[Swift] invalid swift generated for Dynamically-Scoped Attributes

[EXC-BAD-ACCESS]

when using the (slightly altered for swift) grammar from the doc

grammar DynScope;
 
prog: block ;
 
block
    /* List of symbols defined within this block */
    locals [
    symbols: [String]
    ]
    : '{' decl* stat+ '}'
    // print out all symbols found in block
    // $block::symbols evaluates to a List as defined in scope
    {print("symbols=\($symbols)");}
    ;
 
/** Match a declaration and add identifier name to list of symbols */
decl: 'int' ID {$block::symbols.append($ID.text);} ';' ;
 
/** Match an assignment then test list of symbols to verify
 * that it contains the variable on the left side of the assignment.
 * Method contains() is List.contains() because $block::symbols
 * is a List.
 */
stat: ID '=' INT ';'
    {
    if ( !$block::symbols.contains($ID.text) ) {
    print("undefined variable: "+$ID.text);
    }
    }
    | block
    ;
 
ID : [a-z]+ ;
INT : [0-9]+ ;
WS : [ \t\r\n]+ -> skip ;

the generated code is:
(BlockContext)getInvokingContext(1)).symbols.append((_localctx.castdown(DeclContext.self)._ID != nil ? _localctx.castdown(DeclContext.self)._ID!.getText()! : ""));
which uses an invalid c-style cast.

it should generate something like:
(getInvokingContext(1) as! BlockContext).symbols.append((_localctx.castdown(DeclContext.self)._ID != nil ? _localctx.castdown(DeclContext.self)._ID!.getText()! : ""));