Re: diff attribute ignored by show and log -p

[Jeff King <peff@peff.net>]

On Thu, Dec 17, 2009 at 11:44:16AM -0500, Jay Soffian wrote:

> > The need to give --ext-diff is mentioned in 72909be (Add diff-option
> > --ext-diff, 2007-06-30) but its log message doesn't 'explain' why external
> > diff isn't used by default and you need to pass that extra option.
> 
> "To prevent funky games with external diff engines, git-log and
> friends prevent external diff engines from being called."
> 
> Seemed reason enough to me.

I don't remember discussing it at that time, but much later when
touching the external diff code and adding textconv, Junio and I came to
the conclusion that textconv was reasonable to do as part of "git log
-p", as the result is just an internal conversion that still results in
a text diff. Whereas an external diff might be terribly confusing, as it
could be spawning graphical viewers or producing output which does not
match well with the log output.

> > Probably --ext-diff should be the default?
> 
> Or available via a config option anyway.

If you were going to do such a config option, it might make sense to
make it an attribute of the diff driver rather than a global "use
external diff". Then each diff driver could say "Yes, I am reasonable to
be run as part of log -p".

-Peff