On a PostgreSQL project, I suddenly got this error when trying to run PostgreSQL:

The data directory was initialized by PostgreSQL version 10, which is not compatible with this version 11.5.

W00t? It turns our that a brew update sometime ago upgraded PostgreSQL to 11.5 and now my data is incompatible.

After a lot of googling, I found that you can install a package that automatically upgrades all your databases to the new version and everything is fine and dandy. Just install:

brew postgresql-upgrade-database

And voila, everything works as before! Thank you internet!