Re: log -p hides changes in merge commit

[Phillip Susi <psusi@cfl.rr.com>]

On 1/6/2011 4:04 PM, Jonathan Nieder wrote:
> In case (1), -c will show a "combined diff" for files where master
> does not match either the old master or topic.  --cc, on the other
> hand, will correctly suppress these uninteresting diffs.
> 
> In case (2), -c will show a noisy "combined diff" as before.
> --cc will show a combined diff when the changes from both parents
> touch nearby code, even if it merged trivially.
> 
> In case (3), -c and --cc will show the semantically boring but
> syntactically interesting merge.
> 
> Case (4) is underspecified.  So let's give a more precise example:
> the old master and topic tried to fix the same bug in two incompatible
> ways.  When merging, I decide I like the topic's way better, so I
> resolve conflicts in favor of the topic.  Hopefully all unrelated
> changes on master were preserved!
> 
> In this case, -c and --cc will very likely show nothing at all.
> Each file matches one of the two parents (old master or topic) so
> there is no easy way to distinguish the case from (0) or (1).

That does help me understand the difference between -c and -cc, but I
still don't see why one or the other is not the default behavior of log
-p, instead of opting to never show anything at all for merges?