How to get the buffer number of `:bn`?

Question

As title. When running :bn the current buffer will be switched to the next buffer. I want to get the buffer number of this buffer without changing the current buffer(or, at least, can switch back to the starting buffer)

Answer 1

I can't fint a build-in solution for this, here is a function using getbufinfo() that does not need to actually change buffers:

function! Next_buf()
    let l:bufs = getbufinfo({'buflisted': 1}

    let l:later = filter(l:bufs), 'v:val.bufnr > ' . bufnr())

    if len(l:later) > 0
        return l:later[0].bufnr
    else
        return l:bufs[0].bufnr
    endif
endfunction

I emulated the behavior of :bn of wrapping around at the end and filtering out hidden buffers.

Answer 2

It turns out that the naive way works: (answer in Lua)

vim.cmd('bn')
local buf_right = vim.fn.bufnr()
vim.cmd('bp')