fix: bootstrap apps without version config

scripts/read_version.py

@@ -4,7 +4,9 @@
 from __future__ import annotations
 
 import argparse
+import re
 import subprocess
+import sys
 import tomllib
 
 
@@ -12,9 +14,35 @@ def parse_args() -> argparse.Namespace:
 	parser = argparse.ArgumentParser()
 	parser.add_argument("config_file")
 	parser.add_argument("--ref")
+	parser.add_argument("--fallback-version-file")
 	return parser.parse_args()
 
 
+def read_bootstrap_version(args: argparse.Namespace, config_error: KeyError) -> str:
+	if not args.ref or not args.fallback_version_file:
+		raise SystemExit(
+			f"Could not read tool.bumpversion.current_version from {args.config_file}: {config_error}"
+		) from config_error
+
+	try:
+		version_content = subprocess.check_output(
+			["git", "show", f"{args.ref}:{args.fallback_version_file}"],
+			text=True,
+		)
+	except (OSError, subprocess.CalledProcessError) as error:
+		raise SystemExit(
+			f"Could not load bootstrap version file {args.fallback_version_file}: {error}"
+		) from error
+
+	match = re.search(r'^__version__ = "(\d+\.\d+\.\d+)"$', version_content, re.MULTILINE)
+	if not match:
+		raise SystemExit(f"Could not read __version__ from bootstrap file {args.fallback_version_file}")
+
+	version = match.group(1)
+	print(f"Using bootstrap version {version} from {args.fallback_version_file}", file=sys.stderr)
+	return version
+
+
 def main() -> None:
 	args = parse_args()
 	try:
@@ -30,7 +58,9 @@ def main() -> None:
 
 	try:
 		version = tomllib.loads(content.decode())["tool"]["bumpversion"]["current_version"]
-	except (KeyError, TypeError, UnicodeDecodeError, tomllib.TOMLDecodeError) as error:
+	except KeyError as error:
+		version = read_bootstrap_version(args, error)
+	except (TypeError, UnicodeDecodeError, tomllib.TOMLDecodeError) as error:
 		raise SystemExit(
 			f"Could not read tool.bumpversion.current_version from {args.config_file}: {error}"
 		) from error