Merge branch 'js/sequencer-and-root-commits'

The implementation of "git rebase -i --root" has been updated to use
the sequencer machinery more.

* js/sequencer-and-root-commits:
  rebase --rebase-merges: root commits can be cousins, too
  rebase --rebase-merges: a "merge" into a new root is a fast-forward
  sequencer: allow introducing new root commits
  rebase -i --root: let the sequencer handle even the initial part
  sequencer: learn about the special "fake root commit" handling
  sequencer: extract helper to update active_cache_tree

git-rebase--interactive.sh

@@ -894,6 +894,8 @@ init_revisions_and_shortrevisions () {
 	else
 		revisions=$onto...$orig_head
 		shortrevisions=$shorthead
+		test -z "$squash_onto" ||
+		echo "$squash_onto" >"$state_dir"/squash-onto
 	fi
 }
@@ -948,7 +950,7 @@ EOF
 	die "Could not skip unnecessary pick commands"
 	checkout_onto
-	if test -z "$rebase_root" && test ! -d "$rewritten"
+	if test ! -d "$rewritten"
 	then
 		require_clean_work_tree "rebase"
 		exec git rebase--helper ${force_rebase:+--no-ff} $allow_empty_message \

sequencer.c

@@ -123,6 +123,12 @@ static GIT_PATH_FUNC(rebase_path_rewritten_list, "rebase-merge/rewritten-list")
 static GIT_PATH_FUNC(rebase_path_rewritten_pending,
 	"rebase-merge/rewritten-pending")
+/*
+ * The path of the file containig the OID of the "squash onto" commit, i.e.
+ * the dummy commit used for `reset [new root]`.
+ */
+static GIT_PATH_FUNC(rebase_path_squash_onto, "rebase-merge/squash-onto")
+
 /*
  * The path of the file listing refs that need to be deleted after the rebase
  * finishes. This is used by the `label` command to record the need for cleanup.
@@ -469,7 +475,8 @@ static int fast_forward_to(const struct object_id *to, const struct object_id *f
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD",
-				   to, unborn ? &null_oid : from,
+				   to, unborn && !is_rebase_i(opts) ?
+				   &null_oid : from,
 				   0, sb.buf, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
 		ref_transaction_free(transaction);
@@ -561,9 +568,23 @@ static int do_recursive_merge(struct commit *base, struct commit *next,
 	return !clean;
 }
+static struct object_id *get_cache_tree_oid(void)
+{
+	if (!active_cache_tree)
+		active_cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(active_cache_tree))
+		if (cache_tree_update(&the_index, 0)) {
+			error(_("unable to update cache tree"));
+			return NULL;
+		}
+
+	return &active_cache_tree->oid;
+}
+
 static int is_index_unchanged(void)
 {
-	struct object_id head_oid;
+	struct object_id head_oid, *cache_tree_oid;
 	struct commit *head_commit;
 	if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
@@ -582,15 +603,10 @@ static int is_index_unchanged(void)
 	if (parse_commit(head_commit))
 		return -1;
-	if (!active_cache_tree)
-		active_cache_tree = cache_tree();
-
-	if (!cache_tree_fully_valid(active_cache_tree))
-		if (cache_tree_update(&the_index, 0))
-			return error(_("unable to update cache tree"));
-	return !oidcmp(&active_cache_tree->oid,
-		       get_commit_tree_oid(head_commit));
+	if (!(cache_tree_oid = get_cache_tree_oid()))
+		return -1;
+	return !oidcmp(cache_tree_oid, get_commit_tree_oid(head_commit));
 }
 static int write_author_script(const char *message)
@@ -682,6 +698,52 @@ static char *get_author(const char *message)
 	return NULL;
 }
+/* Read author-script and return an ident line (author <email> timestamp) */
+static const char *read_author_ident(struct strbuf *buf)
+{
+	const char *keys[] = {
+		"GIT_AUTHOR_NAME=", "GIT_AUTHOR_EMAIL=", "GIT_AUTHOR_DATE="
+	};
+	char *in, *out, *eol;
+	int i = 0, len;
+
+	if (strbuf_read_file(buf, rebase_path_author_script(), 256) <= 0)
+		return NULL;
+
+	/* dequote values and construct ident line in-place */
+	for (in = out = buf->buf; i < 3 && in - buf->buf < buf->len; i++) {
+		if (!skip_prefix(in, keys[i], (const char **)&in)) {
+			warning("could not parse '%s' (looking for '%s'",
+				rebase_path_author_script(), keys[i]);
+			return NULL;
+		}
+
+		eol = strchrnul(in, '\n');
+		*eol = '\0';
+		sq_dequote(in);
+		len = strlen(in);
+
+		if (i > 0) /* separate values by spaces */
+			*(out++) = ' ';
+		if (i == 1) /* email needs to be surrounded by <...> */
+			*(out++) = '<';
+		memmove(out, in, len);
+		out += len;
+		if (i == 1) /* email needs to be surrounded by <...> */
+			*(out++) = '>';
+		in = eol + 1;
+	}
+
+	if (i < 3) {
+		warning("could not parse '%s' (looking for '%s')",
