My to-do list is a plain text .txt file that I load in Vim. In .txt files Vim has always coloured hash marks (#) and the text following them on the same line, which I use to mark out urgent to-do items. The other day this highlighting disappeared and I can't for the life of me see how to restore it. I've turned on all the syntax and filetype commands I can find. Should I have a text.vim or txt.vim syntax file that I might've deleted without realising? It feels like there should be a simple solution, but I can't find anything approaching a simple solution from googling round - I'm certainly not going to reinstall, write a custom syntax file, use a complex script, etc., I just want the default behaviour back :-)
I don't think that your Vim is broken. Try putting a hash mark (#) at the beginning of the first line in the file. When Vim sees this, it sets the filetype to conf (for a configuration file). As far as I know, Vim does not syntax color vanilla text files.