[PATCH v8 06/16] sequencer: introduce the `merge` command

[Johannes Schindelin <johannes.schindelin@gmx.de>]

This patch is part of the effort to reimplement `--preserve-merges` with
a substantially improved design, a design that has been developed in the
Git for Windows project to maintain the dozens of Windows-specific patch
series on top of upstream Git.

The previous patch implemented the `label` and `reset` commands to label
commits and to reset to labeled commits. This patch adds the `merge`
command, with the following syntax:

	merge [-C <commit>] <rev> # <oneline>

The <commit> parameter in this instance is the *original* merge commit,
whose author and message will be used for the merge commit that is about
to be created.

The <rev> parameter refers to the (possibly rewritten) revision to
merge. Let's see an example of a todo list:

	label onto

	# Branch abc
	reset onto
	pick deadbeef Hello, world!
	label abc

	reset onto
	pick cafecafe And now for something completely different
	merge -C baaabaaa abc # Merge the branch 'abc' into master

To edit the merge commit's message (a "reword" for merges, if you will),
use `-c` (lower-case) instead of `-C`; this convention was borrowed from
`git commit` that also supports `-c` and `-C` with similar meanings.

To create *new* merges, i.e. without copying the commit message from an
existing commit, simply omit the `-C <commit>` parameter (which will
open an editor for the merge message):

	merge abc

This comes in handy when splitting a branch into two or more branches.

Note: this patch only adds support for recursive merges, to keep things
simple. Support for octopus merges will be added later in a separate
patch series, support for merges using strategies other than the
recursive merge is left for the future.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 git-rebase--interactive.sh |   6 +
 sequencer.c                | 407 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 406 insertions(+), 7 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index e1b865f43f2..ccd5254d1c9 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -162,6 +162,12 @@ s, squash <commit> = use commit, but meld into previous commit
 f, fixup <commit> = like \"squash\", but discard this commit's log message
 x, exec <commit> = run command (the rest of the line) using shell
 d, drop <commit> = remove commit
+l, label <label> = label current HEAD with a name
+t, reset <label> = reset HEAD to a label
+m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
+.       create a merge commit using the original merge commit's
+.       message (or the oneline, if no original merge commit was
+.       specified). Use -c <commit> to reword the commit message.
 
 These lines can be re-ordered; they are executed from top to bottom.
 " | git stripspace --comment-lines >>"$todo"
diff --git a/sequencer.c b/sequencer.c
index 01443e0f245..35fcacbdf0f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -23,6 +23,8 @@
 #include "hashmap.h"
 #include "notes-utils.h"
 #include "sigchain.h"
+#include "unpack-trees.h"
+#include "worktree.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
@@ -120,6 +122,13 @@ static GIT_PATH_FUNC(rebase_path_stopped_sha, "rebase-merge/stopped-sha")
 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 listing refs that need to be deleted after the rebase
+ * finishes. This is used by the `label` command to record the need for cleanup.
+ */
+static GIT_PATH_FUNC(rebase_path_refs_to_delete, "rebase-merge/refs-to-delete")
+
 /*
  * The following files are written by git-rebase just after parsing the
  * command-line (and are only consumed, not modified, by the sequencer).
@@ -244,18 +253,34 @@ static const char *gpg_sign_opt_quoted(struct replay_opts *opts)
 
 int sequencer_remove_state(struct replay_opts *opts)
 {
-	struct strbuf dir = STRBUF_INIT;
+	struct strbuf buf = STRBUF_INIT;
 	int i;
 
+	if (is_rebase_i(opts) &&
+	    strbuf_read_file(&buf, rebase_path_refs_to_delete(), 0) > 0) {
+		char *p = buf.buf;
+		while (*p) {
+			char *eol = strchr(p, '\n');
+			if (eol)
+				*eol = '\0';
+			if (delete_ref("(rebase -i) cleanup", p, NULL, 0) < 0)
+				warning(_("could not delete '%s'"), p);
+			if (!eol)
+				break;
+			p = eol + 1;
+		}
+	}
+
 	free(opts->gpg_sign);
 	free(opts->strategy);
 	for (i = 0; i < opts->xopts_nr; i++)
 		free(opts->xopts[i]);
 	free(opts->xopts);
 
-	strbuf_addstr(&dir, get_dir(opts));
-	remove_dir_recursively(&dir, 0);
-	strbuf_release(&dir);
+	strbuf_reset(&buf);
+	strbuf_addstr(&buf, get_dir(opts));
+	remove_dir_recursively(&buf, 0);
+	strbuf_release(&buf);
 
 	return 0;
 }
@@ -1279,6 +1304,9 @@ enum todo_command {
 	TODO_SQUASH,
 	/* commands that do something else than handling a single commit */
 	TODO_EXEC,
+	TODO_LABEL,
+	TODO_RESET,
+	TODO_MERGE,
 	/* commands that do nothing but are counted for reporting progress */
 	TODO_NOOP,
 	TODO_DROP,
@@ -1297,6 +1325,9 @@ static struct {
 	{ 'f', "fixup" },
 	{ 's', "squash" },
 	{ 'x', "exec" },
+	{ 'l', "label" },
+	{ 't', "reset" },
+	{ 'm', "merge" },
 	{ 0,   "noop" },
 	{ 'd', "drop" },
 	{ 0,   NULL }
@@ -1724,9 +1755,14 @@ static int read_and_refresh_cache(struct replay_opts *opts)
 	return 0;
 }
 
