From be011bbe001facf71bd636494eb253aa5151d26a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20=C3=85gren?= <martin.agren@gmail.com>
Date: Sat, 21 Apr 2018 00:12:31 +0200
Subject: fast-export: fix regression skipping some merge-commits
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7199203937 (object_array: add and use `object_array_pop()`, 2017-09-23)
noted that the pattern `object = array.objects[--array.nr].item` could
be abstracted as `object = object_array_pop(&array)`.

Unfortunately, one of the conversions was horribly wrong. Between
grabbing the last object (i.e., peeking at it) and decreasing the object
count, the original code would sometimes return early. The updated code
on the other hand, will always pop the last element, then maybe do the
early return without doing anything with the object.

The end result is that merge commits where all the parents have still
not been exported will simply be dropped, meaning that they will be
completely missing from the exported data.

Re-add a commit when it is not yet time to handle it. An alternative
that was considered was to peek-then-pop. That carries some risk with it
since the peeking and popping need to act on the same object, in a
concerted fashion.

Add a test that would have caught this.

Reported-by: Isaac Chou <Isaac.Chou@microfocus.com>
Analyzed-by: Isaac Chou <Isaac.Chou@microfocus.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 796d0cd..2fc3e76 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -651,8 +651,11 @@ static void handle_tail(struct object_array *commits, struct rev_info *revs,
 	struct commit *commit;
 	while (commits->nr) {
 		commit = (struct commit *)object_array_pop(commits);
-		if (has_unshown_parent(commit))
+		if (has_unshown_parent(commit)) {
+			/* Queue again, to be handled later */
+			add_object_array(&commit->object, NULL, commits);
 			return;
+		}
 		handle_commit(commit, revs, paths_of_changed_objects);
 	}
 }
diff --git a/t/t9350-fast-export.sh b/t/t9350-fast-export.sh
index 866ddf6..c699c88 100755
--- a/t/t9350-fast-export.sh
+++ b/t/t9350-fast-export.sh
@@ -540,4 +540,22 @@ test_expect_success 'when using -C, do not declare copy when source of copy is a
 	test_cmp expected actual
 '
 
+test_expect_success 'merge commit gets exported with --import-marks' '
+	test_create_repo merging &&
+	(
+		cd merging &&
+		test_commit initial &&
+		git checkout -b topic &&
+		test_commit on-topic &&
+		git checkout master &&
+		test_commit on-master &&
+		test_tick &&
+		git merge --no-ff -m Yeah topic &&
+
+		echo ":1 $(git rev-parse HEAD^^)" >marks &&
+		git fast-export --import-marks=marks master >out &&
+		grep Yeah out
+	)
+'
+
 test_done
-- 
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