subtree: fix "git subtree split --rejoin"

"git merge" in v2.9 prevents merging unrelated histories.

"git subtree split --rejoin" creates unrelated histories when
creating a split repo from a raw sub-directory that did not
originate from an invocation of "git subtree add".

Restore the original behavior by passing --allow-unrelated-histories
when merging subtrees.  This ensures that the synthetic history
created by "git subtree split" can be merged.

Add a test to ensure that this feature works as advertised.

Reported-by: Brett Cundal <brett.cundal@iugome.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index 7a39b30..b567eae 100755 (executable)
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -662,6 +662,7 @@ cmd_split()
                debug "Merging split branch into HEAD..."
                latest_old=$(cache_get latest_old)
                git merge -s ours \
+                       --allow-unrelated-histories \
                        -m "$(rejoin_msg "$dir" $latest_old $latest_new)" \
                        $latest_new >&2 || exit $?
        fi

diff --git a/contrib/subtree/t/t7900-subtree.sh b/contrib/subtree/t/t7900-subtree.sh
index 7e8be5a..9751cfe 100755 (executable)
--- a/contrib/subtree/t/t7900-subtree.sh
+++ b/contrib/subtree/t/t7900-subtree.sh
@@ -347,6 +347,22 @@ test_expect_success 'split sub dir/ with --rejoin' '
  '
 
 next_test
+test_expect_success 'split sub dir/ with --rejoin from scratch' '
+       subtree_test_create_repo "$subtree_test_count" &&
+       test_create_commit "$subtree_test_count" main1 &&
+       (
+               cd "$subtree_test_count" &&
+               mkdir "sub dir" &&
+               echo file >"sub dir"/file &&
+               git add "sub dir/file" &&
+               git commit -m"sub dir file" &&
+               split_hash=$(git subtree split --prefix="sub dir" --rejoin) &&
+               git subtree split --prefix="sub dir" --rejoin &&
+               check_equal "$(last_commit_message)" "Split '\''sub dir/'\'' into commit '\''$split_hash'\''"
+       )
+ '
+
+next_test
 test_expect_success 'split sub dir/ with --rejoin and --message' '
        subtree_test_create_repo "$subtree_test_count" &&
        subtree_test_create_repo "$subtree_test_count/sub proj" &&