merge-recursive: avoid incorporating uncommitted changes in a merge

builtin/merge.c contains this important requirement for merge strategies:
	/*
	 * At this point, we need a real merge.  No matter what strategy
	 * we use, it would operate on the index, possibly affecting the
	 * working tree, and when resolved cleanly, have the desired
	 * tree in the index -- this means that the index must be in
	 * sync with the head commit.  The strategies are responsible
	 * to ensure this.
	 */

merge-recursive does not do this check directly, instead it relies on
unpack_trees() to do it.  However, merge_trees() has a special check for
the merge branch exactly matching the merge base; when it detects that
situation, it returns early without calling unpack_trees(), because it
knows that the HEAD commit already has the correct result.  Unfortunately,
it didn't check that the index matched HEAD, so after it returned, the
outer logic ended up creating a merge commit that included something
other than HEAD.

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

diff --git a/merge-recursive.c b/merge-recursive.c
index 9fb0b9f8fdfe12b58b5876a4984f4bf9a9f5c0fb..be01f528cb4849fc68c7f082e1d65709f86147d5 100644 (file)
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1952,6 +1952,13 @@ int merge_trees(struct merge_options *o,
        }
 
        if (oid_eq(&common->object.oid, &merge->object.oid)) {
+               struct strbuf sb = STRBUF_INIT;
+
+               if (index_has_changes(&sb)) {
+                       err(o, _("Dirty index: cannot merge (dirty: %s)"),
+                           sb.buf);
+                       return 0;
+               }
                output(o, 0, _("Already up to date!"));
                *result = head;
                return 1;

diff --git a/t/t6044-merge-unrelated-index-changes.sh b/t/t6044-merge-unrelated-index-changes.sh
index 5e472be92b7c9cec264556b25d0f9bc0c7e0f530..23b86fb9778980ab813d5e252065ebe34fe4736d 100755 (executable)
--- a/t/t6044-merge-unrelated-index-changes.sh
+++ b/t/t6044-merge-unrelated-index-changes.sh
@@ -112,7 +112,7 @@ test_expect_success 'recursive' '
        test_must_fail git merge -s recursive C^0
 '
 
-test_expect_failure 'recursive, when merge branch matches merge base' '
+test_expect_success 'recursive, when merge branch matches merge base' '
        git reset --hard &&
        git checkout B^0 &&