field_manager behavior change from v11.3.0 to v12.0.0

[dtrai2]

The field_manager processor had a behavior change in the last version that was not highlighted as a breaking change. It should be discussed if this new behavior is wanted or if the old behavior should be recovered.

Changed behavior
In the previous version the field_manager could turn a target_field that already existed, and which was not of type list, into a list by appending a source_field with the argument extend_Target_list: true. In version 12 the field_manager now complains and adds a _field_manager_failure tag instead.

Steps to reproduce
Add the following test case to the tests/unit/processor/field_manager/test_field_manager.py test_cases list and execute it with logprep version 11.3.0 and logprep version 12.0.0. In one version the test passes and in the other version the test fails.

test_cases = [  # testcase, rule, event, expected
    (
        "Convert existing target to list",
        {
            "filter": "message",
            "field_manager": {
                "source_fields": ["message"],
                "target_field": "new_field",
                "extend_target_list": True
            },
        },
        {"message": "Value B", "new_field": "Value A"},
        {"message": "Value B", "new_field": ["Value A", "Value B"]},
)]

@ekneg54 @djkhl what are your takes on it?

[ekneg54]

confirmed ... I think this is a bug. It should be as you suggested