[BugFix] Add variant to non reserved keywords (backport #72356) (#72357)

Signed-off-by: kyle-goodale-klaviyo <kyle.goodale@klaviyo.com>
Co-authored-by: kyle-goodale-klaviyo <kyle.goodale@klaviyo.com>

Author: mergify[bot]

fe/fe-core/src/test/java/com/starrocks/sql/parser/ParserTest.java

@@ -190,6 +190,27 @@ void testNonReservedWords_2() {
         }
     }
 
+    @Test
+    void testVariantAsIdentifier() {
+        // VARIANT was added as a baseType keyword; it must remain usable as an identifier
+        // (bare and backticked) — e.g. as a column name or struct field name.
+        SessionVariable sessionVariable = new SessionVariable();
+        List<String> sqls = Lists.newArrayList(
+                "select variant from t",
+                "select `variant` from t",
+                "select t.variant from t",
+                "select t.`variant` from t",
+                "select cast(c as struct<variant int, other varchar(10)>) from t",
+                "select cast(c as struct<`variant` int, other varchar(10)>) from t");
+        for (String sql : sqls) {
+            try {
+                SqlParser.parse(sql, sessionVariable).get(0);
+            } catch (Exception e) {
+                fail("sql should succeed: " + sql + " errMsg: " + e.getMessage());
+            }
+        }
+    }
+
     @Test
     void testParseLargeDecimal() {
         String sql = "select cast(1 as decimal(85,0))";

fe/fe-grammar/src/main/antlr/com/starrocks/grammar/StarRocks.g4

@@ -3292,7 +3292,7 @@ nonReserved
     | TRIM_SPACE
     | TRIGGERS | TRUNCATE | TYPE | TYPES
     | UNBOUNDED | UNCOMMITTED | UNSET | UNINSTALL | USAGE | USER | USERS | UNLOCK
-    | VALUE | VARBINARY | VARIABLES | VIEW | VIEWS | VERBOSE | VERSION | VOLUME | VOLUMES
+    | VALUE | VARBINARY | VARIABLES | VARIANT | VIEW | VIEWS | VERBOSE | VERSION | VOLUME | VOLUMES
     | WARNINGS | WEEK | WHITELIST | WORK | WRITE  | WAREHOUSE | WAREHOUSES
     | YEAR
     | DOTDOTDOT | NGRAMBF | VECTOR