[iamthemonster]

The conventional wisdom would be to never mention a job search until you have an offer in hand and you are ready to hand in your resignation letter. If you do mention it, you will be perceived as having half a foot out the door and if your job search falls through (as many do) then you have just telegraphed the fact that you're highly disengaged.

But you don't need to actually mention the job search. If you can put your finger on what's wrong with your current role and you have at least a little trust with your line manager, then you can just say "I'm not happy about XYZ in my role, I want to improve it, have you got any ideas?". And be prepared to bring it up several times.

I don't think anyone is expected to tell their employer they are job hunting.