RE: show whitespace problems by default in diff-mode

[Drew Adams]

> diff-mode is set up to show trailing whitespace problems, but it's not
> doing it by default, to enable this one has to do:
> 
> (add-hook 'diff-mode-hook 'whitespace-mode)
> 
> Vinicius also posted a patch to edit files to clean the trailing
> whitespace problems based on the diff.
> 
> Why not turn on whitespace-mode by default in diff-mode?  It makes
> spotting whitespace problems very easy, and will make it also easy to
> fix.

Perhaps for the same reason that whitespace diffs are ignored by default by
`diff' - because whitespace differences (including trailing whitespace) are
often _not_ so interesting.

What's the problem with setting `diff' switches and adding `whitespace-mode' to
the hook the way you want? Why should the default value change? When you "make
spotting whitespace problems very easy" you also make ignoring whitespace
problems more difficult.

I don't have a particular axe to grind, here. It's just not clear that most
people will want to show whitespace diffs (or even trailing whitespace) most of
the time. If you can support that claim, then sure, go for it.