Add ability to override lockfile from tools.nix

Author: apoelstra

tools.nix

@@ -30,10 +30,14 @@ rec {
     , src
     , cargoToml ? "Cargo.toml"
     , additionalCargoNixArgs ? [ ]
+    , overrideLockFile ? null
     }:
     let
       crateDir = dirOf (src + "/${cargoToml}");
-      vendor = internal.vendorSupport { inherit crateDir; };
+      vendor = overrideLockFile (internal.vendorSupport {
+        inherit crateDir;
+        additionalLockFiles = if overrideLockFile == null then [ ] else [ overrideLockFile ];
+      });
     in
     stdenv.mkDerivation {
       name = "${name}-crate2nix";
@@ -52,6 +56,11 @@ rec {
         export CARGO_HOME="$out/cargo"
         export HOME="$out"
 
+        ${if overrideLockFile == null then
+          ""
+        else
+          "cp ${overrideLockFile} ./Cargo.lock"}
+
         cp ${vendor.cargoConfig} $out/cargo/config
 
         crate_hashes="$out/crate-hashes.json"