Detect subconfig loops and print clear error message

CHANGELOG.rst

@@ -20,6 +20,12 @@ Added
 - Support ``Deque`` and ``FrozenSet`` in type hints (`#905
   <https://github.com/omni-us/jsonargparse/pull/905>`__).
 
+Fixed
+^^^^^
+- Detect loops in config files that recursively load subconfig files and raise
+  an error showing the config chain instead of recursing indefinitely (`#910
+  <https://github.com/omni-us/jsonargparse/pull/910>`__).
+
 Changed
 ^^^^^^^
 - Docs now reference methods via the public ``ArgumentParser`` class instead of

jsonargparse/_actions.py

@@ -22,6 +22,7 @@
     import_object,
     indent_text,
     iter_to_set_str,
+    load_config_path_context,
     parse_value_or_config,
 )
 
@@ -251,7 +252,7 @@ def _load_config(self, value, parser):
             cfg, cfg_path = parse_value_or_config(value)
             if not isinstance(cfg, dict):
                 raise TypeError(f'Parser key "{self.dest}": Unable to load config "{value}"')
-            with change_to_path_dir(cfg_path):
+            with load_config_path_context(cfg_path), change_to_path_dir(cfg_path):
                 cfg = parser._apply_actions(cfg, parent_key=self.dest)
             return cfg
         except (TypeError,) + get_loader_exceptions() as ex:

jsonargparse/_core.py

@@ -95,6 +95,7 @@
     get_argument_group_class,
     get_private_kwargs,
     identity,
+    load_config_path_context,
     return_parser_if_captured,
 )
 
@@ -621,7 +622,7 @@ def parse_path(
             ArgumentError: If the parsing fails and ``exit_on_error=False``.
         """
         fpath = Path(cfg_path, mode=_get_config_read_mode())
-        with change_to_path_dir(fpath):
+        with load_config_path_context(fpath), change_to_path_dir(fpath):
             cfg_str = fpath.read_text()
             parsed_cfg = self.parse_string(
                 cfg_str=cfg_str,
@@ -1029,10 +1030,14 @@ def get_defaults(self, skip_validation: bool = False, **kwargs) -> Namespace:
 
         default_config_files = self._get_default_config_files()
         for default_config_file in default_config_files:
-            default_config_file_content = default_config_file.read_text()
-            if not default_config_file_content.strip():
-                continue
-            with change_to_path_dir(default_config_file), parser_context(parent_parser=self, parsing_defaults=True):
+            with (
+                load_config_path_context(default_config_file),
+                change_to_path_dir(default_config_file),
+                parser_context(parent_parser=self, parsing_defaults=True),
+            ):
+                default_config_file_content = default_config_file.read_text()
+                if not default_config_file_content.strip():
+                    continue
                 cfg_file = self._load_config_parser_mode(default_config_file_content, prev_cfg=cfg)
                 cfg = self.merge_config(cfg_file, cfg)
                 try:

jsonargparse/_typehints.py

@@ -88,6 +88,7 @@
     import_object,
     indent_text,
     iter_to_set_str,
+    load_config_path_context,
     object_path_serializer,
     parse_value_or_config,
     warning,
@@ -635,14 +636,14 @@ def _check_type(self, value, append=False, cfg=None, mode=None):
                     "logger": self.logger,
                 }
                 try:
-                    with change_to_path_dir(config_path):
+                    with load_config_path_context(config_path), change_to_path_dir(config_path):
                         val = adapt_typehints(val, self._typehint, **kwargs)
                 except ValueError as ex:
                     if orig_val == "-" and isinstance(getattr(ex, "parent", None), PathError):
                         raise ex
                     try:
                         if isinstance(orig_val, str):
-                            with change_to_path_dir(config_path):
+                            with load_config_path_context(config_path), change_to_path_dir(config_path):
                                 val = adapt_typehints(orig_val, self._typehint, default=self.default, **kwargs)
                             ex = None
                     except ValueError:

