Snowflake: parse nested COPY transformation paths

src/dialect/snowflake.rs

@@ -1602,10 +1602,14 @@ fn parse_select_item_for_data_load(
         }
     }
 
-    // A trailing `::` means this is a cast expression (e.g.
-    // `$1:"col"::NUMBER(38,0)`), not a stage-load-select-item.
-    if matches!(parser.peek_token_ref().token, Token::DoubleColon) {
-        return parser.expected("stage load select item", parser.peek_token());
+    // More complex paths and casts must fall back to the standard expression
+    // parser so it can preserve the complete JsonAccess / Cast expression.
+    if matches!(
+        parser.peek_token_ref().token,
+        Token::Colon | Token::Period | Token::LBracket | Token::DoubleColon
+    ) {
+        let token = parser.next_token();
+        return parser.expected("end of simple staged field", token);
     }
 
     // as

tests/sqlparser_snowflake.rs

@@ -2596,6 +2596,11 @@ fn test_copy_into_with_cast_transformation() {
             "COPY INTO my_company.emp_basic (a, b) FROM ",
             r#"(SELECT t.$1:plain AS plain, $1:"B"::TEXT FROM @stg AS t)"#,
         ),
+        // https://docs.snowflake.com/en/user-guide/tutorials/script-data-load-transform-parquet
+        concat!(
+            "COPY INTO my_company.emp_basic (a, b) FROM ",
+            "(SELECT $1:continent::VARCHAR, $1:country:name::VARCHAR FROM @stg)",
+        ),
     ];
     for sql in variants {
         snowflake().verified_stmt(sql);