Re: "fatal: Untracked working tree file 'so-and-so' would be overwritten by merge"

Linus Torvalds [off-list ref] writes:

Hmm. I'm getting this message annoyingly often, simply because a few files 
that used to be tracked are now generated, and so they exist in my tree 
but are no longer tracked.

However, they may be tracked in an older tree that I pull, because in that 
older tree they _do_ exist, and we get the

	fatal: Untracked working tree file 'so-and-so' would be overwritten by merge.

which is actually incorrect, because the merge result will not even 
_contain_ that untracked file any more.

So the message is misleading - we should only consider this a fatal thing 
if we actually do generate that file as part of a git-read-tree, but if a 
merge won't touch a file, it shouldn't be "overwritten".

It's true that if the _other_ end actually removed a file that we used to 
have (ie the file _disappears_ as part of the merge), then we should 
verify that that file matched what we're going to remove, but if the old 
index didn't contain the file at all, and the new index won't contain it 
either, it really should be a no-op.

True.

I think it is verify_absent() on l.665 in threeway_merge().

	if (index) {
		verify_uptodate(index, o);
	}
	else if (path)
		verify_absent(path, "overwritten", o);

	o->nontrivial_merge = 1;

We say "we know this path is involved in the non-trivial merge;
if the current index has it, it had better be up-to-date" (the
first "if").  I think that up to that check is fine.

However, we say that otherwise, the path should not exist in the
working tree; this should not be done unconditionally.  As you
say, the check should depend on the merge result.

But that is a bit tricky.  This is not on the aggressive path,
and the merge result is decided by the policy implemented by the
caller of read-tree.  So in that sense we should not be doing
the working tree check ourselves either.  We just should leave
that to the caller.

Hence, I think removing the above "else if" part altogether is
the right thing to do here.

---

diff --git a/unpack-trees.c b/unpack-trees.c
index 3ac0289..b1d78b8 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c

@@ -661,8 +661,6 @@ int threeway_merge(struct cache_entry **
 	if (index) {
 		verify_uptodate(index, o);
 	}
-	else if (path)
-		verify_absent(path, "overwritten", o);
 
 	o->nontrivial_merge = 1;