Repository: omni-us/jsonargparse

Issue:
Support for generic dataclasses
## 🚀 Feature request

Add support for generic dataclasses in `ArgumentParser`.

### Motivation

I often use generic dataclasses as configuration objects in libraries code. When building a CLI application, I would like to reuse these configurations to build a specialized parser.
Currently if a generic dataclass is used as a subparser, the argument parsing complains that all parameters are not typed and crashes.

```python
from dataclasses import dataclass
from typing import Generic, TypeVar

from jsonargparse import ActionConfigFile, ArgumentParser

T = TypeVar("T")

# This is generic library code
@dataclass
class SubConfig(Generic[T]):
    generic: T
    a: int = 1
    b: float = 2.0

# This is CLI-specific
@dataclass
class Config:
    subconfig: SubConfig[int]


if __name__ == "__main__":
    parser = ArgumentParser(print_config="--print-config")
    parser.add_argument("--load", action=ActionConfigFile, help="Path to a YAML configuration")
    parser.add_dataclass_arguments(Config, "config")
    parser.parse_args()
```

```bash
$ python mre_jsonargparse.py --print-config
Traceback (most recent call last):
  File "/Users/bilelomrani/Documents/ILLUIN.nosync/instructions-finetuning/mre_jsonargparse.py", line 24, in <module>
    parser.add_dataclass_arguments(Config, "config")
  File "/Users/bilelomrani/Documents/ILLUIN.nosync/instructions-finetuning/.venv/lib/python3.10/site-packages/jsonargparse/_signatures.py", line 435, in add_dataclass_arguments
    self._add_signature_parameter(
  File "/Users/bilelomrani/Documents/ILLUIN.nosync/instructions-finetuning/.venv/lib/python3.10/site-packages/jsonargparse/_signatures.py", line 381, in _add_signature_parameter
    raise ValueError(
ValueError: With fail_untyped=True, all mandatory parameters must have a supported type. Parameter 'subconfig' from '__main__.Config.__init__' does not specify a type.
```

With `fail_untyped=False`, the printed config is empty.

### Pitch

Would be cool if `parser.add_dataclass_arguments` would work with generic dataclasses and would generate a specialized subparser (in the case of my example, adding an `int` validator to `config.subconfig.generic`).


Discussion:
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Patch coverage: **`100.00%`** and project coverage change: **`-0.02%`** :warning:
> Comparison is base [(`a14d3d4`)](https://app.codecov.io/gh/omni-us/jsonargparse/commit/a14d3d483b722049818db694bb03e22ec24df726?el=desc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=omni-us) 100.00% compared to head [(`a71f9e4`)](https://app.codecov.io/gh/omni-us/jsonargparse/pull/378?src=pr&el=desc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=omni-us) 99.98%.

<details><summary>Additional details and impacted files</summary>


```diff
@@             Coverage Diff             @@
##              main     #378      +/-   ##
===========================================
- Coverage   100.00%   99.98%   -0.02%     
===========================================
  Files           21       21              
  Lines         5712     5734      +22     
===========================================
+ Hits          5712     5733      +21     
- Misses           0        1       +1     
```

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|---|---|---|
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</details>

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Patch:
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 3e4a477..7958e8f 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -15,6 +15,11 @@ paths are considered internals and can change in minor and patch releases.
 v4.25.0 (2023-09-??)
 --------------------
 
+Added
+^^^^^
+- Support for user-defined generic types (`#366
+  <https://github.com/omni-us/jsonargparse/issues/366>`__).
+
 Fixed
 ^^^^^
 - ``--print_config`` fails when parser has shallow links.
diff --git a/DOCUMENTATION.rst b/DOCUMENTATION.rst
index f68a386..46dc308 100644
--- a/DOCUMENTATION.rst
+++ b/DOCUMENTATION.rst
@@ -407,6 +407,9 @@ Some notes about this support are:
   see :ref:`dataclass-like`. If a dataclass is mixed inheriting from a normal
   class, it is considered a subclass type instead of a dataclass.
 
