In new fashion, rule chef must be gay (8)
I believe the answer is:
Here is my best explanation:
'gay' is the definition.
('cheerful' can be a synonym of 'gay')
'in new fashion rule chef' is the wordplay.
'in new fashion' indicates anagramming the letters (I've seen this in other clues).
'rulechef' anagrammed gives 'CHEERFUL'.
'must be' is the link.