Make inputs and backup_dir optional in the config file

They can come from -i and -o; missing ones were rejected as a bad configuration file (exit code 6).

simple_backup/simple_backup.py

@@ -946,19 +946,22 @@ def _read_config(config_file: str, user: str | None = None) -> ConfigArgs:
     config = configparser.ConfigParser(interpolation=None)
     config.read(config_file)
 
-    section = 'backup'
-
     # Allow compatibility with previous version of config file
-    try:
+    if config.has_section('backup'):
-        inputs = config.get(section, 'inputs')
+        section = 'backup'
-    except configparser.NoSectionError:
+    elif config.has_section('default'):
         section = 'default'
-        inputs = config.get(section, 'inputs')
+    else:
+        raise configparser.NoSectionError('backup')
 
-    config_args['inputs'] = list(set(_expand_inputs([i.strip() for i in inputs.split(',')], user)))
+    # inputs and backup_dir are optional, since -i and -o can give them. Missing ones are reported by check_params()
+    inputs = config.get(section, 'inputs', fallback=None)
+
+    if inputs is not None:
+        config_args['inputs'] = list(set(_expand_inputs([i.strip() for i in inputs.split(',')], user)))
 
     # '~' is expanded later, since for remote backups it refers to the home on the server
-    config_args['output'] = config.get(section, 'backup_dir')
+    config_args['output'] = config.get(section, 'backup_dir', fallback=None)
 
     exclude = config.get(section, 'exclude', fallback='')
     config_args['exclude'] = [e.strip() for e in exclude.split(',') if e.strip() != '']

tests/test_cli.py

@@ -170,6 +170,15 @@ ssh_keyfile=/keys/id
         assert b.keep == 0
         assert (b.ssh_host, b.ssh_user, b.ssh_keyfile) == ('cli-host', 'cli-user', '/cli/key')
 
+    def test_inputs_and_output_only_from_cli(self, run_cli: RunCli, tmp_path: Path) -> None:
+        config_file = tmp_path / 'simple_backup.conf'
+        config_file.write_text('[backup]\nkeep=3\n')
+
+        assert run_cli('-c', str(config_file), '-i', '/cli/in', '-o', '/cli/out') == 0
+
+        b = last_backup()
+        assert (b.inputs, b.output, b.keep) == (['/cli/in'], '/cli/out', 3)
+
     def test_ssh_host_and_user_from_cli_and_config(self, run_cli: RunCli, config: Callable[[str], str]) -> None:
         config_file = config('backup_dir=/backups\n[server]\nssh_user=user')
 

tests/test_config.py

@@ -224,9 +224,15 @@ backup_dir=/backups
         sb._read_config(config_file, USER)
 
 
+def test_inputs_and_backup_dir_optional(tmp_path: Path) -> None:
+    config_args = sb._read_config(write_config(tmp_path, '[backup]\nkeep=2\n'), USER)
+
+    assert config_args['inputs'] is None
+    assert config_args['output'] is None
+    assert config_args['keep'] == 2
+
+
 @pytest.mark.parametrize('text', [
-    '[backup]\nbackup_dir=/backups\n',
-    '[backup]\ninputs=/tmp\n',
     '[other]\ninputs=/tmp\n',
     'inputs=/tmp\n',
 ])