ANTLR4: lexer rule for: Any string as long as it doesn't contain these two side-by-side characters? - antlr

Question

Is there any way to express this in ANTLR4:
Any string as long as it doesn't contain the asterisk immediately
followed by a forward slash?
This doesn't work: (~'*/')* as ANTRL throws this error: multi-character literals are not allowed in lexer sets: '*/'
This works but isn't correct: (~[*/])* as it prohibits a string containing the individual character * or /.

Answer 1

I had similar problem, my solution: ( ~'*' | ( '*'+ ~[/*]) )* '*'*.

Answer 2

The closest I can come is to put the test in the parser instead of the lexer. That's not exactly what you're asking for, but it does work.
The trick is to use a semantic predicate before any string that must be tested for any Evil Characters. The actual testing is done in Java.
grammar myTest;
#header
{
import java.util.*;
}
#parser::members
{
boolean hasEvilCharacters(String input)
{
if (input.contains("*/"))
{
return false;
}
else
{
return true;
}
}
}
// Mimics a very simple sentence, such as:
// I am clean.
// I have evil char*/acters.
myTest
: { hasEvilCharacters(_input.LT(1).getText()) }? String
(Space { hasEvilCharacters(_input.LT(1).getText()) }? String)*
Period EOF
;
String
: ('A'..'Z' | 'a'..'z')+
;
Space
: ' '
;
Period
: '.'
;
Tested with ANTLR 4.4 via the TestRig in ANTLRWorks 2 in NetBeans 8.0.1.

Answer 3

If the disallowed sequences are few there exists a solution without parser/lexer actions:
grammar NotParser;
program
: (starslash | notstarslash)+
;
notstarslash
: NOT_STAR_SLASH
;
starslash
: STAR_SLASH
;
STAR_SLASH
: '*'+ '/'
;
NOT_STAR_SLASH
: (F_NOT_STAR_SLASH | F_STAR_NOT_SLASH) +
;
fragment F_NOT_STAR_SLASH
: ~('*'|'/')
;
fragment F_STAR_NOT_SLASH
: '*'+ ~('*'|'/')
| '*'+ EOF
| '/'
;
The idea is to compose the token of
all tokens that are neither '*' nor '/'
all tokens that begin with '*' but are not followed with '/' or single '/'
There are some rules that deal with special situations (multiple '' followed by '/', or trailing '')