Re: feature suggestion: optimize common parts for checkout --conflict=diff3

Junio C Hamano [off-list ref] writes:

You could make it "1234<AB|5=AX><C|=C><DE|6=YE>789", and that is
technically correct (what there were in the shared original for the
conflicted part is 5 and then 6), but the representation pretends
that it knows more than there actually is information, which may be
somewhat misleading.  All these three are equally plausible split of
the original "56":

	1234<AB|=AX><C|=C><DE|56=YE>789
	1234<AB|5=AX><C|=C><DE|6=YE>789
	1234<AB|56=AX><C|=C><DE|=YE>789

and picking one over others would be a mere heuristic.  All three
are technically correct representations and it is just the matter of
which one is the easiest to understand.  So, this is the kind of
"misleading but not incorrect".

I forgot to say that youu could even do something silly like:

	1234<AB|=AX><C|56=C><DE|=YE>789

;-)

In all these cases, the middle part would look like this:

      <<<<<<< ours
      C
      ||||||| base
      =======
      C
      >>>>>>> theirs

in order to honor the explicit "I want to view all three versions to
examine the situation" aka "--conflict=diff3" option.  We cannot
reduce it to just "C".  That will make it "not just misleading but
is actively wrong".

I also forgot to say that the issue is the same to reduce

 	1234<AB|=AX><C|=C><DE|56=YE>789

to

 	1234<A|=A><B|=X><C|=C><D|56=Y><E|=E>789

which is unconditionally correct and then for all x reduce <x|=x> to
x, yielding

 	1234A<B|=X>C<D|56=Y>E789

which your zealous-diff3 would do.  So squashing that <C|=C> in the
middle would be consistent if you take the zealous-diff3 route.

But again, that is discarding the information of the original, which
the user explicitly asked from "diff3 -m", i.e. show all three to
examine the situation. If the user wants to operate _without_ the
original, the user would have asked for "RCS merge" style output, so
I am still not sure if that is a sensible mode of operation for diff3
to begin with.