antlr literal string matching: what am I doing wrong? - antlr4

Question

I've been using antlr for 3 days. I can parse expressions, write Listeners, interpret parse trees... it's a dream come true.
But then I tried to match a literal string 'foo%' and I'm failing. I can find plenty of examples that claim to do this. I have tried them all.
So I created a tiny project to match a literal string. I must be doing something silly.
grammar Test;
clause
: stringLiteral EOF
;
fragment ESCAPED_QUOTE : '\\\'';
stringLiteral : '\'' ( ESCAPED_QUOTE | ~('\n'|'\r') ) + '\'';
Simple test:
public class Test {
#org.junit.Test
public void test() {
String input = "'foo%'";
TestLexer lexer = new TestLexer(new ANTLRInputStream(input));
CommonTokenStream tokens = new CommonTokenStream(lexer);
TestParser parser = new TestParser(tokens);
ParseTree clause = parser.clause();
System.out.println(clause.toStringTree(parser));
ParseTreeWalker walker = new ParseTreeWalker();
}
}
The result:
Running com.example.Test
line 1:1 token recognition error at: 'f'
line 1:2 token recognition error at: 'o'
line 1:3 token recognition error at: 'o'
line 1:4 token recognition error at: '%'
line 1:6 no viable alternative at input '<EOF>'
(clause (stringLiteral ' ') <EOF>)
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.128 sec - in com.example.Test
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
The full maven-ized build tree is available for a quick review here
31 lines of code... most of it borrowed from small examples.
$ mvn clean test
Using antlr-4.5.2-1.

Answer 1

fragment rules can only be used by other lexer rules. So, you need to make stringLiteral a lexer rule instead of a parser rule. Just let it start with an upper case letter.
Also, it's better to expand your negated class ~('\n'|'\r') to include a backslash and quote, and you might want to include a backslash to be able to be escaped:
clause
: StringLiteral EOF
;
StringLiteral : '\'' ( Escape | ~('\'' | '\\' | '\n' | '\r') ) + '\'';
fragment Escape : '\\' ( '\'' | '\\' );