How can I determine if *any* window in the current tabpage is in diff-mode?

Question

So, I found this useful answer about iterating buffers; but due to the tabpage-specific duality of windows in Vim, I failed at adapting it to my needs.

Thus: how can I construct a boolean expression, determining whether or not any (not just the current) window in the tabpage is in &diff-mode?

Answer 1

You can sum up the values of &diff for each window, and see if the total is > 0:

let any_diff = 0
windo let any_diff += &diff
echo any_diff . ' windows in diff mode'
if any_diff > 0 | do stuff | endif

Answer 2

I don't like using windo that could trigger events if done without any caution, and thus I prefer using programmatic ways instead.

For instance, we can obtain the window numbers of the windows in diff mode with

:echo filter(range(1, winnr('$')), 'getwinvar(v:val, "&diff") == 1')