[GP-02] Forbid sum_connections in objective functions

[Juliette-Gerbaux]

Affected Component

Expression parsing / grammar (expression/, grammar/)

Type of Change

Minor: bug fix or backward-compatible new feature (e.g. new operator)

Description

Forbid sum_connections in objective functions as it is done in Antares_Simulator. This will help Benders decomposition as all objective functions will be local to components.

Results Impact

Forbid sum_connections in objective functions

Validation Strategy

Forbid sum_connections in objective functions

Process Checklist

Step 1 — Issue Creation

• Issue created and linked to process GP-02

Step 2 — Triage

• Process confirmed applicable
• Assigned to responsible contributor
• Priority and milestone set (if applicable)

Step 3 — Impact Analysis ⚠️ extended results analysis required

• Affected modules identified
• Results impact explicitly stated: change intended / no change intended
• If results expected to change: before/after difference described and justified
• Breaking vs backward-compatible change determined

Step 4 — Implementation

• Code changes implemented
• Backward compatibility maintained unless explicitly intended as breaking

Step 5 — Testing & Validation

• If results expected to change: reference studies updated with new expected values
• If results must not change: solver equivalence confirmed via tests
• Unit tests cover changed components

Step 6 — CI Validation

• Type checking passes (mypy)
• Formatting passes (black, isort)
• All tests pass in CI (pytest)

Step 7 — Review & Merge

• PR reviewed; documentation changes included

Step 8 — Versioning

• pyproject.toml version bumped

Step 9 — Supporting Files

• AGENTS.md reviewed for impact and updated if needed

Step 10 — Release

• If a release is needed: follow the release process in the Developer Guidelines