Force merge tool to run on any change

[Matt Mackall]

On Thu, 2015-10-22 at 10:26 +0100, Pierre-Yves David wrote:
> 
> On 10/22/2015 10:11 AM, Andrew Lentvorski wrote:
> > I'm trying to force kdiff3 to run for differences *no matter
> > what*.  Unfortunately, something is short circuiting me.
> > 
> > I don't want a quiet merge.  I want to pop open kdiff3 *for even
> > the most trivial change--even if only one of the files changed
> > --even if its just whitespace*, and I'm absolutely pulling my hair
> > out.  I've turned off premerge.  I've changed the args so that
> > there is no "-auto" on the line, and I still can't get kdiff3 to
> > pop open.
> > 
> > I'm sure it's something stupid, but apparently my google-fu is too
> > low level.
> 
> Premerge happens in all case no matter what. The 'premerge' config
> for 
> tool only control if the premerge result should be kept.

This is incorrect:

https://selenic.com/hg/file/tip/mercurial/filemerge.py#l214

If premerge is false, we'll skip it entirely. However:

a) we'll never invoke a merge tool if there's a change on only one
branch, we'll simply take the changed version

b) kdiff3 has its own premerge that we turn on:

       --auto    No GUI if all conflicts are auto-solvable. (Needs -o file)

-- 
Mathematics is the supreme nostalgia of our time.