Spotlight completely broken

My spotlight index is completely broken. It can't find anything at all, every single thing I search for just returns 'no results'. Here's what I've tried:

• Re-indexing spotlight through System Preferences. I added the Applications folder to the Privacy filter and then deleted it, but it didn't seem to help. Same with other folders that I tried.
• Fixing disk permissions. Permissions weren't broken, so there was nothing to fix.
• Re-installing Sierra. I was ready to lose all my data, I've got it backed up, but it kept all the data I had when I re-installed the OS. And spotlight is still broken.

I'm really confused, not sure where to go from here.

Solution 1:

For anyone who needs the solution, run

sudo mdutil -i off /
sudo mdutil -i on /

This forces a reindex.