call a function with buffer as temporary current buffer This temporarily switches current buffer to "buffer". If the current window already shows "buffer", the window is not switched If a window inside the current tabpage (including a float) already shows the buffer One of these windows will be set as current window temporarily. Otherwise a temporary scratch window (called the "autocmd window" for historical reasons) will be used. This is useful e.g. to call vimL functions that only work with the current buffer/window currently, like |termopen()|. Parameters: ~ {buffer} Buffer handle, or 0 for current buffer {fun} Function to call inside the buffer (currently lua callable only) Return: ~ Return value of function. NB: will deepcopy lua values currently, use upvalues to send lua references in and out.