feat: parse BigQuery JSON string literals as implicit casts (#2488)

isImplicitCastAhead() only fired for DATA_TYPE and DT_ZONE tokens, but
JSON lexes as K_JSON, so BigQuery literals like JSON '{"a": 1}' failed
to parse even though DataType() accepts K_JSON as a data type. Accept
K_JSON when directly followed by a string literal.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: hayssams

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

@@ -477,6 +477,8 @@ public class CCJSqlParser extends AbstractJSqlParser<CCJSqlParser> {
             // DT_ZONE (TIMESTAMP WITH TIME ZONE / WITHOUT TIME ZONE) is also a valid
             // implicit cast type prefix handled by DataType(), but distinct from DATA_TYPE.
             if (k1 == DT_ZONE) return true;
+            // BigQuery JSON 'literal' - JSON lexes as K_JSON, but DataType() accepts it
+            if (k1 == K_JSON) return getToken(2).kind == S_CHAR_LITERAL;
             if (k1 != DATA_TYPE) return false;
             int k2 = getToken(2).kind;
             if (k2 != OPENING_BRACKET) return true; // DATA_TYPE literal - simple cast

src/test/java/net/sf/jsqlparser/expression/CastExpressionTest.java

@@ -52,6 +52,18 @@ void testImplicitCast() throws JSQLParserException {
         Assertions.assertTrue(select.getSelectItem(0).getExpression() instanceof CastExpression);
     }
 
+    @Test
+    void testImplicitCastJsonLiteral() throws JSQLParserException {
+        String sqlStr = "SELECT JSON '{\"name\": \"Jakob\"}'";
+        PlainSelect select = (PlainSelect) TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+
+        Assertions.assertTrue(select.getSelectItem(0).getExpression() instanceof CastExpression);
+
+        // BigQuery wraps JSON literals in functions, e. g. BOOL(JSON 'true')
+        sqlStr = "SELECT BOOL(JSON 'true') AS vacancy";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+    }
+
     @Test
     void testImplicitCastTimestampIssue1364() throws JSQLParserException {
         String sqlStr = "SELECT TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'";