Fix: attach comments to Commands (#3758)

Author: georgesittas

sqlglot/generator.py

@@ -512,6 +512,7 @@ class Generator(metaclass=_Generator):
 
     # Expressions whose comments are separated from them for better formatting
     WITH_SEPARATED_COMMENTS: t.Tuple[t.Type[exp.Expression], ...] = (
+        exp.Command,
         exp.Create,
         exp.Delete,
         exp.Drop,

sqlglot/parser.py

@@ -1478,7 +1478,10 @@ def _warn_unsupported(self) -> None:
     def _parse_command(self) -> exp.Command:
         self._warn_unsupported()
         return self.expression(
-            exp.Command, this=self._prev.text.upper(), expression=self._parse_string()
+            exp.Command,
+            comments=self._prev_comments,
+            this=self._prev.text.upper(),
+            expression=self._parse_string(),
         )
 
     def _try_parse(self, parse_method: t.Callable[[], T], retreat: bool = False) -> t.Optional[T]:

tests/dialects/test_bigquery.py

@@ -1427,6 +1427,12 @@ def test_errors(self):
             transpile("DATE_ADD(x, day)", read="bigquery")
 
     def test_warnings(self):
+        with self.assertLogs(parser_logger) as cm:
+            self.validate_identity(
+                "/* some comment */ DECLARE foo DATE DEFAULT DATE_SUB(current_date, INTERVAL 2 day)"
+            )
+            self.assertIn("contains unsupported syntax", cm.output[0])
+
         with self.assertLogs(helper_logger) as cm:
             self.validate_identity(
                 "WITH cte(c) AS (SELECT * FROM t) SELECT * FROM cte",