add rust_environment

rust_environment/shell.nix

@@ -0,0 +1,30 @@
+{ pkgs ? import <nixpkgs> {} }:
+pkgs.mkShell {
+  NIX_ENFORCE_PURITY=0;
+  buildInputs = with pkgs; [
+    cargo
+    rustc
+  ];
+  shellHook = ''
+    function log_header {
+      echo -ne "==> \e[32m\e[1m$1\e[0m\n\n"
+    }
+    function log_subheader {
+      echo -ne "--> \e[33m\e[1m$1\e[0m\n\n"
+    }
+    function log {
+      echo -ne "    $1\n"
+    }
+
+    echo ""
+    log_header "rust_environment"
+    if [ -s Cargo.toml ]; then
+      log_subheader "found Cargo.toml, running 'cargo-build'"
+      cargo build
+      echo ""
+    fi
+    log_header "package versions"
+    log "$(rustc --version)"
+    log "$(cargo --version)"
+  '';
+}