[PATCH v3] refuse to merge during a merge

[Clemens Buchacher <drizzd@aon.at>]

The following is an easy mistake to make for users coming from version
control systems with an "update and commit"-style workflow.

        1. git pull
        2. resolve conflicts
        3. git pull

Step 3 overrides MERGE_HEAD, starting a new merge with dirty index.
IOW, probably not what the user intended. Instead, refuse to merge
again if a merge is in progress.

Reported-by: Dave Olszewski <cxreg@pobox.com>
Signed-off-by: Clemens Buchacher <drizzd@aon.at>
---

On Sun, May 31, 2009 at 12:36:37PM -0700, Junio C Hamano wrote:
> For example, "git merge" may learn "git merge --abort" like other commands
> that have "attempt, stop, let the user fix up to conclude" modes of
> operations (i.e. rebase and am), and we may suggest to use that to recover
> in the message, instead of 'git reset'.  But that can only be used if we
> stopped because we saw MERGE_HEAD; you definitely do not want to suggest
> "git merge --abort" if the index is unmerged due to a conflicted rebase in
> progress.

Indeed. I wasn't thinking.

Clemens

 builtin-merge.c            |    5 ++++-
 t/t3030-merge-recursive.sh |    3 +++
 2 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/builtin-merge.c b/builtin-merge.c
index 0b58e5e..9e9bd52 100644
--- a/builtin-merge.c
+++ b/builtin-merge.c
@@ -836,8 +836,11 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	struct commit_list **remotes = &remoteheads;
 
 	setup_work_tree();
+	if (file_exists(git_path("MERGE_HEAD")))
+		die("You have not concluded your merge. (MERGE_HEAD exists)");
 	if (read_cache_unmerged())
-		die("You are in the middle of a conflicted merge.");
+		die("You are in the middle of a conflicted merge."
+				" (index unmerged)");
 
 	/*
 	 * Check if we are _not_ on a detached HEAD, i.e. if there is a
diff --git a/t/t3030-merge-recursive.sh b/t/t3030-merge-recursive.sh
index 0de613d..9b3fa2b 100755
--- a/t/t3030-merge-recursive.sh
+++ b/t/t3030-merge-recursive.sh
@@ -276,6 +276,9 @@ test_expect_success 'fail if the index has unresolved entries' '
 
 	test_must_fail git merge "$c5" &&
 	test_must_fail git merge "$c5" 2> out &&
+	grep "You have not concluded your merge" out &&
+	rm -f .git/MERGE_HEAD &&
+	test_must_fail git merge "$c5" 2> out &&
 	grep "You are in the middle of a conflicted merge" out
 
 '
-- 
1.6.3.1.147.g637c3