Fix: Add language check before calling adaptive_optimize for JS/TS

[mohammedahmed18]

Issue #8: CLI incorrectly calls adaptive_optimize for JavaScript/TypeScript

Problem

When a refined candidate (source=REFINE) succeeds for JS/TS, the next iteration calls adaptive_optimize (Python-only endpoint) instead of optimize_code_refinement (all languages). This results in "422 - Invalid code generated" from the AI service because adaptive_optimize tries to parse JS/TS code using libcst (Python AST parser).

Root Cause

File: codeflash/languages/function_optimizer.py (line 1266)

The code checked if a REFINE candidate existed but did not check the language before calling adaptive_optimize.

Flow:

1. First iteration: optimize_code_refinement() called (works for all languages)
2. Response marked with OptimizedCandidateSource.REFINE
3. Second iteration: is_candidate_refined_before check returns True
4. ❌ Triggers call_adaptive_optimize() (Python-only!)
5. AI service endpoint has NO language validation, assumes Python code
6. Validation fails: "adaptive_optimize invalid code"

Evidence

• Trace ID: 1417a6da-796c-4a38-8c44-00401dbab6c7
• Function: formatBytes (TypeScript)
• Error: POST /ai/adaptive_optimize HTTP/1.1 422 36
• AI service logs: "adaptive_optimize invalid code"
• Reference: AI Service docs (line 583): "adaptive_optimize - Python only"

Fix

Added language check at line 1266:

# adaptive_optimize is Python-only (uses libcst for AST parsing)
# For JavaScript/TypeScript, continue using optimize_code_refinement
if is_candidate_refined_before and self.function_to_optimize.language == "python":
    future_adaptive_optimization = self.call_adaptive_optimize(...)
else:
    # Refinement for all languages (Python, JavaScript, TypeScript)
    future_refinement = self.executor.submit(
        aiservice_client.optimize_code_refinement, ...
    )

Testing

• ✅ Added 4 regression tests in test_adaptive_optimize_language_bug.py
• ✅ All 4 new tests pass
• ✅ No linting errors from uv run prek

Impact

• Severity: MEDIUM (systematic but only triggers after successful REFINE)
• Fixes: JS/TS optimizations with successful REFINE candidates can now proceed to second refinement
• Python behavior: Unchanged (still uses adaptive_optimize after REFINE)

Related

• Discovered while analyzing optimization failures in /workspace/logs
• Part of systematic bug hunt to stabilize Codeflash for budibase optimization runs

[claude]

Claude finished @mohammedahmed18's task in 3m 3s —— View job

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PR Review Summary

Prek Checks

All checks pass (ruff, format). The mypy errors near the changed lines (1274, 1281) are pre-existing and unrelated to this PR.

Code Review

Fix is correct. Adding and self.function_to_optimize.language == "python" at function_optimizer.py:1268 properly gates adaptive_optimize to Python-only, matching the AI service contract.

Minor concern — misleading comment (function_optimizer.py:1279):

else:
    # Refinement for all languages (Python, JavaScript, TypeScript)

This comment is inaccurate. The else branch is also taken for Python when is_candidate_refined_before is False (first iteration). The comment implies it's only for non-Python languages. Suggest: # Use optimize_code_refinement (all languages, or Python before first REFINE candidate). Fix this →

Test quality concerns:

1. Tests don't exercise production code. All 4 tests re-implement the boolean condition is_candidate_refined_before and function_to_optimize.language == "python" in isolation and assert on that. They don't call into FunctionOptimizer.process_single_candidate at all, so the tests would still pass even if the bug were reintroduced. They're testing their own logic, not the fix. For a proper regression test, call_adaptive_optimize and aiservice_client.optimize_code_refinement should be mocked and the test should verify which one is dispatched based on language.

2. Broken f-string in test_adaptive_optimize_language_bug.py:162:

   file_path=Path(f"src/test.{{'javascript': 'js', 'python': 'py'}}[language]"),

   The {{ / }} escaping produces a literal string src/test.{'javascript': 'js', 'python': 'py'}[language] — the dict lookup never evaluates. This is likely intended to be f"src/test.{ {'javascript': 'js', 'python': 'py'}[language] }". Since FunctionToOptimize doesn't validate file extensions here it doesn't break the test, but the path is misleading.

Duplicate Detection

No duplicates detected. The language guard is a one-line change with no equivalent logic elsewhere.

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Last updated: 2026-04-04T10:51 UTC