t7605: add a testcase demonstrating a bug with trivial merges

Repeating a trivial merge more than once will leave the index out of
sync, despite being clean before the merge and operating on the
exact same heads as the first run.  The recorded merge has the
correct tree and the working tree is brought up to date, it is just
the index that is left as it was before the merge.  Every attempt to
repeat the merge beyond the first will leave the index in the same
weird out-of-sync state.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/t7605-merge-resolve.sh b/t/t7605-merge-resolve.sh
index 0cb9d11f2171de19b260391017310f0ee792f89b..2f80037c9a814e5a1de266843d7eedfa37fd0b6a 100755 (executable)
--- a/t/t7605-merge-resolve.sh
+++ b/t/t7605-merge-resolve.sh
@@ -27,7 +27,7 @@ test_expect_success 'setup' '
        git tag c3
 '
 
-test_expect_success 'merge c1 to c2' '
+merge_c1_to_c2_cmds='
        git reset --hard c1 &&
        git merge -s resolve c2 &&
        test "$(git rev-parse c1)" != "$(git rev-parse HEAD)" &&
@@ -41,6 +41,10 @@ test_expect_success 'merge c1 to c2' '
        test 3 = $(git ls-files | wc -l)
 '
 
+test_expect_success 'merge c1 to c2'        "$merge_c1_to_c2_cmds"
+
+test_expect_failure 'merge c1 to c2, again' "$merge_c1_to_c2_cmds"
+
 test_expect_success 'merge c2 to c3 (fails)' '
        git reset --hard c2 &&
        test_must_fail git merge -s resolve c3