jsonargparse/_util.py

@@ -6,11 +6,14 @@
 import warnings
 from argparse import ArgumentError
 from collections import namedtuple
+from contextlib import contextmanager
+from contextvars import ContextVar
 from importlib import import_module
 from types import BuiltinFunctionType, FunctionType, ModuleType
 from typing import (
     Any,
     Callable,
+    Iterator,
     Optional,
     Type,
     Union,
@@ -36,6 +39,7 @@
 
 
 default_config_option_help = "Path to a configuration file."
+config_load_stack: ContextVar[tuple[tuple[str, str], ...]] = ContextVar("config_load_stack", default=())
 
 
 def argument_error(message: str, default_config_file: Optional[str] = None) -> ArgumentError:
@@ -45,6 +49,39 @@ def argument_error(message: str, default_config_file: Optional[str] = None) -> A
     return ex
 
 
+def _config_path_id(cfg_path: Path) -> tuple[str, str]:
+    path_id = cfg_path.absolute
+    if not (cfg_path.is_url or cfg_path.is_fsspec):
+        path_id = os.path.realpath(path_id)
+    return path_id, str(cfg_path)
+
+
+def _format_config_load_chain(stack: tuple[tuple[str, str], ...], path_id: tuple[str, str]) -> str:
+    chain = list(stack) + [path_id]
+    for num, (stack_path, _) in enumerate(chain):
+        if stack_path == path_id[0]:
+            chain = chain[num:]
+            break
+    return " -> ".join(display for _, display in chain)
+
+
+@contextmanager
+def load_config_path_context(cfg_path: Optional[Path]) -> Iterator[None]:
+    if cfg_path is None:
+        yield
+        return
+    path_id = _config_path_id(cfg_path)
+    stack = config_load_stack.get()
+    if path_id[0] in {path for path, _ in stack}:
+        chain = _format_config_load_chain(stack, path_id)
+        raise TypeError(f"Config file loop detected: {chain}")
+    token = config_load_stack.set(stack + (path_id,))
+    try:
+        yield
+    finally:
+        config_load_stack.reset(token)
+
+
 class JsonargparseWarning(UserWarning):
     pass
 
@@ -115,7 +152,7 @@ def parse_value_or_config(
         except TypeError:
             pass
         else:
-            with cfg_path.relative_path_context():
+            with load_config_path_context(cfg_path), cfg_path.relative_path_context():
                 value = load_value(cfg_path.read_text(), simple_types=simple_types)
     if type(value) is str and value.strip() != "":
         parsed_val = load_value(value, simple_types=simple_types)

jsonargparse_tests/test_actions.py

@@ -271,6 +271,26 @@ def test_action_parser_parse_path(composed_parsers):
     assert expected == cfg2.as_dict()
 
 
+def test_action_parser_config_loop(composed_parsers):
+    parser, yaml_main, yaml_inner2 = composed_parsers[:3]
+    yaml_main.write_text(json_or_yaml_dump({"inner2": "main.yaml"}))
+    with pytest.raises(ArgumentError) as ctx:
+        parser.parse_path(yaml_main)
+    ctx.match(r"Config file loop detected: .+main\.yaml -> main\.yaml")
+
+    yaml_main.write_text(json_or_yaml_dump({"inner2": "inner2.yaml"}))
+    yaml_inner2.write_text(json_or_yaml_dump({"inner3": "main.yaml"}))
+    with pytest.raises(ArgumentError) as ctx:
+        parser.parse_path(yaml_main)
+    ctx.match(r"Config file loop detected: .+main\.yaml -> inner2\.yaml -> main\.yaml")
+
+    yaml_main.write_text(json_or_yaml_dump({"inner2": "main.yaml"}))
+    parser.default_config_files = [str(yaml_main)]
+    with pytest.raises(ArgumentError) as ctx:
+        parser.parse_args([])
+    ctx.match(r"Config file loop detected: .+main\.yaml -> main\.yaml")
+
+
 def test_action_parser_parse_env_inner(composed_parsers):
     parser, _, yaml_inner2, yaml_inner3 = composed_parsers
     assert "opt2_env" == parser.parse_env({"LV1_INNER2__OPT2": "opt2_env"}).inner2.opt2