sequencer: allow introducing new root commits

In the context of the new --rebase-merges mode, which was designed
specifically to allow for changing the existing branch topology
liberally, a user may want to extract commits into a completely fresh
branch that starts with a newly-created root commit.

This is now possible by inserting the command `reset [new root]` before
`pick`ing the commit that wants to become a root commit. Example:

	reset [new root]
	pick 012345 a commit that is about to become a root commit
	pick 234567 this commit will have the previous one as parent

This does not conflict with other uses of the `reset` command because
`[new root]` is not (part of) a valid ref name: both the opening bracket
as well as the space are illegal in ref names.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/sequencer.c b/sequencer.c
index 8eddda681d14a102ee95f33c60c38aa42f16264c..a7832399b1f324560d4b18822eb8665b4a7a050b 100644 (file)
--- a/sequencer.c
+++ b/sequencer.c
@@ -2747,18 +2747,34 @@ static int do_reset(const char *name, int len, struct replay_opts *opts)
        if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
                return -1;
 
-       /* Determine the length of the label */
-       for (i = 0; i < len; i++)
-               if (isspace(name[i]))
-                       len = i;
-
-       strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
-       if (get_oid(ref_name.buf, &oid) &&
-           get_oid(ref_name.buf + strlen("refs/rewritten/"), &oid)) {
-               error(_("could not read '%s'"), ref_name.buf);
-               rollback_lock_file(&lock);
-               strbuf_release(&ref_name);
-               return -1;
+       if (len == 10 && !strncmp("[new root]", name, len)) {
+               if (!opts->have_squash_onto) {
+                       const char *hex;
+                       if (commit_tree("", 0, the_hash_algo->empty_tree,
+                                       NULL, &opts->squash_onto,
+                                       NULL, NULL))
+                               return error(_("writing fake root commit"));
+                       opts->have_squash_onto = 1;
+                       hex = oid_to_hex(&opts->squash_onto);
+                       if (write_message(hex, strlen(hex),
+                                         rebase_path_squash_onto(), 0))
+                               return error(_("writing squash-onto"));
+               }
+               oidcpy(&oid, &opts->squash_onto);
+       } else {
+               /* Determine the length of the label */
+               for (i = 0; i < len; i++)
+                       if (isspace(name[i]))
+                               len = i;
+
+               strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
+               if (get_oid(ref_name.buf, &oid) &&
+                   get_oid(ref_name.buf + strlen("refs/rewritten/"), &oid)) {
+                       error(_("could not read '%s'"), ref_name.buf);
+                       rollback_lock_file(&lock);
+                       strbuf_release(&ref_name);
+                       return -1;
+               }
        }
 
        memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));

diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index 3d4dfdf7bec7db74eb41bd7606c13629f6abc370..35260862fcb759c9f29ded4fcf3ba0f19628631b 100755 (executable)
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -241,4 +241,38 @@ test_expect_success 'refuse to merge ancestors of HEAD' '
        test_cmp_rev HEAD $before
 '
 
+test_expect_success 'root commits' '
+       git checkout --orphan unrelated &&
+       (GIT_AUTHOR_NAME="Parsnip" GIT_AUTHOR_EMAIL="root@example.com" \
+        test_commit second-root) &&
+       test_commit third-root &&
+       cat >script-from-scratch <<-\EOF &&
+       pick third-root
+       label first-branch
+       reset [new root]
+       pick second-root
+       merge first-branch # Merge the 3rd root
+       EOF
+       test_config sequence.editor \""$PWD"/replace-editor.sh\" &&
+       test_tick &&
+       git rebase -i --force --root -r &&
+       test "Parsnip" = "$(git show -s --format=%an HEAD^)" &&
+       test $(git rev-parse second-root^0) != $(git rev-parse HEAD^) &&
+       test $(git rev-parse second-root:second-root.t) = \
+               $(git rev-parse HEAD^:second-root.t) &&
+       test_cmp_graph HEAD <<-\EOF &&
+       *   Merge the 3rd root
+       |\
+       | * third-root
+       * second-root
+       EOF
+
+       : fast forward if possible &&
+       before="$(git rev-parse --verify HEAD)" &&
+       test_might_fail git config --unset sequence.editor &&
+       test_tick &&
+       git rebase -i --root -r &&
+       test_cmp_rev HEAD $before
+'
+
 test_done