fix: add syntax guard for evolved strategy generation (#321)

src/evolution/optimizer.py

@@ -9,6 +9,7 @@ This module:
 
 from __future__ import annotations
 
+import ast
 import json
 import logging
 import sqlite3
@@ -28,24 +29,24 @@ from src.logging.decision_logger import DecisionLogger
 logger = logging.getLogger(__name__)
 
 STRATEGIES_DIR = Path("src/strategies")
-STRATEGY_TEMPLATE = textwrap.dedent("""\
-    \"\"\"Auto-generated strategy: {name}
+STRATEGY_TEMPLATE = """\
+\"\"\"Auto-generated strategy: {name}
 
-    Generated at: {timestamp}
-    Rationale: {rationale}
-    \"\"\"
+Generated at: {timestamp}
+Rationale: {rationale}
+\"\"\"
 
-    from __future__ import annotations
-    from typing import Any
-    from src.strategies.base import BaseStrategy
+from __future__ import annotations
+from typing import Any
+from src.strategies.base import BaseStrategy
 
 
-    class {class_name}(BaseStrategy):
-        \"\"\"Strategy: {name}\"\"\"
+class {class_name}(BaseStrategy):
+    \"\"\"Strategy: {name}\"\"\"
 
-        def evaluate(self, market_data: dict[str, Any]) -> dict[str, Any]:
-            {body}
-""")
+    def evaluate(self, market_data: dict[str, Any]) -> dict[str, Any]:
+{body}
+"""
 
 
 class EvolutionOptimizer:
@@ -235,7 +236,8 @@ class EvolutionOptimizer:
         file_path = STRATEGIES_DIR / file_name
 
         # Indent the body for the class method
-        indented_body = textwrap.indent(body, "            ")
+        normalized_body = textwrap.dedent(body).strip()
+        indented_body = textwrap.indent(normalized_body, "            ")
 
         # Generate rationale from patterns
         rationale = f"Auto-evolved from {len(failures)} failures. "
@@ -247,9 +249,16 @@ class EvolutionOptimizer:
             timestamp=datetime.now(UTC).isoformat(),
             rationale=rationale,
             class_name=class_name,
-            body=indented_body.strip(),
+            body=indented_body.rstrip(),
         )
 
+        try:
+            parsed = ast.parse(content, filename=str(file_path))
+            compile(parsed, filename=str(file_path), mode="exec")
+        except SyntaxError as exc:
+            logger.warning("Generated strategy failed syntax validation: %s", exc)
+            return None
+
         file_path.write_text(content)
         logger.info("Generated strategy file: %s", file_path)
         return file_path

tests/test_evolution.py

@@ -245,6 +245,52 @@ async def test_generate_strategy_creates_file(optimizer: EvolutionOptimizer, tmp
     assert "def evaluate" in strategy_path.read_text()
 
 
+@pytest.mark.asyncio
+async def test_generate_strategy_saves_valid_python_code(
+    optimizer: EvolutionOptimizer, tmp_path: Path,
+) -> None:
+    """Test that syntactically valid generated code is saved."""
+    failures = [{"decision_id": "1", "timestamp": "2024-01-15T09:30:00+00:00"}]
+
+    mock_response = Mock()
+    mock_response.text = (
+        'price = market_data.get("current_price", 0)\n'
+        'if price > 0:\n'
+        '    return {"action": "BUY", "confidence": 80, "rationale": "Positive price"}\n'
+        'return {"action": "HOLD", "confidence": 50, "rationale": "No signal"}\n'
+    )
+
+    with patch.object(optimizer._client.aio.models, "generate_content", new=AsyncMock(return_value=mock_response)):
+        with patch("src.evolution.optimizer.STRATEGIES_DIR", tmp_path):
+            strategy_path = await optimizer.generate_strategy(failures)
+
+    assert strategy_path is not None
+    assert strategy_path.exists()
+
+
+@pytest.mark.asyncio
+async def test_generate_strategy_blocks_invalid_python_code(
+    optimizer: EvolutionOptimizer, tmp_path: Path, caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Test that syntactically invalid generated code is not saved."""
+    failures = [{"decision_id": "1", "timestamp": "2024-01-15T09:30:00+00:00"}]
+
+    mock_response = Mock()
+    mock_response.text = (
+        'if market_data.get("current_price", 0) > 0\n'
+        '    return {"action": "BUY", "confidence": 80, "rationale": "broken"}\n'
+    )
+
+    with patch.object(optimizer._client.aio.models, "generate_content", new=AsyncMock(return_value=mock_response)):
+        with patch("src.evolution.optimizer.STRATEGIES_DIR", tmp_path):
+            with caplog.at_level("WARNING"):
+                strategy_path = await optimizer.generate_strategy(failures)
+
+    assert strategy_path is None
+    assert list(tmp_path.glob("*.py")) == []
+    assert "failed syntax validation" in caplog.text
+
+
 @pytest.mark.asyncio
 async def test_generate_strategy_handles_api_error(optimizer: EvolutionOptimizer) -> None:
     """Test that generate_strategy handles Gemini API errors gracefully."""