Fix LexicaseSelection IndexError on empty candidate pools - #411
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When the evaluator drops invalid individuals or a case filter yields no survivors (e.g. all-NaN fitness), refill from the original population with invalid fitness and keep the pre-filter set so selection can continue. Co-authored-by: Cursor <cursoragent@cursor.com>
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Summary
LexicaseSelection(and weighted/priority variants) against empty candidate pools that previously crashed withIndexErrorat winner selection.problem.get_invalid_fitness().target_size, and NaN case filters.Seen in Aeon CBGP runs with aggressive UMAD mutation: many offspring raise
InvalidFitnessException,SequentialEvaluatordrops them, and lexicase then tries to select ~90% of the population without replacement from a much smaller valid pool.Test plan
pytest tests/gp/lexicase_empty_candidates_test.py tests/gp/unknown_objectives_test.py