All books and dictionaries (notably Wiktionary) that transcribe french pronunciation by means of IPA transcribe the pronunciation of “u” as /y/. But the transcription uses /.../ as opposed to [...]. When I use [y] in my speech, my teacher corrects me and says [ʏ]. Could it be the case that all these textbooks and dictionaries use /y/ instead /ʏ/ in the open transcriptions, and that this is inaccurate?
TL;DR: Should “u” be pronounced [y] (close front rounded vowel) or [ʏ] (near-close near-front rounded vowel)?
Resolution: I mistook [y̠] (close front compressed vowel) for [ʏ] due to my lacking knowledge of the diacritic. A cognitive bias, if you will.