What is the order of WinEnter, BufEnter, BufRead, Syntax, FileType events?

Question

I've gone through the autocmd.txt help, but the information about this is scattered and not always present (eg. with BufRead).

Could someone who understands this well list the order of these events - with perhaps the conditions marked in parantheses, like

WinEnter   
BufEnter (if this window is for a different buffer than the current)

and so on, for easy reference?

Note ^{(copied from my own comment below)}: I'm not talking about individual explanations of them, which are OK, but about how they interact with one another and in what order they happen. For eg., WinEnter says "Vim executes the BufEnter autocommands after the WinEnter autocommands", TabEnter says "After triggering the WinEnter and before triggering the BufEnter event", it's all scattered like this into many places. And sometimes it's not mentioned at all (for eg. BufRead doesn't mention whether it runs after BufEnter or before - maybe an expert can infer it from some other piece of info there, but I can't.
So, my intent here is to create a single, simple reference for the order of these events that can be looked up quickly by non-experts, in order to be more precise in our autocmd event specifications.

Answer 1

I tried googling for this with different sets of keywords, and struck gold on one such attempt with this result: https://web.archive.org/web/20220121051339/https://developer.ibm.com/tutorials/l-vim-script-5/

Specifically, this part is relevant to the current question:

For example, if you start Vim, edit a file named demo.txt, swap into Insert mode, type in some text, save the file, and then exit, your Vim session receives a series of events like what is shown in Listing 1.

Listing 1. Event sequence in a simple Vim editing session

> vim

1. BufWinEnter (create a default window)
2. BufEnter (create a default buffer)
3. VimEnter (start the Vim session):edit demo.txt
4. BufNew (create a new buffer to contain demo.txt)
5. BufAdd (add that new buffer to the session’s buffer list)
6. BufLeave (exit the default buffer)
7. BufWinLeave (exit the default window)
8. BufUnload (remove the default buffer from the buffer list)
9. BufDelete (deallocate the default buffer)
10. BufReadCmd (read the contexts of demo.txt into the new buffer)
11. BufEnter (activate the new buffer)
12. BufWinEnter (activate the new buffer's window)i
13. InsertEnter (swap into Insert mode)

It's still not entirely comprehensive (eg. no mention of BufRead aka BufReadPost, but I'm assuming it would come after BufReadCmd), but it's an excellent start.

One crucial missing piece of information though is how the FileType and Syntax autocmd events interact with this (assuming filetype and syntax are already on, and a new file is opened whose filetype and syntax are known to Vim).

Answer 2

To complete the @sundar answer:

You can log the order of the events simply with a logging function:

augroup EventLoggin
  autocmd!
  autocmd BufNewFile * call s:Log('BufNewFile')
  autocmd BufReadPre * call s:Log('BufReadPre')
  ...
  autocmd User * call s:Log('User')
augroup END

function! s:Log(eventName) abort
  silent execute '!echo '.a:eventName.' >> log'
endfunction

See the full file here: https://github.com/lervag/dotvim/blob/3aa56d621423540bfa26b330182b3e97ed4ee5e8/personal/plugin/log-autocmds.vim (NB: As the previous gist has disappeared, I've replaced the URL to Karl's plugin --Luc)

You can then tail -f log and you get a real-time autocommand events activity.

Answer 3

This is the first result show up on google search about 'Vim event order'. So, i think it's worth providing the actual answer.

Using the command from @nobe4 answer, this is the result:

1. Opening a new file, insert letter 'a', write and quit.

Syntax
User
BufNewFile
FileType
Syntax
BufWinEnter
BufEnter
VimEnter
CursorMoved
FocusGained
InsertEnter
CursorHoldI
InsertCharPre
CursorMovedI
TextChangedI
InsertLeave
CursorMoved
CmdlineEnter
CmdlineChanged
CmdlineChanged
CmdlineLeave
BufWrite
BufWritePre
BufWritePost
QuitPre
ExitPre
BufWinLeave
BufUnload
VimLeavePre
BufNew
BufNew
VimLeave

2. Opening an existing file, append letter 'a', write and quit.

Syntax
User
BufReadPre
BufRead
BufReadPost
FileType
Syntax
BufWinEnter
BufEnter
VimEnter
CursorMoved
FocusGained
InsertEnter
CursorMovedI
InsertCharPre
CursorMovedI
TextChangedI
InsertLeave
CursorMoved
CmdlineEnter
CmdlineChanged
CmdlineChanged
CmdlineLeave
BufWrite
BufWritePre
BufWritePost
QuitPre
ExitPre
BufWinLeave
BufUnload
VimLeavePre
BufNew
BufNew
VimLeave

3. Opening a new file, write and quit.

Syntax
User
BufNewFile
FileType
Syntax
BufWinEnter
BufEnter
VimEnter
CursorMoved
FocusGained
CmdlineEnter
CmdlineChanged
CmdlineChanged
CmdlineLeave
BufWrite
BufWritePre
BufWritePost
QuitPre
ExitPre
BufWinLeave
BufUnload
VimLeavePre
BufNew
BufNew
VimLeave