recursive submodules: detach HEAD from new state

When a submodule is on a branch and in its superproject you run a
recursive checkout, the branch of the submodule is updated to what the
superproject checks out. This is very unexpected in the current model of
Git as e.g. 'submodule update' always detaches the submodule HEAD.

Despite having plans to have submodule HEADS not detached in the future,
the current behavior is really bad as it doesn't match user expectations
and it is not checking for loss of commits (only to be recovered via the
reflog).

Detach the HEAD unconditionally in the submodule when updating it.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/submodule.c b/submodule.c
index 6531c5d6094e47b251e69ce741699abfee7a64df..37f4a9287284bbbb434f31170eaf276c0ee0175e 100644 (file)
--- a/submodule.c
+++ b/submodule.c
@@ -1641,7 +1641,8 @@ int submodule_move_head(const char *path,
                        cp.dir = path;
 
                        prepare_submodule_repo_env(&cp.env_array);
-                       argv_array_pushl(&cp.args, "update-ref", "HEAD", new, NULL);
+                       argv_array_pushl(&cp.args, "update-ref", "HEAD",
+                                        "--no-deref", new, NULL);
 
                        if (run_command(&cp)) {
                                ret = -1;

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 2d26f86800906ab1783edf10e7196adadd5f4af7..fc406b95d7f4c6041fdc2184ac10a2ddbc096851 100755 (executable)
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -848,6 +848,23 @@ test_submodule_switch_recursing_with_args () {
                        test_submodule_content sub1 origin/add_sub1
                )
        '
+       test_expect_success "$command: submodule branch is not changed, detach HEAD instead" '
+               prolog &&
+               reset_work_tree_to_interested add_sub1 &&
+               (
+                       cd submodule_update &&
+                       git -C sub1 checkout -b keep_branch &&
+                       git -C sub1 rev-parse HEAD >expect &&
+                       git branch -t check-keep origin/modify_sub1 &&
+                       $command check-keep &&
+                       test_superproject_content origin/modify_sub1 &&
+                       test_submodule_content sub1 origin/modify_sub1 &&
+                       git -C sub1 rev-parse keep_branch >actual &&
+                       test_cmp expect actual &&
+                       test_must_fail git -C sub1 symbolic-ref HEAD
+               )
+       '
+
        # Replacing a tracked file with a submodule produces a checked out submodule
        test_expect_success "$command: replace tracked file with submodule checks out submodule" '
                prolog &&