I have a language that extends Java. I.e. I can compile Java, but have some additional declarations.
So, I want to see those declarations with my compiler, but hide then from javac. For this I use a special not a comment block, like

package foo;
/*{
pragma enable feature;
}*/
include java.util.*;

The idea is that javac will think /*{ … }*/ is a multiline comment, but my lexer just ignores /*{ and }*/ tokens. That’s how it was implemented by JavaCC. Now I need to switch to use JFlex. And I can’t find a way to specify these not a comment tokens.

Let’s say I start with

LINE_COMMENT= "//" .*
BLOCK_COMMENT= "/" * ( [^*] | *+ [^*/] )* ( *+ "/" )?

Then add my special comments

SPECIAL_COMMENT= "/*{" | "}*/"

This does not help, since JFlex always try to find the longest match, and

/*{
pragma enable feature;
}*/

Is matched by BLOCK_COMMENT (it’s longer then SPECIAL_COMMENT).
Ok, I reject { to be the third character, like

LINE_COMMENT= "//" .*
SPECIAL_COMMENT= "/*{" | "}*/"
BLOCK_COMMENT= "/" * [^{] ( [^*] | *+ [^*/] )* ( *+ "/" )?

Now block comment cannot start with /*{ and lexer returns SPECIAL_COMMENT. But for

/**/
/*{
pragma enable feature;
}*/

code my trick does not work, since BLOCK_COMMENT starts with /*, then eats any character except { (the second * character) and starts to look over for the comment end (*/ is not the end, sine * was already consumed).

I spent many hours trying to find a way for this /**/ case, but no luck. Any sugestions?