setbufline.vim

function! SetBufLine(expr, lnum, text)
  let oldnr = winnr()
  let winnr = bufwinnr(a:expr)

  try
    if oldnr == winnr
      silent! call setline(a:lnum, a:text)
    elseif winnr ==# -1
      silent split
      silent execute bufnr(a:expr) 'buffer'
      silent call setline(a:lnum, a:text)
      silent hide
    else
      execute winnr 'wincmd w'
      silent call setline(a:lnum, a:text)
    endif
  finally
    execute oldnr 'wincmd w'
  endtry
endfunction