I am upgrading from 4.2 directly to 5.1 and run into problems with the Html and Form classes.
I followed the upgrade notes, and did
My problem is solved, but the actual cause is still unknown. I have created a completely new laravel install and copied my source (all of it). The new application worked right away (after installing illuminate/html).
So you think I did something wrong with packages? That's what I thought, and then I did a diff on the two directories, only to find out they were identical. So it's a real mystery.
So, now everything is working, I simply renamed my new application and can continue.
I do know at some point I probably had both the collective and the illuminate versions of the HTML package installed. That's what most likely corrupted everything.