fix: ensure start if using end (#2347)

Author: eakmanrq

sqlmesh/core/node.py

@@ -258,7 +258,11 @@ def _node_root_validator(cls, values: t.Dict[str, t.Any]) -> t.Dict[str, t.Any]:
                 raise ConfigError(
                     f"Interval unit of '{interval_unit}' is larger than cron period of '{cron}'"
                 )
-        validate_date_range(values.get("start"), values.get("end"))
+        start = values.get("start")
+        end = values.get("end")
+        if end is not None and start is None:
+            raise ConfigError("Must define a start date if an end date is defined.")
+        validate_date_range(start, end)
         return values
 
     @property

tests/core/test_model.py

@@ -3357,3 +3357,22 @@ def test_end_date():
             """
             )
         )
+
+
+def test_end_no_start():
+    expressions = d.parse(
+        f"""
+        MODEL (
+            name db.table,
+            kind INCREMENTAL_BY_TIME_RANGE (
+                time_column ts,
+            ),
+            end '2023-06-01'
+        );
+
+        SELECT 1::int AS a, 2::int AS b, now::timestamp as ts
+        """
+    )
+    with pytest.raises(ConfigError, match="Must define a start date if an end date is defined"):
+        load_sql_based_model(expressions)
+    load_sql_based_model(expressions, defaults={"start": "2023-01-01"})