Fix date serialization

Author: grischard

scripts/generate_dashboard.py

@@ -139,6 +139,7 @@ def run(self: Dashboard) -> None:
                 metric, start_t = futs[fut]
                 try:
                     rows, headers = fut.result()
+                    rows = self._convert_rows(rows)
                 except Exception as exc:  # pragma: no cover - passthrough
                     raise RuntimeError(f"error in metric '{metric.slug}': {exc}") from exc
                 logging.info(
@@ -195,17 +196,25 @@ def _fetch_rows(self: Dashboard, sql: str) -> tuple[list[tuple], list[str]]:
                 cur.execute(sql)
                 rows = cur.fetchall()
                 headers = [d[0] for d in cur.description]
-                # Convert Decimal values to plain Python types for JSON serialisation
-                converted: list[tuple] = []
-                for row in rows:
-                    converted.append(
-                        tuple(float(val) if isinstance(val, Decimal) else val for val in row)
-                    )
-                rows = converted
         finally:
             self.pool.putconn(conn)
         return rows, headers
 
+    def _convert_rows(self: Dashboard, rows: list[tuple]) -> list[tuple]:
+        """Convert non-JSON serialisable types to basic Python types."""
+        converted: list[tuple] = []
+        for row in rows:
+            new_row = []
+            for val in row:
+                if isinstance(val, Decimal):
+                    new_row.append(float(val))
+                elif isinstance(val, (dt.date, dt.datetime)):
+                    new_row.append(val.isoformat())
+                else:
+                    new_row.append(val)
+            converted.append(tuple(new_row))
+        return converted
+
     def _update_history(self: Dashboard, slug: str, value: int) -> None:
         path = self.history_dir / f"{slug}.csv"
         is_new = not path.exists()

tests/test_dashboard.py

@@ -123,6 +123,24 @@ def test_run_handles_decimal_results(tmp_path):
     assert os.path.exists(index)
 
 
+def test_run_handles_date_results(tmp_path):
+    cfg = make_config(tmp_path)
+    metric_dir = cfg["paths"]["metrics_dir"]
+    with open(os.path.join(metric_dir, "date.sql"), "w", encoding="utf-8") as fh:
+        fh.write("-- Title: D\n-- Description: d\nselect CURRENT_DATE as col;\n")
+    dash = make_dashboard(cfg)
+    from datetime import date
+
+    with patch.object(
+        dash,
+        "_fetch_rows",
+        return_value=([(date.today(), 1)], ["col", "num"]),
+    ):
+        dash.run()
+    index = os.path.join(cfg["paths"]["output_dir"], "index.html")
+    assert os.path.exists(index)
+
+
 def test_metrics_sorted_zero_last(tmp_path):
     cfg = make_config(tmp_path)
     metric_dir = cfg["paths"]["metrics_dir"]