fix: support nested parametric data types as CAST target

ClickHouse allows parametric (constructor-style) data types as a CAST
target, including nested ones such as Nullable(Decimal(10, 2)). Parsing
failed because the argument production of ColDataType only accepted
atomic tokens (numbers, string literals, bare identifiers/keywords), so
the inner opening bracket of a nested parametric type was unexpected.

Allow an argument that is itself a parametric data type (a DATA_TYPE or
identifier immediately followed by an argument list) to be parsed as a
nested ColDataType, recursing through the existing production. The
nested type is rendered back via its toString() so the statement
round-trips.

Fixes #2441

Signed-off-by: 付典 <fudianchn@gmail.com>

Author: fudianchn

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -10707,6 +10707,7 @@ ColDataType ColDataType():
     List<Integer> array = new ArrayList<Integer>();
     List<String> name;
     ColDataType arrayType;
+    ColDataType nestedType = null;
 
     int precision = -1;
     int scale = -1;
@@ -10755,6 +10756,9 @@ ColDataType ColDataType():
     [
         LOOKAHEAD(2) "(" {tk2 =null;}
         (
+            (
+            LOOKAHEAD((<DATA_TYPE> | <S_IDENTIFIER>) "(") nestedType=ColDataType()
+            |
             (
                 (
                     ( tk=<S_LONG> | tk=<K_MAX> ) [ LOOKAHEAD(2) (tk2=<K_BYTE> | tk2=<K_CHAR>) ]
@@ -10765,9 +10769,15 @@ ColDataType ColDataType():
                 tk=<S_IDENTIFIER>
                 |
                 tk=<K_CHAR>
+            )
             )
 		    {
-		        argumentsStringList.add(tk.image + (tk2!=null?" " + tk2.image:""));
+            if (nestedType != null) {
+                argumentsStringList.add(nestedType.toString());
+                nestedType = null;
+            } else {
+                argumentsStringList.add(tk.image + (tk2!=null?" " + tk2.image:""));
+            }
             }
 
             [ "," ]

src/test/java/net/sf/jsqlparser/statement/select/ClickHouseTest.java

@@ -140,4 +140,16 @@ public void testMultipleSettingsClauseIssue2362() throws JSQLParserException {
         Assertions.assertNotNull(select.getSettings());
         Assertions.assertEquals(2, select.getSettings().size());
     }
+
+    @Test
+    public void testCastToNestedParametricTypeIssue2441() throws JSQLParserException {
+        // ClickHouse allows parametric (constructor-style) data types as a CAST target,
+        // including nested ones such as Nullable(Decimal(p, s)).
+        String sql = "SELECT CAST(x AS Nullable(Decimal(10, 2))) FROM cast_demo";
+        assertSqlCanBeParsedAndDeparsed(sql, true);
+
+        // The inner parametric type may itself be wrapped by another parametric type.
+        sql = "SELECT CAST(x AS LowCardinality(Decimal(10, 2))) FROM cast_demo";
+        assertSqlCanBeParsedAndDeparsed(sql, true);
+    }
 }