Support BigQuery array subscript OFFSET(n)

BigQuery addresses array elements positionally with OFFSET(n),
ORDINAL(n), SAFE_OFFSET(n) and SAFE_ORDINAL(n). The latter three already
parsed as functions; OFFSET is a reserved keyword and needed an explicit
array-index rule. The accessor is kept in the AST as a Function so it
deparses unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EqinwHBKuAtPEmtXr3b5P2

Author: hayssams

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

@@ -9459,7 +9459,7 @@ Expression ArrayExpression(Expression obj): {
     Expression stopExpr = null;
 } {
     "["
-        [LOOKAHEAD(3) idxExpr = SimpleExpression()]
+        [LOOKAHEAD(3) idxExpr = ArrayIndexExpression()]
         [
           (":" { startExpr=idxExpr; idxExpr=null; })
           [stopExpr = SimpleExpression()]
@@ -9468,7 +9468,7 @@ Expression ArrayExpression(Expression obj): {
     { expr =  new ArrayExpression(obj, idxExpr, startExpr, stopExpr); }
     (
         LOOKAHEAD(2) "["
-            [LOOKAHEAD(3) idxExpr = SimpleExpression()]
+            [LOOKAHEAD(3) idxExpr = ArrayIndexExpression()]
             [
               (":" { startExpr=idxExpr; idxExpr=null; })
               [stopExpr = SimpleExpression()]
@@ -9479,6 +9479,29 @@ Expression ArrayExpression(Expression obj): {
     { return expr; }
 }
 
+/**
+ * Array subscript index.  BigQuery addresses array elements positionally with
+ * OFFSET(n), ORDINAL(n), SAFE_OFFSET(n) and SAFE_ORDINAL(n).  Only OFFSET needs
+ * an explicit rule here, the others are plain identifiers and parse as functions.
+ */
+Expression ArrayIndexExpression() :
+{
+    Token token;
+    Expression expr;
+}
+{
+    (
+        LOOKAHEAD(2) token = <K_OFFSET> "(" expr = SimpleExpression() ")"
+        {
+            return new Function()
+                    .withName(token.image)
+                    .withParameters(new ExpressionList<Expression>(expr));
+        }
+        |
+        expr = SimpleExpression() { return expr; }
+    )
+}
+
 Expression NavigationStep(Expression base):
 {
     Expression step = null;

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

@@ -10,6 +10,7 @@
 package net.sf.jsqlparser.statement.select;
 
 import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.expression.ArrayExpression;
 import net.sf.jsqlparser.test.TestUtils;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Disabled;
@@ -110,4 +111,26 @@ void testTimeSeriesFunction() throws JSQLParserException {
         TableFunction function = select.getFromItem(TableFunction.class);
         Assertions.assertEquals("TABLE", function.getFunction().getExtraKeyword());
     }
+
+    @Test
+    void testArrayOffsetAccessor() throws JSQLParserException {
+        String sqlStr = "SELECT arr[OFFSET(0)] FROM t";
+        PlainSelect select = (PlainSelect) TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+        ArrayExpression arrayExpression =
+                (ArrayExpression) select.getSelectItem(0).getExpression();
+
+        Assertions.assertEquals("OFFSET(0)", arrayExpression.getIndexExpression().toString());
+    }
+
+    @Test
+    void testArraySafeOffsetAndOrdinalAccessors() throws JSQLParserException {
+        String sqlStr = "SELECT arr[ORDINAL(1)], arr[SAFE_OFFSET(2)], arr[SAFE_ORDINAL(3)] FROM t";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+    }
+
+    @Test
+    void testOffsetClauseStillParses() throws JSQLParserException {
+        String sqlStr = "SELECT a FROM t LIMIT 10 OFFSET 5";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+    }
 }