nix: commit missing file

nix/fetchcargo.nix

@@ -0,0 +1,35 @@
+{ stdenv, cacert, git, cargo, cargo-vendor }:
+{ name, src, sha256 }:
+stdenv.mkDerivation {
+  name = "${name}-vendor";
+  nativeBuildInputs = [ cacert git cargo cargo-vendor ];
+  inherit src;
+
+  phases = "unpackPhase patchPhase installPhase";
+
+  installPhase = ''
+    if [[ ! -f Cargo.lock ]]; then
+        echo
+        echo "ERROR: The Cargo.lock file doesn't exist"
+        echo
+        echo "Cargo.lock is needed to make sure that cargoSha256 doesn't change"
+        echo "when the registry is updated."
+        echo
+
+        exit 1
+    fi
+
+    export CARGO_HOME=$(mktemp -d cargo-home.XXX)
+
+    cargo vendor
+
+    cp -ar vendor $out
+  '';
+
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+  outputHash = sha256;
+
+  impureEnvVars = stdenv.lib.fetchers.proxyImpureEnvVars;
+  preferLocalBuild = true;
+}