Well, I see two possible concerns.

(1) If the tutorial, documentation or some tool uses this option, then this would break the command line API presented by kompile.

(2) Most program use "-" instead of "_" in their command line options.  One reason for this is that "-" is easier to type and is a single keystroke instead of a shift-keystroke (at least on a US Qwerty keyboard).  But, without getting into debates about the aesthetics one versus the other, "-" is much more common and will be more familiar to users.

In the grand scheme of things, both of these concerns are relatively minor, so it comes down to a question of how much we allow the limitations of JCommander to dictate the command line interface.  If it is relatively easy to get JCommander to support "-", then I'd do that, but I understand if it takes a disproportionate amount of code.

(Would it be possible to tell JCommander to convert "-" to "_" and lower case to upper case before trying to match these enums?  That would solve both this issue and the "lower case constant" problem.)