[PATCH 09/10] cherry-pick: add a label for ancestor

[Jonathan Nieder <jrnieder@gmail.com>]

git cherry-pick and git revert will present conflict hunks in output
something like what ‘diff3 -m’ produces if the merge.conflictstyle
configuration option is set to diff3.

Unfortunately, some tools reportedly cannot parse the conflict hunks
because of a small difference from diff3: diff3 -m includes a label
for the merge base on the ||||||| line.  Humans parsing the conflict
hunks by hand might want to know what the common ancestor represents,
too.  So mark the start of the text from the parent of the commit
being cherrypicked (resp. from the commit being reverted) with the
label "parent".

It would be nicer to use a more informative label, and that might
happen in the future.

git rerere will not have trouble parsing this output, since instead of
looking for a newline, it looks for whitespace after the |||||||
marker.  No other code in git tries to parse conflict hunks.

Reported-by: Stefan Monnier <monnier@iro.umontreal.ca>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
In the revert case, this gives

 <<<<<<< HEAD
 foo
 ||||||| parent
 bar
 =======
 baz
 >>>>>>> ab78c93 "Make some change we would like to revert"

This is a bit misleading, since actually “baz” is from the commit
to revert’s parent and “bar” is from the commit to revert.

Probably the labels should be switched.  I didn’t do this because
it is late and it would have been a larger change from the current
behavior.

It also would be nice to suppress the ancestor and do a two-way
merge when cherry-picking a root commit.  I haven’t yet looked into
how hard this would be.

 builtin/revert.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/builtin/revert.c b/builtin/revert.c
index eff5268..a61dd9a 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -372,6 +372,7 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 
 	read_cache();
 	init_merge_options(&o);
+	o.ancestor = base ? "parent" : "(empty tree)";
 	o.branch1 = "HEAD";
 	o.branch2 = oneline;
 
-- 
1.7.0