In older versions of Android, the package installer used to show all permissions an app requested – and so did "Android Market" and later also "Google Play Store". A few years ago, the latter started to only show selected permissions, or rather permission groups ("uses one of those permissions" – without saying which). Now it seems with Marshmallow the package installer followed on that insane road, only showing permission groups.
I don't want a "guess", I want facts. When I install an app, I want to see what permissions it requests – exactly. Especially when I apply an update, I not only want to be informed about additional groups requested from, but exactly what permissions have been added – even if some other permission of the same group has already been granted before.
TL;DR: How to make the package installer show all permissions an app-to-be-installed requests?
Rooted approaches acceptable, also if requiring Magisk or Xposed. If doable without any of those, all the better.