Fix parsing error when having fields after nested struct in BigQuery

Before applying this patch, the following SQL cannot be parsed:

```SQL
CREATE TABLE my_table (
  f0 STRING,
  f1 STRUCT<a STRING, b STRUCT<c INT64, d STRING>>,
  f2 STRING,
)
```

But it's a valid SQL in BigQuery. The root cause is having comma after
the trailing bracket will be reconigized as a mismatched closing.

Author: git-hulk

src/parser/mod.rs

@@ -3034,7 +3034,6 @@ impl<'a> Parser<'a> {
     where
         F: FnMut(&mut Parser<'a>) -> Result<(StructField, MatchedTrailingBracket), ParserError>,
     {
-        let start_token = self.peek_token();
         self.expect_keyword_is(Keyword::STRUCT)?;
 
         // Nothing to do if we have no type information.
@@ -3047,16 +3046,10 @@ impl<'a> Parser<'a> {
         let trailing_bracket = loop {
             let (def, trailing_bracket) = elem_parser(self)?;
             field_defs.push(def);
-            if !self.consume_token(&Token::Comma) {
+            // The struct field definition is finished if it occurs `>>` or comma.
+            if trailing_bracket.0 || !self.consume_token(&Token::Comma) {
                 break trailing_bracket;
             }
-
-            // Angle brackets are balanced so we only expect the trailing `>>` after
-            // we've matched all field types for the current struct.
-            // e.g. this is invalid syntax `STRUCT<STRUCT<INT>>>, INT>(NULL)`
-            if trailing_bracket.0 {
-                return parser_err!("unmatched > in STRUCT definition", start_token.span.start);
-            }
         };
 
         Ok((

tests/sqlparser_bigquery.rs

@@ -2472,3 +2472,52 @@ fn test_struct_field_options() {
         ")",
     ));
 }
+
+#[test]
+fn test_struct_trailing_bracket() {
+    bigquery().verified_stmt(concat!(
+        "CREATE TABLE my_table (",
+        "f0 STRING, ",
+        "f1 STRUCT<a STRING, b STRUCT<c INT64, d STRING>>, ",
+        "f2 STRING",
+        ")",
+    ));
+
+    // More complex nested structs
+    bigquery().verified_stmt(concat!(
+        "CREATE TABLE my_table (",
+        "f0 STRING, ",
+        "f1 STRUCT<a STRING, b STRUCT<c INT64, d STRUCT<e STRING>>>, ",
+        "f2 STRUCT<h STRING, i STRUCT<j INT64, k STRUCT<l STRUCT<m STRING>>>>, ",
+        "f3 STRUCT<e STRING, f STRUCT<c INT64>>",
+        ")",
+    ));
+
+    // Bad case with missing closing bracket
+    assert_eq!(
+        ParserError::ParserError("Expected: >, found: )".to_owned()),
+        bigquery()
+            .parse_sql_statements("CREATE TABLE my_table(f1 STRUCT<a STRING, b INT64)")
+            .unwrap_err()
+    );
+
+    // Bad case with redundant closing bracket
+    assert_eq!(
+        ParserError::ParserError(
+            "unmatched > after parsing data type STRUCT<a STRING, b INT64>)".to_owned()
+        ),
+        bigquery()
+            .parse_sql_statements("CREATE TABLE my_table(f1 STRUCT<a STRING, b INT64>>)")
+            .unwrap_err()
+    );
+
+    // Base case with redundant closing bracket in nested struct
+    assert_eq!(
+        ParserError::ParserError(
+            "Expected: ',' or ')' after column definition, found: >".to_owned()
+        ),
+        bigquery()
+            .parse_sql_statements("CREATE TABLE my_table(f1 STRUCT<a STRUCT<b INT>>>, c INT64)")
+            .unwrap_err()
+    );
+}