+- User-defined ``Generic`` types are supported. For more details see
+  :ref:`generic-types`.
+
 - `Pydantic types <https://docs.pydantic.dev/usage/types/#pydantic-types>`__ are
   supported. There might be edge cases which don't work as expected. Please
   report any encountered issues.
@@ -876,6 +879,39 @@ structure.
       number: 8
       accepted: true
 
+.. _generic-types:
+
+Generic types
+-------------
+
+Classes that inherit from ``typing.Generic``, also known as `user-defined
+generic types
+<https://docs.python.org/3/library/typing.html#user-defined-generic-types>`__,
+are supported. Take for example a point in 2D:
+
+.. testsetup:: generic_types
+
+    parser = ArgumentParser()
+
+.. testcode:: generic_types
+
+    from typing import Generic, TypeVar
+
+    Number = TypeVar("Number", float, complex)
+
+    @dataclass
+    class Point2d(Generic[Number]):
+        x: Number = 0.0
+        y: Number = 0.0
+
+Parsing complex-valued points would be:
+
+.. doctest:: generic_types
+
+    >>> parser.add_argument("--point", type=Point2d[complex])  # doctest: +IGNORE_RESULT
+    >>> parser.parse_args(["--point.x=(1+2j)"]).point
+    Namespace(x=(1+2j), y=0.0)
+
 
 .. _callable-type:
 
diff --git a/README.rst b/README.rst
index a06ac4b..c1c7aa2 100644
--- a/README.rst
+++ b/README.rst
@@ -63,9 +63,9 @@ high-quality code**. It encompasses numerous powerful features, some unique to
 
 Other notable features include:
 
-- **Extensive type hint support:** nested types (union, tuple, etc.),
-  containers (list, dict, etc.), restricted types (regex, numbers), paths, URLs,
-  types from stubs (``*.pyi``), future annotations (PEP `563
+- **Extensive type hint support:** nested types (union, optional), containers
+  (list, dict, etc.), user-defined generics, restricted types (regex, numbers),
+  paths, URLs, types from stubs (``*.pyi``), future annotations (PEP `563
   <https://peps.python.org/pep-0563/>`__), and backports (PEPs `604
   <https://peps.python.org/pep-0604>`__/`585
   <https://peps.python.org/pep-0585>`__).
diff --git a/jsonargparse/_common.py b/jsonargparse/_common.py
index 348f523..06053c9 100644
--- a/jsonargparse/_common.py
+++ b/jsonargparse/_common.py
@@ -3,7 +3,7 @@ import inspect
 import sys
 from contextlib import contextmanager
 from contextvars import ContextVar
-from typing import Dict, Optional, Tuple, Type, TypeVar, Union
+from typing import Dict, Generic, Optional, Tuple, Type, TypeVar, Union, _GenericAlias  # type: ignore
 
 from ._namespace import Namespace
 from ._type_checking import ArgumentParser
@@ -70,12 +70,22 @@ def is_final_class(cls) -> bool:
     return getattr(cls, "__final__", False)
 
 
+def is_generic_class(cls) -> bool:
+    return isinstance(cls, _GenericAlias) and getattr(cls, "__module__", "") != "typing"
+
+
+def get_generic_origin(cls):
+    return cls.__origin__ if is_generic_class(cls) else cls
+
+
 def is_dataclass_like(cls) -> bool:
+    if is_generic_class(cls):
+        return is_dataclass_like(cls.__origin__)
     if not inspect.isclass(cls):
         return False
     if is_final_class(cls):
         return True
-    classes = [c for c in inspect.getmro(cls) if c != object]
+    classes = [c for c in inspect.getmro(cls) if c not in {object, Generic}]
     all_dataclasses = all(dataclasses.is_dataclass(c) for c in classes)
     from ._optionals import attrs_support, pydantic_support
 
diff --git a/jsonargparse/_parameter_resolvers.py b/jsonargparse/_parameter_resolvers.py
index a2df528..a53513b 100644
--- a/jsonargparse/_parameter_resolvers.py
+++ b/jsonargparse/_parameter_resolvers.py
@@ -11,7 +11,7 @@ from dataclasses import dataclass
 from functools import partial
 from typing import Any, Callable, Dict, List, Optional, Tuple, Type, Union
 
