This compiler finally sets small problem (4)
I believe the answer is:
Here is my best explanation:
'problem' is the definition.
'this compiler finally sets small' is the subsidiary indication.
'this compiler' becomes 'me' (the person who is writing these clues).
'finally' indicates one should take the final letters.
'small' becomes 's' (abbreviation - e.g. clothes size).
The last letter of 'sets' is 's'.
(Other definitions for mess that I've seen before include "Disagreeable mixture", "sloppy > food", "Military dining room", "Where soldiers may eat", "State of disorder", "Military dining area", "Officers' restaurant - what a dump", "pickle", "State of confusion or untidiness" and "Untidy confusion".)