New rebuild mechanism

Put most of it as a flake app, so we can mess with it without relying on
`rb` being rebuilt. Also nom nom!

common/update-local-flakes.py

@@ -0,0 +1,62 @@
+import argparse
+import json
+import os
+import subprocess
+
+GET_INPUTS_CMD = [
+    "nix-instantiate",
+    "--eval",
+    "--json",  # This parser is stupid, better provide it with pre-eaten stuff
+    "--expr",
+    "builtins.fromJSON (builtins.toJSON (import ./flake.nix).inputs)",
+]
+
+
+def process_flake(flakeUri: str) -> None:
+    # get full path
+    flakeUri = os.path.normpath(flakeUri)
+    flakeFile = os.path.join(flakeUri, "flake.nix")
+    if not os.path.isfile(flakeFile):
+        raise FileNotFoundError(f"Flake not found: {flakeUri}")
+    # import dependencies
+    p = subprocess.run(GET_INPUTS_CMD, cwd=flakeUri, stdout=subprocess.PIPE)
+    deps = json.loads(p.stdout)
+    p.check_returncode()
+    # for each dependency
+    for dep_name, dep in deps.items():
+        dep_url = dep["url"]
+        # if not local path, continue
+        if not (
+            dep_url.startswith("path:")
+            or dep_url.startswith("git+file:")
+        ):
+            continue
+        if dep.get("flake", True):
+            #  get flake file corresponding
+            dep_path = dep_url.split(":")[1]
+            if not dep_path.startswith("/"):
+                dep_path = os.path.join(flakeUri, dep_path)
+            process_flake(dep_path)
+        # update lockfile
+        cmd = [
+            "nix",
+            "--extra-experimental-features",
+            "nix-command",
+            "--extra-experimental-features",
+            "flakes",
+            "flake",
+            "update",
+            dep_name,
+        ]
+        p = subprocess.run(cmd, cwd=flakeUri)
+        p.check_returncode()
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        description="Recursively update lockfiles "
+        "of flakes located on the system"
+    )
+    parser.add_argument("flake", help="Starting flake", default="/")
+    args = parser.parse_args()
+    process_flake(args.flake)