+			rebase_path_author_script(), keys[i]);
+		return NULL;
+	}
+
+	buf->len = out - buf->buf;
+	return buf->buf;
+}
+
 static const char staged_changes_advice[] =
 N_("you have staged changes in your working tree\n"
 "If these changes are meant to be squashed into the previous commit, run:\n"
@@ -701,6 +763,7 @@ N_("you have staged changes in your working tree\n"
 #define AMEND_MSG   (1<<2)
 #define CLEANUP_MSG (1<<3)
 #define VERIFY_MSG  (1<<4)
+#define CREATE_ROOT_COMMIT (1<<5)
 /*
  * If we are cherry-pick, and if the merge did not result in
@@ -720,6 +783,40 @@ static int run_git_commit(const char *defmsg, struct replay_opts *opts,
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	const char *value;
+	if (flags & CREATE_ROOT_COMMIT) {
+		struct strbuf msg = STRBUF_INIT, script = STRBUF_INIT;
+		const char *author = is_rebase_i(opts) ?
+			read_author_ident(&script) : NULL;
+		struct object_id root_commit, *cache_tree_oid;
+		int res = 0;
+
+		if (!defmsg)
+			BUG("root commit without message");
+
+		if (!(cache_tree_oid = get_cache_tree_oid()))
+			res = -1;
+
+		if (!res)
+			res = strbuf_read_file(&msg, defmsg, 0);
+
+		if (res <= 0)
+			res = error_errno(_("could not read '%s'"), defmsg);
+		else
+			res = commit_tree(msg.buf, msg.len, cache_tree_oid,
+					  NULL, &root_commit, author,
+					  opts->gpg_sign);
+
+		strbuf_release(&msg);
+		strbuf_release(&script);
+		if (!res) {
+			update_ref(NULL, "CHERRY_PICK_HEAD", &root_commit, NULL,
+				   REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR);
+			res = update_ref(NULL, "HEAD", &root_commit, NULL, 0,
+					 UPDATE_REFS_MSG_ON_ERR);
+		}
+		return res < 0 ? error(_("writing root commit")) : 0;
+	}
+
 	cmd.git_cmd = 1;
 	if (is_rebase_i(opts)) {
@@ -1210,7 +1307,8 @@ static int do_commit(const char *msg_file, const char *author,
 {
 	int res = 1;
-	if (!(flags & EDIT_MSG) && !(flags & VERIFY_MSG)) {
+	if (!(flags & EDIT_MSG) && !(flags & VERIFY_MSG) &&
+	    !(flags & CREATE_ROOT_COMMIT)) {
 		struct object_id oid;
 		struct strbuf sb = STRBUF_INIT;
@@ -1363,6 +1461,22 @@ static int is_fixup(enum todo_command command)
 	return command == TODO_FIXUP || command == TODO_SQUASH;
 }
+/* Does this command create a (non-merge) commit? */
+static int is_pick_or_similar(enum todo_command command)
+{
+	switch (command) {
+	case TODO_PICK:
+	case TODO_REVERT:
+	case TODO_EDIT:
+	case TODO_REWORD:
+	case TODO_FIXUP:
+	case TODO_SQUASH:
+		return 1;
+	default:
+		return 0;
+	}
+}
+
 static int update_squash_messages(enum todo_command command,
 		struct commit *commit, struct replay_opts *opts)
 {
@@ -1516,7 +1630,14 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 			return error(_("your index file is unmerged."));
 	} else {
 		unborn = get_oid("HEAD", &head);
-		if (unborn)
+		/* Do we want to generate a root commit? */
+		if (is_pick_or_similar(command) && opts->have_squash_onto &&
+		    !oidcmp(&head, &opts->squash_onto)) {
+			if (is_fixup(command))
+				return error(_("cannot fixup root commit"));
+			flags |= CREATE_ROOT_COMMIT;
+			unborn = 1;
+		} else if (unborn)
 			oidcpy(&head, the_hash_algo->empty_tree);
 		if (index_differs_from(unborn ? EMPTY_TREE_SHA1_HEX : "HEAD",
 				       NULL, 0))
@@ -2142,6 +2263,12 @@ static int read_populate_opts(struct replay_opts *opts)
 			}
 		}
+		if (read_oneliner(&buf, rebase_path_squash_onto(), 0)) {
+			if (get_oid_hex(buf.buf, &opts->squash_onto) < 0)
+				return error(_("unusable squash-onto"));
+			opts->have_squash_onto = 1;
+		}
+
 		return 0;
 	}
@@ -2634,18 +2761,34 @@ 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));
@@ -2741,6 +2884,18 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
 		goto leave_merge;
 	}
+	if (opts->have_squash_onto &&
+	    !oidcmp(&head_commit->object.oid, &opts->squash_onto)) {
+		/*
+		 * When the user tells us to "merge" something into a
+		 * "[new root]", let's simply fast-forward to the merge head.
+		 */
+		rollback_lock_file(&lock);
+		ret = fast_forward_to(&merge_commit->object.oid,
+				       &head_commit->object.oid, 0, opts);
+		goto leave_merge;
+	}
+
 	if (commit) {
 		const char *message = get_commit_buffer(commit, NULL);
 		const char *body;
@@ -3850,7 +4005,8 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		}
 		if (!commit)
-			fprintf(out, "%s onto\n", cmd_reset);
+			fprintf(out, "%s %s\n", cmd_reset,
+				rebase_cousins ? "onto" : "[new root]");
 		else {
 			const char *to = NULL;

