Alba, Bloom, Diddy -- Epic Star-Studded Birthday Bash

Hollywood was oozing with stars last night ... thanks to Heather Parry -- a film and TV producer and Head of Happy Madison Productions -- who threw herself a celeb-filled birthday party at The Nice Guy.

Heather's guest list included Jessica Alba, Orlando Bloom, Nicole Ritchie, Diddy, Toby Maguire, Katharine McPhee ... and of course, Adam Sandler ... to name just a few.

Machine Gun Kelly also made a loud appearance ... but no word on if he was on Heather's roster.