Re: git-merge segfault in 1.6.6 and master

Junio C Hamano [off-list ref] writes:

After I stared at the code for more than two hours, I gave up trying to
diagnose this by myself.  People more familiar with the merge-recursive
implementation might be able to help figuring this out and may prove my
suspicion wrong, but I have a feeling that without a fairly big rewrite
the code is unsalvageable.

In the meantime, I think applying this patch is the right thing to do.

-- >8 --
Subject: merge-recursive: do not return NULL only to cause segfault

merge-recursive calls write_tree_from_memory() to come up with a virtual
tree, with possible conflict markers inside the blob contents, while
merging multiple common ancestors down.  It is a bug to call the function
with unmerged entries in the index, even if the merge to come up with the
common ancestor resulted in conflicts.  Otherwise the result won't be
expressible as a tree object.

We _might_ want to suggest the user to set GIT_MERGE_VERBOSITY to 5 and
re-run the merge in the message.  At least we will know which part of
process_renames() or process_entry() functions is not correctly handling
the unmerged paths, and it might help us diagnosing the issue.

Signed-off-by: Junio C Hamano <redacted>
---
 merge-recursive.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index 1239647..cb53b01 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c

@@ -202,14 +202,14 @@ struct tree *write_tree_from_memory(struct merge_options *o)
 
 	if (unmerged_cache()) {
 		int i;
-		output(o, 0, "There are unmerged index entries:");
+		fprintf(stderr, "BUG: There are unmerged index entries:\n");
 		for (i = 0; i < active_nr; i++) {
 			struct cache_entry *ce = active_cache[i];
 			if (ce_stage(ce))
-				output(o, 0, "%d %.*s", ce_stage(ce),
-				       (int)ce_namelen(ce), ce->name);
+				fprintf(stderr, "BUG: %d %.*s", ce_stage(ce),
+					(int)ce_namelen(ce), ce->name);
 		}
-		return NULL;
+		die("Bug in merge-recursive.c");
 	}
 
 	if (!active_cache_tree)