feat(tvix/utils): Add mkCrate2nixCheck

This adds a function which can be used across the monorepo to create a
an extra CI step that checks whether the Cargo.nix file is up-to-date.

Change-Id: Idb8298b29ddc2ca5dff1facb1b9ed86a236ee66d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12227
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/utils.nix

@@ -1,4 +1,4 @@
-{ lib, depot, ... }:
+{ pkgs, lib, depot, ... }:
 
 {
   mkFeaturePowerset = { crateName, features, override ? { } }:
@@ -125,4 +125,27 @@
         src = depot.tvix.utils.filterRustCrateSrc { root = prev.src.origSrc; };
       };
     };
+
+  # This creates an extraStep in CI to check whether the Cargo.nix file is up-to-date.
+  mkCrate2nixCheck =
+    path: # The path to the Cargo.nix to be checked.
+    let
+      relCrateRoot = lib.removePrefix "./" (builtins.dirOf (lib.path.removePrefix depot.path.origSrc path));
+    in
+    {
+      label = "crate2nix check for ${relCrateRoot}";
+      needsOutput = true;
+      alwaysRun = true;
+      command = pkgs.writeShellScript "crate2nix-check-for-${lib.replaceStrings [ "/" ] ["-"] relCrateRoot}" ''
+        (cd $(git rev-parse --show-toplevel)/${relCrateRoot} &&
+          ${depot.tools.crate2nix-generate}/bin/crate2nix-generate &&
+          if [[ -n "$(git status --porcelain -unormal Cargo.nix)" ]]; then
+              echo "----------------------------------------------------------------------------------------------------"
+              echo "Cargo.nix needs to be updated, run 'mg run //tools/crate2nix-generate' in ${relCrateRoot}"
+              echo "----------------------------------------------------------------------------------------------------"
+              exit 1
+          fi
+        )
+      '';
+    };
 }