Vim_auto_hlsearch.md

Enable hlsearch whenever the cursor is on any part of a match and disable hlsearch otherwise.

Whenever the cursor is moved the current line is checked if it contains a match for the current search. If it does a range is created that can be compared to the cursor's current column. This matching is repeated for the current line until no more matches are found.

function! AutoHL() abort
  let match_count = 1
  let match_positions = []

  while 1
    let [match_start, match_end] = matchstrpos(getline('.'), @/, 0, match_count)[1:2]
    let match_range = range(match_start, match_end)
    if match_range != [-1]
      let match_count += 1
      call extend(match_positions, match_range[1:])
    else
      break
    endif
  endwhile

  if index(match_positions, col('.')) != -1
    execute !v:hlsearch ? 'set hlsearch'   : ''
  else
    execute  v:hlsearch ? 'set nohlsearch' : ''
  endif
endfunction

augroup HighlightSearch
  autocmd!
  autocmd CursorMoved * call AutoHL()
  autocmd InsertEnter * set nohlsearch
augroup END