Allow projectile-find-file to search in parent project

[aburlot]

My C++ program is split in two parts, ProjectA and ProjectB. ProjectA is the main framework, has all the base classes. ProjectB inherits from ProjectA and add some physics by specializing the C++ classes. Eglot can easily find references in ProjectA when I am in ProjectB thanks to compile_commands.json, but I cannot use projectile-find-file to search also in ProjectA/src. I cannot figure out a way to tell projectile that it must search somewhere else too, or that ProjectB is linked to ProjectA. I want to create a .dir-locals.el to specify it once and for all in ProjectB. Am I missing something? I can do it with eclipse, but I want to get rid of it thanks to projectile!