Dart2 grammar fails to parse nested string literals

[levelrin]

I'm using Dart2Parser.g4, Dart2Lexer.g4, and Dart2LexerBase.java.

The grammar could not parse the following code:

void main() {
  String param = '';
  String text = '''
  ${param.isEmpty? '''one
  ''':'''$param'''}two
  ''';
  print(text);
}

Here is the error message:

line 4:22 no viable alternative at input 'voidmain(){Stringparam='';Stringtext='''\n  ${param.isEmpty? '''one'

Here is the Java code to reproduce the issue:

package com.levelrin;

import com.levelrin.antlr.generated.Dart2Lexer;
import com.levelrin.antlr.generated.Dart2Parser;
import com.levelrin.antlr.generated.Dart2ParserBaseListener;
import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.CharStreams;
import org.antlr.v4.runtime.CommonTokenStream;
import org.antlr.v4.runtime.tree.ParseTree;
import org.antlr.v4.runtime.tree.ParseTreeWalker;

public final class Main {

    public static void main(final String... args) {
        final String source = """
            void main() {
              String param = '';
              String text = '''
              ${param.isEmpty? '''one
              ''':'''$param'''}two
              ''';
              print(text);
            }
            """;
        final CharStream charStream = CharStreams.fromString(source);
        final Dart2Lexer lexer = new Dart2Lexer(charStream);
        final CommonTokenStream tokens = new CommonTokenStream(lexer);
        final Dart2Parser parser = new Dart2Parser(tokens);
        final ParseTree tree = parser.compilationUnit();
        final Dart2ParserBaseListener listener = new Dart2ParserBaseListener();
        ParseTreeWalker.DEFAULT.walk(listener, tree);
    }

}