parser: use ExpressionListOpt for json functions. (#3362)

parser/parser.y

@@ -3642,28 +3642,17 @@ FunctionCallNonKeyword:
 	{
 		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: $3.([]ast.ExprNode)}
 	}
-|	"JSON_EXTRACT" '(' Expression ',' ExpressionList ')'
+|	"JSON_EXTRACT" '(' ExpressionListOpt ')'
 	{
-		var args = []ast.ExprNode{$3.(ast.ExprNode)}
-		args = append(args, $5.([]ast.ExprNode)...)
-		$$ = &ast.FuncCallExpr{
-			FnName: model.NewCIStr($1),
-			Args: args,
-		}
+		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: $3.([]ast.ExprNode)}
 	}
-|	"JSON_UNQUOTE" '(' Expression ')'
+|	"JSON_UNQUOTE" '(' ExpressionListOpt ')'
 	{
-		$$ = &ast.FuncCallExpr{
-			FnName: model.NewCIStr($1),
-			Args: []ast.ExprNode{$3.(ast.ExprNode)},
-		}
+		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: $3.([]ast.ExprNode)}
 	}
-|	"JSON_TYPE" '(' Expression ')'
+|	"JSON_TYPE" '(' ExpressionListOpt ')'
 	{
-		$$ = &ast.FuncCallExpr{
-			FnName: model.NewCIStr($1),
-			Args: []ast.ExprNode{$3.(ast.ExprNode)},
-		}
+		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: $3.([]ast.ExprNode)}
 	}
 
 GetFormatSelector:

parser/parser_test.go

@@ -1026,6 +1026,12 @@ func (s *testParserSuite) TestBuiltin(c *C) {
 		{`SELECT UNCOMPRESS('any string');`, true},
 		{`SELECT UNCOMPRESSED_LENGTH(@compressed_string);`, true},
 		{`SELECT VALIDATE_PASSWORD_STRENGTH(@str);`, true},
+
+		// For JSON functions.
+		{`SELECT JSON_EXTRACT();`, true},
+		{`SELECT JSON_UNQUOTE();`, true},
+		{`SELECT JSON_TYPE('[123]');`, true},
+		{`SELECT JSON_TYPE();`, true},
 	}
 	s.RunTest(c, table)
 }