`restore_simulation` silently drops memberless group entities

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
python
Domain
backend

Research direction

Start in policyengine_core/tools/simulation_dumper.py at restore_simulation, then compare the inherited implementation with the reference fix in openfisca/openfisca-core#1387. Done means restored entity counts match the dumped ids, memberless group entities remain present, and simulations without group entities restore without UnboundLocalError.

Written by the indexing model from the issue text.

Description

policyengine_core/tools/simulation_dumper.py (inherited verbatim from openfisca-core) rebuilds entity counts from the members mapping instead of the dumped ids:

person_count = len(population.members_entity_id)
population.count = max(population.members_entity_id) + 1

Consequences, all verified against the equivalent code in openfisca-core:

  1. A group entity with no member is silently dropped from the restored simulation's count, while still listed in its ids — an internally inconsistent state. Calculations on the restored simulation then return arrays with one entity missing, with no error. If a value was stored for the group entity, restoring instead fails with ValueError: length is N while there are N-1 ….
  2. A tax-benefit system with no group entity cannot be restored at all: person_count is never assigned and restore_simulation raises UnboundLocalError.

Upstream report and reference fix (restore each entity's count from its own dumped id.npy, which also removes the person_count plumbing): openfisca/openfisca-core#1387.

Happy to open the twin PR here if useful.

Dominant language
Python
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Forks
30
Avg merge
14h 33m
Merged PRs (30d)
7

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