nix build: replace fetchCargoTarball with importCargoLock (servo#…

…31825)

[`importCargoLock`][1] allows us to use the existing Cargo.lock
file. This means we no longer need to update the sha256 hash
whenever the dependencies are upgraded. It also integrates
with nix's rustToolchain support via `cargoSetupHooks` and
automatically vendors the dependencies, allowing us to simplify
the logic for `filterlock` derivation.

[1]: https://github.com/NixOS/nixpkgs/blob/master/doc/languages-frameworks/rust.section.md#vendoring-of-dependencies-vendoring-of-dependencies

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

etc/shell.nix

@@ -96,27 +96,17 @@ stdenv.mkDerivation (androidEnvironment // rec {
     # all of Servo’s dependencies get pulled into the Nix store too, wasting over 1GB of disk space.
     # Filtering the lockfile to only the parts needed by crown saves space and builds faster.
     (let
-      vendorTarball = rustPlatform.fetchCargoTarball {
-        src = ../support/filterlock;
-        hash = "sha256-EBrL0/cEJfGIXUYqFiufRYFBAk5LSf0Cd/19+9m9JZI=";
-      };
-      vendorConfig = builtins.toFile "toml" ''
-        [source.crates-io]
-        replace-with = "vendor"
-        [source.vendor]
-        directory = "vendor"
-      '';
 
       # Build and run filterlock over the main Cargo.lock.
       filteredLockFile = (clangStdenv.mkDerivation {
         name = "lock";
         buildInputs = [ rustToolchain ];
+        nativeBuildInputs = [ rustPlatform.cargoSetupHook ];
         src = ../support/filterlock;
+        cargoDeps = rustPlatform.importCargoLock {
+          lockFile = ../support/filterlock/Cargo.lock;
+        };
         buildPhase = ''
-          tar xzf ${vendorTarball}
-          mv cargo-deps-vendor.tar.gz vendor
-          mkdir .cargo
-          cp -- ${vendorConfig} .cargo/config.toml
           > $out cargo run --offline -- ${../Cargo.lock} crown
         '';
         dontInstall = true;