which template determines guest for showthread?

[testbot]

can someone help me find where the code decides if a member is a guest or not when it shows the thread?

for some reason i can't find where it decides to show the "you do not have permission to view this" or the actual thread content.

i'm sure i've just been staring at it for too long and it's prolly right in front of me somewhere really simple.

thanks!