Vim highlight a set of words in different colors each in all files

Question

I need vim/Gvim to highlight a set of keywords each with mentioned color in all files (it may be a text file, c source file, or anything else). For example TODO, FIXME are highlighted in C files. Like that, I want to highlight TODO and FIXME in all files each with different colors specified somewhere. This should happen as I open a vim file and do not require me to give a command for this to happen.

How can I achieve this?

Thanks in advance for the help.

Answer 1

Note this is not my answer. Points go to user Ralf, answer copied over from this stackexchange, adding it here for convenience. This is the best solution I could test (if what you want is add custom highlighted words for ALL syntaxes)

function! UpdateTodoKeywords(...)
    let newKeywords = join(a:000, " ")
    let synTodo = map(filter(split(execute("syntax list"), '\n') , { i,v -> match(v, '^\w*Todo\>') == 0}), {i,v -> substitute(v, ' .*$', '', '')})
    for synGrp in synTodo
        execute "syntax keyword " . synGrp . " contained " . newKeywords
    endfor
endfunction

augroup now
    autocmd!
    autocmd Syntax * call UpdateTodoKeywords("NOTE", "NOTES")
augroup END