autocommand within conditional autocommand

Question

I have an autocommand that is supposed to register a different autocommand whenever I enter a buffer where a certain condition is met:

let w:contextlist_open = 1

augroup LaunchShowContext
    autocmd!
    autocmd BufEnter * 
        \ if (exists("w:contextlist_open") && w:contextlist_open == 1) 
            \ | :autocmd CursorHold * call ShowContext()
        \ | endif
augroup END

If I fire up another buffer and switch back and forth, I get Error detected while processing CursorHold Autocommands for "*": E580: :endif without :if: endif. I suspect this is because Vim thinks the endif belongs with the second autocommand rather than the first, and I'm not sure how to make it so that it goes with the correct one. I tried wrapping the autocmd CursorHold * call ShowContext() in parentheses, but that seems to give me other problems.

Answer 1

Use :execute like this:

augroup LaunchShowContext | au!
    autocmd BufEnter *
        \ if get(w:, 'contextlist_open')
            \ | execute 'autocmd! CursorHold <buffer> call ShowContext()'
        \ | endif
augroup end

But note (at least) three problems:

1) You examine window-variable contextlist_open, while expecting buffer-specific event CursorHold to fire. That could be frustrating if your buffer is shown in several split windows.

2) unlet-ting contextlist_open will not remove au CursorHold, as one would expect.

3) execute will run under global augroup context, so you still must find a way to prevent repeating call ShowContext()'s due to multiple BufEnter events. I put au! for simplicity, but that could potentially conflict with other plugins, so you probably should explore another solution (create another augroup mygroup then check if exists('#mygroup#CursorHold#<buffer>') etc.).