Misunderstanding of interaction between local options, moving between windows, and WinLeave, WinEnter, BufLeave, BufEnter events

Question

This what is logged in :messages when I'm printing the value of nu and rnu upon the 4 events WinLeave, WinEnter, BufLeave, BufEnter during the action, done twice, of opening :help and closing it. The erroenous command fffffff... was the fastest way make a visual separation between the 4 actions (:h, :q, :h, :q).

"relativenumber.vim" 9L, 468B
WinLeave relativenumber.vim (nu = 1, rnu = 1)
WinEnter relativenumber.vim (nu = 1, rnu = 1)
BufLeave relativenumber.vim (nu = 1, rnu = 1)
BufEnter  (nu = 0, rnu = 0)
"help.txt" [readonly] 253L, 9491B
BufEnter /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)
E492: Not an editor command: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
BufLeave /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)
WinLeave /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)
WinEnter relativenumber.vim (nu = 1, rnu = 1)
BufEnter relativenumber.vim (nu = 1, rnu = 1)
E492: Not an editor command: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
WinLeave relativenumber.vim (nu = 1, rnu = 1)
WinEnter relativenumber.vim (nu = 1, rnu = 1)
BufLeave relativenumber.vim (nu = 1, rnu = 1)
BufEnter  (nu = 0, rnu = 0)
BufLeave  (nu = 0, rnu = 0)
"help.txt" [readonly] 253L, 9491B
BufEnter /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)
E492: Not an editor command: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
BufLeave /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)
WinLeave /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)
WinEnter relativenumber.vim (nu = 1, rnu = 1)
BufEnter relativenumber.vim (nu = 1, rnu = 1)

I don't understand a few things:

• Why do the first time I do :h and the second time generate different output?
• Why the sequence of events upon :h is WinLeave->WinEnter->BufLeave->BufEnter?
• Why upon :h I see that WinEnter relativenumber.vim (nu = 1, rnu = 1), considering nu and rnu are both off in :help?
• Why is there a buffer with no name, in the games?

---

The file I sourced before doing the 4 actions is the following

set nu
set rnu
augroup RelativeNumberOnlyInCurrentBuffer
  autocmd!
  autocmd BufEnter * echom 'BufEnter ' . expand('%') . ' (nu = ' . &nu . ', rnu = ' . &rnu . ')'
  autocmd BufLeave * echom 'BufLeave ' . expand('%') . ' (nu = ' . &nu . ', rnu = ' . &rnu . ')'
  autocmd WinEnter * echom 'WinEnter ' . expand('%') . ' (nu = ' . &nu . ', rnu = ' . &rnu . ')'
  autocmd WinLeave * echom 'WinLeave ' . expand('%') . ' (nu = ' . &nu . ', rnu = ' . &rnu . ')'
augroup END

Answer 1

When Vim opens help page it does the following:

1. Split current
2. Switch to new help buffer
3. Follow the tag

And so,

Why do the first time I do :h and the second time generate different output?

For the second time while following the tag (3) it is able to re-use the old help buffer. Therefore it has to leave from the buffer created at (2).

Why the sequence of events upon :h is WinLeave->WinEnter->BufLeave->BufEnter?

Because of (1), and then (2). This is the same way as :split another_file works.

Why upon :h I see that WinEnter relativenumber.vim (nu = 1, rnu = 1), considering nu and rnu are both off in :help?

Again, the same reason as in previous. You're still in the old buffer until the next BufEnter. Isn't that obvious from buffer name?!

Why is there a buffer with no name, in the games?

Because of (2). It just works like this.

Answer 2

WinLeave relativenumber.vim (nu = 1, rnu = 1)
WinEnter relativenumber.vim (nu = 1, rnu = 1)
BufLeave relativenumber.vim (nu = 1, rnu = 1)
BufEnter  (nu = 0, rnu = 0)
"help.txt" [readonly] 253L, 9491B
BufEnter /usr/share/vim/vim90/doc/help.txt (nu = 0, rnu = 0)

I'm not sure what's up with the empty buffer, but I suspect you would see something similar if you did :split and :edit somefile.

1. Split the window. Leaves the old window with the original file, enters a new window with the same file.
2. :edit or :buffer the new file, leaving the current buffer and entering a new one.

Hence, WinLeave -> WinEnter -> BufLeave -> BufEnter. I would be curious if the sequence is the same or different for :split file.