Refactor handling of inventory backend command line flag

This commit switches the inventory backend command line flag to the form
`--inventory-backend=<backend name>`. Additionally, we restrict the
allowed values for the flag to the known backends.

To ensure the allowed values for the command line flag, and the known
implementations are in sync, we introduce a dict holding the mapping
from flag values to `Inventory` subclasses.

Finally, we ensure that the selected backend is cached as a string in
`cached.args["inventory-backend"]`. Note that this is not how
`cached.args` is used otherwise, but since it's unlikely that there ever
will be a real command `inventory-backend`, this should be fine.

kapitan/cli.py

@@ -21,6 +21,7 @@
 from kapitan import cached, defaults, setup_logging
 from kapitan.initialiser import initialise_skeleton
 from kapitan.inputs.jsonnet import jsonnet_file
+from kapitan.inventory import AVAILABLE_BACKENDS
 from kapitan.lint import start_lint
 from kapitan.refs.base import RefController, Revealer
 from kapitan.refs.cmd_parser import handle_refs_command
@@ -103,12 +104,12 @@ def build_parser():
     subparser = parser.add_subparsers(help="commands", dest="subparser_name")
 
     inventory_backend_parser = argparse.ArgumentParser(add_help=False)
-    inventory_backend_group = inventory_backend_parser.add_argument_group("inventory_backend")
-    inventory_backend_group.add_argument(
-        "--reclass",
-        action="store_true",
-        default=from_dot_kapitan("inventory_backend", "reclass", False),
-        help="use reclass as inventory backend (default)",
+    inventory_backend_parser.add_argument(
+        "--inventory-backend",
+        action="store",
+        default=from_dot_kapitan("inventory_backend", "inventory", "reclass"),
+        choices=AVAILABLE_BACKENDS.keys(),
+        help="Select the inventory backend to use (default=reclass)",
     )
 
     eval_parser = subparser.add_parser("eval", aliases=["e"], help="evaluate jsonnet file")
@@ -663,6 +664,8 @@ def main():
     # cache args where key is subcommand
     assert "name" in args, "All cli commands must have provided default name"
     cached.args[args.name] = args
+    if "inventory_backend" in args:
+        cached.args["inventory-backend"] = args.inventory_backend
 
     if hasattr(args, "verbose") and args.verbose:
         setup_logging(level=logging.DEBUG, force=True)

kapitan/inventory/__init__.py

@@ -1,2 +1,10 @@
+from typing import Type
+
 from .inv_reclass import ReclassInventory
 from .inventory import Inventory
+
+# Dict mapping values for command line flag `--inventory-backend` to the
+# associated `Inventory` subclass.
+AVAILABLE_BACKENDS: dict[str, Type[Inventory]] = {
+    "reclass": ReclassInventory,
+}

kapitan/resources.py

@@ -22,7 +22,7 @@
 import kapitan.cached as cached
 from kapitan import __file__ as kapitan_install_path
 from kapitan.errors import CompileError, InventoryError, KapitanError
-from kapitan.inventory import Inventory, ReclassInventory
+from kapitan.inventory import Inventory, ReclassInventory, AVAILABLE_BACKENDS
 from kapitan.utils import PrettyDumper, deep_get, flatten_dict, render_jinja2_file, sha256_string
 
 logger = logging.getLogger(__name__)
@@ -316,13 +316,15 @@ def get_inventory(inventory_path) -> Inventory:
     if cached.inv and cached.inv.targets:
         return cached.inv
 
-    inventory_backend: Inventory = None
-
     # select inventory backend
-    if cached.args.get("inventory-backend") == "my-new-inventory":
-        logger.debug("Using my-new-inventory as inventory backend")
+    backend_id = cached.args.get("inventory-backend")
+    backend = AVAILABLE_BACKENDS.get(backend_id)
+    inventory_backend: Inventory = None
+    if backend != None:
+        logger.debug(f"Using {backend_id} as inventory backend")
+        inventory_backend = backend(inventory_path)
     else:
-        logger.debug("Using reclass as inventory backend")
+        logger.debug(f"Backend {backend_id} is unknown, falling back to reclass as inventory backend")
         inventory_backend = ReclassInventory(inventory_path)
 
     inventory_backend.search_targets()