Issue using with_param and Pydantic IO

[alicederyn]

Pre-bug-report checklist

1. This bug can be reproduced using pure Argo YAML

• Yes 👉 Please report a bug to the Argo Workflows GitHub 👈
• No

If yes, it is more likely to be an Argo bug unrelated to Hera. Please double check before submitting an issue to Hera.

2. I have searched for existing issues

• Yes

3. This bug occurs in Hera when...

• exporting to YAML
• submitting to Argo
• running on Argo with the Hera runner
• other:

Bug report

Describe the bug
When using with_param with a function using Pydantic IO, an extra argument is added with a name matching the incidental argument name used by the script-decorated function, not the parameters from the Pydantic Input type.

To Reproduce
Full Hera code to reproduce the bug:

from hera.workflows import Workflow, Input, Output, script, Steps
from hera.shared import global_config

global_config.experimental_features["script_pydantic_io"] = True

class ListOutput(Output):
    values: list[str]

class PrintInput(Input):
    value: str

@script()
def produce_list() -> ListOutput:
    return ListOutput(values=["item1", "item2"])

@script()
def print_value(input: PrintInput) -> None:
    print("Value:", input.value)


with Workflow(name="my-workflow") as w:
    with Steps(name="steps"):
        list_step = produce_list(arguments={})
        print_value(with_param=list_step.get_parameter("values"))

Expected behavior

- arguments:
    parameters:
    - name: value  # This is actually "input"
      value: '{{item}}'

Environment

• Hera Version: 5.17.1
• Python Version: 3.11.8
• Argo Version: N/A

Additional context
This is the same root cause as #861, i.e. the code in _get_params_items_from_source, but can't be worked around by avoiding using alternative names.

hera/src/hera/workflows/_meta_mixins.py

Lines 266 to 288 in a08f744

	def _get_param_items_from_source(source: Callable) -> List[Parameter]:
	"""Returns a list (possibly empty) of `Parameter` from the specified `source`.
	This infers that each non-keyword, positional, argument of the given source is a parameter that stems from a
	fanout. Therefore, each parameter value takes the form of `{{item}}` when there's a single argument or
	`{{item.<argument name>}}` when there are other arguments.
	Returns:
	-------
	List[Parameter]
	A list of identified parameters (possibly empty).
	"""
	source_signature: List[str] = []
	for p in inspect.signature(source).parameters.values():
	if p.default == inspect.Parameter.empty and p.kind == inspect.Parameter.POSITIONAL_OR_KEYWORD:
	# only add positional or keyword arguments that are not set to a default value
	# as the default value ones are captured by the automatically generated `Parameter` fields for positional
	# kwargs. Otherwise, we assume that the user sets the value of the parameter via the `with_param` field
	source_signature.append(p.name)
	if len(source_signature) == 1:
	return [Parameter(name=n, value="{{item}}") for n in source_signature]
	return [Parameter(name=n, value=f"{{{{item.{n}}}}}") for n in source_signature]