-from ._common import is_dataclass_like, is_subclass
+from ._common import get_generic_origin, is_dataclass_like, is_generic_class, is_subclass
 from ._optionals import parse_docs
 from ._postponed_annotations import evaluate_postponed_annotations
 from ._stubs_resolver import get_stub_types
@@ -283,9 +283,28 @@ def get_signature_parameters_and_indexes(component, parent, logger):
         )
     evaluate_postponed_annotations(params, signature_source, parent, logger)
     stubs = get_stub_types(params, signature_source, parent, logger)
+    replace_generic_type_vars(params, parent)
     return params, args_idx, kwargs_idx, doc_params, stubs
 
 
+def replace_generic_type_vars(params: ParamList, parent) -> None:
+    if is_generic_class(parent) and parent.__args__ and getattr(parent.__origin__, "__parameters__", None):
+        type_vars = dict(zip(parent.__origin__.__parameters__, parent.__args__))
+
+        def replace_type_vars(annotation):
+            if annotation in type_vars:
+                return type_vars[annotation]
+            if getattr(annotation, "__args__", None):
+                origin = annotation.__origin__
+                if sys.version_info < (3, 10) and getattr(origin, "__module__", "") != "typing":
+                    origin = getattr(__import__("typing"), origin.__name__.capitalize(), origin)
+                return origin[tuple(replace_type_vars(a) for a in annotation.__args__)]
+            return annotation
+
+        for param in params:
+            param.annotation = replace_type_vars(param.annotation)
+
+
 def add_stub_types(stubs: Optional[Dict[str, Any]], params: ParamList, component) -> None:
     if not stubs:
         return
@@ -380,7 +399,7 @@ def group_parameters(params_list: List[ParamList]) -> ParamList:
 
 
 def has_dunder_new_method(cls, attr_name):
-    classes = inspect.getmro(cls)[1:]
+    classes = inspect.getmro(get_generic_origin(cls))[1:]
     return (
         attr_name == "__init__"
         and cls.__new__ is not object.__new__
@@ -424,13 +443,13 @@ def get_component_and_parent(
     if is_subclass(function_or_class, ClassFromFunctionBase) and method_or_property in {None, "__init__"}:
         function_or_class = function_or_class.wrapped_function  # type: ignore
         method_or_property = None
-    elif inspect.isclass(function_or_class) and method_or_property is None:
+    elif inspect.isclass(get_generic_origin(function_or_class)) and method_or_property is None:
         method_or_property = "__init__"
     elif method_or_property and not isinstance(method_or_property, str):
         method_or_property = method_or_property.__name__
     parent = component = None
     if method_or_property:
-        attr = inspect.getattr_static(function_or_class, method_or_property)
+        attr = inspect.getattr_static(get_generic_origin(function_or_class), method_or_property)
         if is_staticmethod(attr):
             component = getattr(function_or_class, method_or_property)
             return component, parent, method_or_property
diff --git a/jsonargparse/_signatures.py b/jsonargparse/_signatures.py
index 6e6bd31..ba5731f 100644
--- a/jsonargparse/_signatures.py
+++ b/jsonargparse/_signatures.py
@@ -8,7 +8,7 @@ from contextlib import suppress
 from typing import Any, Callable, List, Optional, Set, Tuple, Type, Union
 
 from ._actions import _ActionConfigLoad
-from ._common import get_class_instantiator, is_dataclass_like, is_subclass
+from ._common import get_class_instantiator, get_generic_origin, is_dataclass_like, is_subclass
 from ._optionals import get_doc_short_description, pydantic_support
 from ._parameter_resolvers import (
     ParamData,
@@ -72,7 +72,7 @@ class SignatureArguments(LoggerProperty):
             ValueError: When not given a class.
             ValueError: When there are required parameters without at least one valid type.
         """
-        if not inspect.isclass(theclass):
+        if not inspect.isclass(get_generic_origin(theclass)):
             raise ValueError(f'Expected "theclass" parameter to be a class type, got: {theclass}.')
         if default and not (isinstance(default, LazyInitBaseClass) and isinstance(default, theclass)):
             raise ValueError(f'Expected "default" parameter to be a lazy instance of the class, got: {default}.')
@@ -133,7 +133,7 @@ class SignatureArguments(LoggerProperty):
             ValueError: When not given a class or the name of a method of the class.
             ValueError: When there are required parameters without at least one valid type.
         """
-        if not inspect.isclass(theclass):
+        if not inspect.isclass(get_generic_origin(theclass)):
             raise ValueError('Expected "theclass" argument to be a class object.')
         if not hasattr(theclass, themethod) or not callable(getattr(theclass, themethod)):
             raise ValueError('Expected "themethod" argument to be a callable member of the class.')
diff --git a/jsonargparse/_util.py b/jsonargparse/_util.py
index 7d4c33a..e5b8eb9 100644
--- a/jsonargparse/_util.py
+++ b/jsonargparse/_util.py
@@ -30,7 +30,7 @@ from typing import (
     get_type_hints,
 )
 
