flake-parts/action-checkout/default.nix

@@ -0,0 +1,24 @@
+{
+  perSystem =
+    { config
+    , pkgs
+    , ...
+    }:
+    let
+      name = builtins.baseNameOf ./.;
+      script = config.writers.writePureShellScriptBin
+        name
+        [
+          pkgs.bash
+          pkgs.coreutils
+          pkgs.git
+          pkgs.openssh
+        ]
+        ''
+          bash ${./script.sh}
+        '';
+    in
+    {
+      packages.${name} = script;
+    };
+}

flake-parts/action-checkout/script.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# load BRANCH variable with default
+BRANCH=${BRANCH:-main}
+
+# load REPO_DIR variable with default
+export REPO_DIR=${REPO_DIR:-.}
+
+git clone --depth 1 --branch $BRANCH $REPO $REPO_DIR

flake.nix

@@ -42,6 +42,7 @@
       imports = [
         inputs.treefmt-nix.flakeModule
         inputs.clan-core.modules.flake-parts.writers
+        ./flake-parts/action-checkout
         ./flake-parts/action-flake-update
         ./flake-parts/action-create-pr
         ./targets/flake-module.nix