Highlighting after a line limit

Question

I'd like to highlight sections of a document which are too long (measured in lines) so they will all print on a physical page. Sections are separated with ===. I tried to do it with this code:

matchadd('ErrorMsg', '\%(^\|===\n\)\%(.*\n\)\{5}\zs\%(.*\n\)\+\ze', -1)

Everything works hunky-dory. But when I increase the size:

matchadd('ErrorMsg', '\%(^\|===\n\)\%(.*\n\)\{80}\zs\%(.*\n\)\+\ze', -1)

matches don't highlight. From the documentation :matchadd:

Defines a pattern to be highlighted in the current window (a
    "match")

Based on figuring out where exactly the problem happens, I think it's not using text outside the current window. What should I be doing instead? Sections are already associated with folds if that helps.

Answer 1

If you are not insisting on using matchadd you can try to use properties, here is the proof of concept you can play with:

call prop_type_add('TEST', {'highlight': 'ErrorMsg'})

"screen jumps sometimes, try to find your own way
func! UpdatePage(pagesize) abort
    let cpos = getcurpos()
    1
    call prop_clear(1, line('$'))
    while search('^|===$', 'Wc')
        normal! j
        let next_section = search('\(^|===$\)\|\%$', 'Wn')
        let next_section = (next_section == line('$')?line('$'):next_section-1)
        if next_section - line('.') > a:pagesize
            call prop_add(line('.') + a:pagesize, 1, {'end_lnum': next_section, 'end_col': 1000, 'type': 'TEST'})
        endif
    endwhile
    call setpos('.', cpos)
endfunc

" TODO: add it to its own group
au! InsertLeave * call UpdatePage(80)

Answer 2

A much simpler option is to set colorcolumn=80 or whatever number(s) you want: then you have a line down the screen that shows your breakpoint.

Answer 3

How about :au BufWinEnter * let w:m1=matchadd('ErrorMsg', '\(^===\)\_p\{20,}\1', -1) ?

This works with my little lorem ipsum test case.

The solution here is \_p\{20,}, which matches at least 20 printable characters including newline (that is the _).

I tried this with a little "lorem ipsum", consecutive blocks are also highlighted, which makes the whole affair quite colorful...