapshot --enable-rpath
--default-linker=/nix/store/bkllwvss62hch8vgxacnpdnvmlldwfxn-gcc-wrapper-4.9.3/bin/cc
--default-ar=/nix/store/iyw7cmmg2yi5cwc1pswfm0wrn1ssk1zh-binutils-2.23.1/bin/ar
--datadir=/nix/store/k6mp8qn4pxrqs38aqd4k4k1fmk4cjsc3-rustc-2016-01-10-gd70ab2b/share
--infodir=/nix/store/k6mp8qn4pxrqs38aqd4k4k1fmk4cjsc3-rustc-2016-01-10-gd70ab2b/share/info

Notice $snapshot isn't evaluated.

Is there a way for me to get $snapshot evaluated without copying over
all the code from nixpkgs yet simply overriding the configureFlags?
(example code I'd need to copy over
https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/rustc/generic.nix#L33-L119)

appreciated!

/sjm