sequencer.h

@@ -48,6 +48,10 @@ struct replay_opts {
 	struct strbuf current_fixups;
 	int current_fixup_count;
+	/* placeholder commit for -i --root */
+	struct object_id squash_onto;
+	int have_squash_onto;
+
 	/* Only used by REPLAY_NONE */
 	struct rev_info *revs;
 };

t/t3404-rebase-interactive.sh

@@ -1204,10 +1204,6 @@ test_expect_success 'drop' '
 	test A = $(git cat-file commit HEAD^^ | sed -ne \$p)
 '
-cat >expect <<EOF
-Successfully rebased and updated refs/heads/missing-commit.
-EOF
-
 test_expect_success 'rebase -i respects rebase.missingCommitsCheck = ignore' '
 	test_config rebase.missingCommitsCheck ignore &&
 	rebase_setup_and_clean missing-commit &&
@@ -1215,7 +1211,9 @@ test_expect_success 'rebase -i respects rebase.missingCommitsCheck = ignore' '
 	FAKE_LINES="1 2 3 4" \
 		git rebase -i --root 2>actual &&
 	test D = $(git cat-file commit HEAD | sed -ne \$p) &&
-	test_i18ncmp expect actual
+	test_i18ngrep \
+		"Successfully rebased and updated refs/heads/missing-commit" \
+		actual
 '
 cat >expect <<EOF
@@ -1227,15 +1225,24 @@ To avoid this message, use "drop" to explicitly remove a commit.
 Use 'git config rebase.missingCommitsCheck' to change the level of warnings.
 The possible behaviours are: ignore, warn, error.
+Rebasing (1/4)
+Rebasing (2/4)
+Rebasing (3/4)
+Rebasing (4/4)
 Successfully rebased and updated refs/heads/missing-commit.
 EOF
+cr_to_nl () {
+	tr '\015' '\012'
+}
+
 test_expect_success 'rebase -i respects rebase.missingCommitsCheck = warn' '
 	test_config rebase.missingCommitsCheck warn &&
 	rebase_setup_and_clean missing-commit &&
 	set_fake_editor &&
 	FAKE_LINES="1 2 3 4" \
-		git rebase -i --root 2>actual &&
+		git rebase -i --root 2>actual.2 &&
+	cr_to_nl <actual.2 >actual &&
 	test_i18ncmp expect actual &&
 	test D = $(git cat-file commit HEAD | sed -ne \$p)
 '

t/t3421-rebase-topology-linear.sh

@@ -328,9 +328,9 @@ test_run_rebase () {
 		test_cmp_rev c HEAD
 	"
 }
-test_run_rebase failure ''
-test_run_rebase failure -m
-test_run_rebase failure -i
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
 test_run_rebase failure -p
 test_run_rebase () {

t/t3430-rebase-merges.sh

@@ -241,4 +241,76 @@ 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 $before
+'
+
+test_expect_success 'a "merge" into a root commit is a fast-forward' '
+	head=$(git rev-parse HEAD) &&
+	cat >script-from-scratch <<-EOF &&
+	reset [new root]
+	merge $head
+	EOF
+	test_config sequence.editor \""$PWD"/replace-editor.sh\" &&
+	test_tick &&
+	git rebase -i -r HEAD^ &&
+	test_cmp_rev HEAD $head
+'
+
+test_expect_success 'A root commit can be a cousin, treat it that way' '
+	git checkout --orphan khnum &&
+	test_commit yama &&
+	git checkout -b asherah master &&
+	test_commit shamkat &&
+	git merge --allow-unrelated-histories khnum &&
+	test_tick &&
+	git rebase -f -r HEAD^ &&
+	! test_cmp_rev HEAD^2 khnum &&
+	test_cmp_graph HEAD^.. <<-\EOF &&
+	*   Merge branch '\''khnum'\'' into asherah
+	|\
+	| * yama
+	o shamkat
+	EOF
+	test_tick &&
+	git rebase --rebase-merges=rebase-cousins HEAD^ &&
+	test_cmp_graph HEAD^.. <<-\EOF
+	*   Merge branch '\''khnum'\'' into asherah
+	|\
+	| * yama
+	|/
+	o shamkat
+	EOF
+'
+
 test_done