merge-recur status

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

with my last patches, I tested merge-recur on 'next' (46faaaf8) by 
comparing the index after -recur and -recursive, respectively.

At this stage, there are 1017 merges with exactly two parents (which is 
the only type of merge -recursive can handle).

For all but 9 of them, the indices where identical. The reason for those 9 
to differ: the order of the merge-bases. -recursive does its own thing 
(set intersection after traversing the commits by hand, probably in 
topological order), whereas with the last patches, -recur orders them by 
decreasing date.

The 9 cases are:

52bc0e29: 1 better
a5c8a98c: 1 better, 2 identical
63bccad3: 1 identical
dcaad49c: 3 identical
7f2d5cb5: 3 identical
c2b9e699: 2 identical
4cc0b8a4: 2 identical
d2b9b5f5: 1 identical
41094b8e: worse

where

- "1 better" means that -recursive has a conflicting hunk, where 
  -recur resolves it (it is identical with the commit),

- "1 identical" means that there were multiply conflicting hunks (meaning 
  that merging two merge-bases already conflicted, and another conflict 
  came on top), and the versions of -recursive and -recur differ only in 
  the order of the conflict nesting, and

- "worse" means that the merge of 859ab4c and 061ad5f, which _should_ have 
  resulted in 41094b8e (as with -recursive) resulted in a

  "fatal: Entry 'epoch.c' would be overwritten by merge. Cannot merge."

  It might have its reason in the fact that 859ab4c and 061ad5f have
  8 (!) merge bases.

Now, on average, -recur takes 0.1 seconds on average, spending only 9.9% 
of what -recursive takes (on average). So I am happy with the speed.

I think -recur is really really close to being trustworthy, _but_ I do not 
understand the reason behind the error. It happens in line 614 of 
unpack-trees.c, where the "index" contains epoch.c, and "index" and 
"remote" are identical, but "head" is empty.

I tried to wrap my head over it, but seem unable to do so. Also, I do not 
find the case 14ALT (which is mentioned in unpack-trees.c:603) in 
Documentation/technical/trivial-merge.txt.

Help?

Ciao,
Dscho