model_copy(deep=True) follows __rune_parent links, producing an attached copy instead of a detached subtree.

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@whawk46 arbeitet bereits daran.

Seit 30.10.2026.

  • #54 von @whawk46 — offen

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python
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backend

Rechercherichtung

Start with rune/runtime/cow.py and the BaseDataClass definition, then inspect how model_copy(deep=True) handles dict and PARENT_PROP. Run the included regression test for _clone_for_write and check whether a deep copy omits the parent link while preserving the copied subtree. Done means the clone has no rune parent and deep nested graphs avoid copying their ancestors.

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Beschreibung

Bug Report

Steps to Reproduce:
  1. Build a parent–child object graph (any nested CDM types where fields are
    set via normal assignment, which calls _set_rune_parent).
  2. Call a generated Rune function that writes to a nested field — the function
    body calls _clone_for_write, which calls value.model_copy(deep=True).
  3. For a graph of depth d, observe O(d²) object allocations; for deep CDM
    graphs, observe RecursionError.
Expected Result:

_clone_for_write returns a detached copy with no __rune_parent (the clone is
independent of the original tree).

Actual Result:

model_copy(deep=True) uses copy.deepcopy on dict, which follows the
PARENT_PROP (__rune_parent) pointer up the tree. The clone retains the
original parent reference, and copies of the entire ancestor chain are made.

Environment:

rune-python-runtime 2.2.2, pydantic 2.14.1, Python 3.11

Additional Context:

cow.py _clone_for_write has no special handling for the back-link.
Fix: add a deepcopy override to BaseDataClass that excludes PARENT_PROP
so model_copy(deep=True) produces a detached subtree.

import pytest

import finos._bundle
from finos.cdm.base.staticdata.asset.common.Security import Security
from rune.runtime.cow import _clone_for_write

def test_r3_clone_for_write_copies_rune_parent():
    '''_clone_for_write(child) should produce a detached copy with no
    rune_parent.  Currently model_copy(deep=True) copies the parent link,
    so the clone remains attached to the original parent.'''
    parent = Security.model_construct()
    child = Security.model_construct()
    child._set_rune_parent(parent)

    assert child.get_rune_parent() is parent  # confirm setup

    clone = _clone_for_write(child)

    # A detached clone must not carry the original parent reference.
    # Bug: clone.get_rune_parent() returns the original parent object.
    assert clone.get_rune_parent() is None, (
        '_clone_for_write should produce a detached copy (no rune_parent); '
        f'got {clone.get_rune_parent()}'
    )
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  4. Öffnen Sie einen Pull Request, der die Issue-Nummer nennt.

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