-from ._common import ClassType, is_subclass, parser_capture, parser_context
+from ._common import ClassType, get_generic_origin, is_subclass, parser_capture, parser_context
 from ._deprecated import PathDeprecations
 from ._loaders_dumpers import json_dump, load_value
 from ._optionals import (
@@ -215,6 +215,7 @@ def get_module_var_path(module_path: str, value: Any) -> Optional[str]:
 def get_import_path(value: Any) -> Optional[str]:
     """Returns the shortest dot import path for the given object."""
     path = None
+    value = get_generic_origin(value)
     module_path = getattr(value, "__module__", None)
     qualname = getattr(value, "__qualname__", "")
 


Test patch:
diff --git a/jsonargparse_tests/test_dataclass_like.py b/jsonargparse_tests/test_dataclass_like.py
index 5cf262a..3c0622e 100644
--- a/jsonargparse_tests/test_dataclass_like.py
+++ b/jsonargparse_tests/test_dataclass_like.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import dataclasses
-from typing import Any, Dict, List, Optional, Union
+from typing import Any, Dict, Generic, List, Optional, Tuple, TypeVar, Union
 from unittest.mock import patch
 
 import pytest
@@ -385,6 +385,40 @@ def test_dataclass_in_list_type(parser):
     assert isinstance(init.list[1], Data)
 
 
+T = TypeVar("T", int, float)
+
+
+@dataclasses.dataclass
+class GenericData(Generic[T]):
+    g1: T
+    g2: Tuple[T, T]
+    g3: Union[str, T]
+    g4: Dict[str, Union[T, bool]]
+
+
+def test_generic_dataclass(parser):
+    parser.add_argument("--data", type=GenericData[int])
+    help_str = get_parser_help(parser).lower()
+    assert "--data.g1 g1          (required, type: int)" in help_str
+    assert "--data.g2 [item,...]  (required, type: tuple[int, int])" in help_str
+    assert "--data.g3 g3          (required, type: union[str, int])" in help_str
+    assert "--data.g4 g4          (required, type: dict[str, union[int, bool]])" in help_str
+
+
+@dataclasses.dataclass
+class SpecificData:
+    y: GenericData[float]
+
+
+def test_nested_generic_dataclass(parser):
+    parser.add_dataclass_arguments(SpecificData, "x")
+    help_str = get_parser_help(parser).lower()
+    assert "--x.y.g1 g1          (required, type: float)" in help_str
+    assert "--x.y.g2 [item,...]  (required, type: tuple[float, float])" in help_str
+    assert "--x.y.g3 g3          (required, type: union[str, float])" in help_str
+    assert "--x.y.g4 g4          (required, type: dict[str, union[float, bool]])" in help_str
+
+
 # final classes tests
 
 
diff --git a/jsonargparse_tests/test_signatures.py b/jsonargparse_tests/test_signatures.py
index b251e96..f10ff1e 100644
--- a/jsonargparse_tests/test_signatures.py
+++ b/jsonargparse_tests/test_signatures.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from pathlib import Path
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import Any, Dict, Generic, List, Optional, Tuple, TypeVar, Union
 from unittest.mock import patch
 
 import pytest
@@ -391,6 +391,22 @@ def test_add_class_custom_instantiator(parser):
     assert init.a.call == "custom"
 
 
+X = TypeVar("X")
+Y = TypeVar("Y")
+
+
+class WithGenerics(Generic[X, Y]):
+    def __init__(self, a: X, b: Y):
+        self.a = a
+        self.b = b
+
+
+def test_add_class_generics(parser):
+    parser.add_class_arguments(WithGenerics[int, complex], "p")
+    cfg = parser.parse_args(["--p.a=5", "--p.b=(6+7j)"])
+    assert cfg.p == Namespace(a=5, b=6 + 7j)
+
+
 # add_method_arguments tests