Re: two-way merge corner case bug

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Jeff King <peff@xxxxxxxx> writes:

> On Tue, Feb 26, 2013 at 12:06:42PM -0800, Junio C Hamano wrote:
>
>> It seems that we have a corner case bug in two-way merge to reset
>> away the conflicts with "read-tree -u --reset HEAD ORIG_HEAD".
>
> Isn't this a repeat of:
>
>   http://thread.gmane.org/gmane.comp.version-control.git/202440/focus=212316
>
> whose fix never got finalized? It's on my todo list, but it seems that
> items keep sinking further down on that list, rather than getting
> completed. :-/

Yeah, I think the patch in your message is a good starting point to
solve a half of the issue (i.e. unmerged current one should be
replaced with the version from the "going to" tree).  Attached is
with a slight update.

The other half that is not solved by this patch is that we will lose
Z because merge-recursive removed it when it renamed it and left
three stages for A in the index, and to "read-tree --reset -u HEAD
ORIG_HEAD", it looks as if you removed Z yourself while on HEAD and
want to carry your local change forward to ORIG_HEAD.

I think this too needs to be fixed.  We are saying "-u --reset" to
mean "I want to go there no matter what", not "-u -m" that means "I
am carrying my changes forward while checking out another branch".

 unpack-trees.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 09e53df..3d17108 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1748,14 +1748,23 @@ int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
 		newtree = NULL;
 
 	if (current) {
-		if ((!oldtree && !newtree) || /* 4 and 5 */
-		    (!oldtree && newtree &&
-		     same(current, newtree)) || /* 6 and 7 */
-		    (oldtree && newtree &&
-		     same(oldtree, newtree)) || /* 14 and 15 */
-		    (oldtree && newtree &&
-		     !same(oldtree, newtree) && /* 18 and 19 */
-		     same(current, newtree))) {
+		if (current->ce_flags & CE_CONFLICTED) {
+			if (same(oldtree, newtree) || o->reset) {
+				if (!newtree)
+					return deleted_entry(current, current, o);
+				else
+					return merged_entry(newtree, current, o);
+			}
+			return o->gently ? -1 : reject_merge(current, o);
+		}
+		else if ((!oldtree && !newtree) || /* 4 and 5 */
+			 (!oldtree && newtree &&
+			  same(current, newtree)) || /* 6 and 7 */
+			 (oldtree && newtree &&
+			  same(oldtree, newtree)) || /* 14 and 15 */
+			 (oldtree && newtree &&
+			  !same(oldtree, newtree) && /* 18 and 19 */
+			  same(current, newtree))) {
 			return keep_entry(current, o);
 		}
 		else if (oldtree && !newtree && same(current, oldtree)) {
--
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