Fix: parse struct(...)[] type properly (#4123)

sqlglot/parser.py

@@ -4796,7 +4796,11 @@ def _parse_types(
 
             if self._match_set((TokenType.L_BRACKET, TokenType.L_PAREN)):
                 values = self._parse_csv(self._parse_assignment)
-                self._match_set((TokenType.R_BRACKET, TokenType.R_PAREN))
+                if not values and is_struct:
+                    values = None
+                    self._retreat(self._index - 1)
+                else:
+                    self._match_set((TokenType.R_BRACKET, TokenType.R_PAREN))
 
         if type_token in self.TIMESTAMPS:
             if self._match_text_seq("WITH", "TIME", "ZONE"):

tests/dialects/test_duckdb.py

@@ -18,6 +18,16 @@ def test_duckdb(self):
             "WITH _data AS (SELECT [STRUCT(1 AS a, 2 AS b), STRUCT(2 AS a, 3 AS b)] AS col) SELECT col.b FROM _data, UNNEST(_data.col) AS col WHERE col.a = 1",
         )
 
+        struct_array_type = exp.maybe_parse(
+            "STRUCT(k TEXT, v STRUCT(v_str TEXT, v_int INT, v_int_arr INT[]))[]",
+            into=exp.DataType,
+            dialect="duckdb",
+        )
+        self.assertEqual(
+            struct_array_type.sql("duckdb"),
+            "STRUCT(k TEXT, v STRUCT(v_str TEXT, v_int INT, v_int_arr INT[]))[]",
+        )
+
         self.validate_all(
             "CAST(x AS UUID)",
             write={