Cannot parse a list of unions of two different dataclasses

[mnidza]

🐛 Bug report

I am getting an error when parsing a list of objects whose type is the union of two different dataclasses.

To reproduce

In script.py

from dataclasses import dataclass
from jsonargparse import CLI

@dataclass
class A:
    a: int

@dataclass
class B:
    b: int

def f(c: list[A | B]):
    print(c)

CLI(f, as_positional=False)

In config.yaml

c:
  - a: 1
  - b: 2

In terminal

python script.py --config config.yaml

Expected behavior

Expected console output

[A(a=1), B(b=2)]

Actual console output

ValueError: Does not validate against any of the Union subtypes
Subtypes: (<class '__main__.A'>, <class '__main__.B'>)
Errors:
  - 'LazyInstance_B' object has no attribute 'b'
  - B.__init__() got an unexpected keyword argument 'a'
Given value type: <class 'jsonargparse._namespace.Namespace'>
Given value: Namespace(a=1)

Environment

• jsonargparse version: 4.29.0
• Python version: 3.11.4
• How jsonargparse was installed: pip install jsonargparse[signatures]
• OS: Windows 11 Enterprise, 10.0.22631

[mauvilsa]

Thank you for reporting! I will look at it.

[nkrishnaswami]

I think I'm encountering this or a similar bug when I try to parse a union of attrs classes. The attached testcase
fails when I try to use the second type in a union, with the following output:

E argparse.ArgumentError: Validation failed: Parser key "data":
E Does not validate against any of the Union subtypes
E Subtypes: (<class 'jsonargparse_tests.test_dataclass_like.AttrsData'>, <class 'jsonargparse_tests.test_dataclass_like.AttrsData2'>)
E Errors:
E - No action for key "p4" to set its default.
E - No action for key "p1" to set its default.
E Given value type: <class 'jsonargparse._namespace.Namespace'>
E Given value: Namespace(p1=None, p2='-', p4=1)

jsonargparse/_core.py:1010: ArgumentError

[mauvilsa]

@mnidza just now I reran the reproduction script and it works as expected, giving [A(a=1), B(b=2)]. I am not sure in which change this was fixed. @nkrishnaswami also the TestAttrs::test_union test passes now. Please check and if you like, create a pull request to add your test case.