Refactor the CLI checking of config arguments (#667)

This change moves the validation of the config file earlier in the setup
of the arg parser. The argparse library itself is validating whether the
file exists, so seems appropriate to also validate whether the file is a
proper toml config file early as well.

Signed-off-by: Eric Brown <eric.brown@securesauce.dev>

precli/cli/main.py

@@ -160,35 +160,34 @@ def setup_arg_parser():
     )
     args = parser.parse_args()
 
+    if args.config:
+        try:
+            args.config = tomllib.load(args.config)
+        except tomllib.TOMLDecodeError as err:
+            parser.error(
+                f"argument -c/--config: can't load '{args.config.name}': {err}"
+            )
+
     if not args.targets:
         parser.print_usage()
         sys.exit(2)
 
-    return parser, args
+    return args, args.config
 
 
-def load_config(
-    parser: ArgumentParser, config: dict, targets: list[str]
-) -> dict:
-    if config:
-        try:
-            return tomllib.load(config)
-        except tomllib.TOMLDecodeError as err:
-            parser.error(
-                f"argument -c/--config: can't load '{config.name}': {err}"
-            )
-    else:
-        default_confs = (".precli.toml", "precli.toml", "pyproject.toml")
-        for target in filter(os.path.isdir, targets):
-            for conf in default_confs:
-                path = pathlib.Path(target) / conf
-                try:
-                    if path.exists():
-                        with open(path, "rb") as f:
-                            return tomllib.load(f)
-                except tomllib.TOMLDecodeError:
-                    # TODO: Log but don't exit
-                    pass
+def find_config(targets: list[str]) -> dict:
+    default_confs = (".precli.toml", "precli.toml", "pyproject.toml")
+
+    for target in filter(os.path.isdir, targets):
+        for conf in default_confs:
+            path = pathlib.Path(target) / conf
+            try:
+                if path.exists():
+                    with open(path, "rb") as f:
+                        return tomllib.load(f)
+            except tomllib.TOMLDecodeError:
+                # TODO: Log but don't exit
+                pass
 
     return {}
 
@@ -377,10 +376,11 @@ def main():
     logging.getLogger("urllib3").setLevel(debug)
 
     # Setup the command line arguments
-    parser, args = setup_arg_parser()
+    args, config = setup_arg_parser()
 
-    # Load optional configuration file
-    config = load_config(parser, args.config, args.targets)
+    # Attempt to find config files if one not provided
+    if not config:
+        config = find_config(args.targets)
 
     # CLI enabled/disabled override any config in files
     config["enabled"] = (