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG = 1
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
+	unsigned int flags;
 	const char *arg;
 	int arg_len;
 	size_t offset_in_buf;
@@ -1761,6 +1797,8 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 	char *end_of_object_name;
 	int i, saved, status, padding;
 
+	item->flags = 0;
+
 	/* left-trim */
 	bol += strspn(bol, " \t");
 
@@ -1802,13 +1840,29 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 		return error(_("missing arguments for %s"),
 			     command_to_string(item->command));
 
-	if (item->command == TODO_EXEC) {
+	if (item->command == TODO_EXEC || item->command == TODO_LABEL ||
+	    item->command == TODO_RESET) {
 		item->commit = NULL;
 		item->arg = bol;
 		item->arg_len = (int)(eol - bol);
 		return 0;
 	}
 
+	if (item->command == TODO_MERGE) {
+		if (skip_prefix(bol, "-C", &bol))
+			bol += strspn(bol, " \t");
+		else if (skip_prefix(bol, "-c", &bol)) {
+			bol += strspn(bol, " \t");
+			item->flags |= TODO_EDIT_MERGE_MSG;
+		} else {
+			item->flags |= TODO_EDIT_MERGE_MSG;
+			item->commit = NULL;
+			item->arg = bol;
+			item->arg_len = (int)(eol - bol);
+			return 0;
+		}
+	}
+
 	end_of_object_name = (char *) bol + strcspn(bol, " \t\n");
 	saved = *end_of_object_name;
 	*end_of_object_name = '\0';
@@ -2465,6 +2519,305 @@ static int do_exec(const char *command_line)
 	return status;
 }
 
+static int safe_append(const char *filename, const char *fmt, ...)
+{
+	va_list ap;
+	struct lock_file lock = LOCK_INIT;
+	int fd = hold_lock_file_for_update(&lock, filename,
+					   LOCK_REPORT_ON_ERROR);
+	struct strbuf buf = STRBUF_INIT;
+
+	if (fd < 0)
+		return -1;
+
+	if (strbuf_read_file(&buf, filename, 0) < 0 && errno != ENOENT) {
+		error_errno(_("could not read '%s'"), filename);
+		rollback_lock_file(&lock);
+		return -1;
+	}
+	strbuf_complete(&buf, '\n');
+	va_start(ap, fmt);
+	strbuf_vaddf(&buf, fmt, ap);
+	va_end(ap);
+
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
+		error_errno(_("could not write to '%s'"), filename);
+		strbuf_release(&buf);
+		rollback_lock_file(&lock);
+		return -1;
+	}
+	if (commit_lock_file(&lock) < 0) {
+		strbuf_release(&buf);
+		rollback_lock_file(&lock);
+		return error(_("failed to finalize '%s'"), filename);
+	}
+
+	strbuf_release(&buf);
+	return 0;
+}
+
+static int do_label(const char *name, int len)
+{
+	struct ref_store *refs = get_main_ref_store();
+	struct ref_transaction *transaction;
+	struct strbuf ref_name = STRBUF_INIT, err = STRBUF_INIT;
+	struct strbuf msg = STRBUF_INIT;
+	int ret = 0;
+	struct object_id head_oid;
+
+	if (len == 1 && *name == '#')
+		return error("Illegal label name: '%.*s'", len, name);
+
+	strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
+	strbuf_addf(&msg, "rebase -i (label) '%.*s'", len, name);
+
+	transaction = ref_store_transaction_begin(refs, &err);
+	if (!transaction) {
+		error("%s", err.buf);
+		ret = -1;
+	} else if (get_oid("HEAD", &head_oid)) {
+		error(_("could not read HEAD"));
+		ret = -1;
+	} else if (ref_transaction_update(transaction, ref_name.buf, &head_oid,
+					  NULL, 0, msg.buf, &err) < 0 ||
+		   ref_transaction_commit(transaction, &err)) {
+		error("%s", err.buf);
+		ret = -1;
+	}
+	ref_transaction_free(transaction);
+	strbuf_release(&err);
+	strbuf_release(&msg);
+
+	if (!ret)
+		ret = safe_append(rebase_path_refs_to_delete(),
+				  "%s\n", ref_name.buf);
+	strbuf_release(&ref_name);
+
+	return ret;
+}
+
+static const char *reflog_message(struct replay_opts *opts,
+	const char *sub_action, const char *fmt, ...);
+
+static int do_reset(const char *name, int len, struct replay_opts *opts)
+{
+	struct strbuf ref_name = STRBUF_INIT;
+	struct object_id oid;
+	struct lock_file lock = LOCK_INIT;
+	struct tree_desc desc;
+	struct tree *tree;
+	struct unpack_trees_options unpack_tree_opts;
+	int ret = 0, i;
+
+	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;
+	}
+
+	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
+	unpack_tree_opts.head_idx = 1;
+	unpack_tree_opts.src_index = &the_index;
+	unpack_tree_opts.dst_index = &the_index;
+	unpack_tree_opts.fn = oneway_merge;
+	unpack_tree_opts.merge = 1;
+	unpack_tree_opts.update = 1;
+
+	if (read_cache_unmerged()) {
+		rollback_lock_file(&lock);
+		strbuf_release(&ref_name);
+		return error_resolve_conflict(_(action_name(opts)));
+	}
+
+	if (!fill_tree_descriptor(&desc, &oid)) {
+		error(_("failed to find tree of %s"), oid_to_hex(&oid));
+		rollback_lock_file(&lock);
+		free((void *)desc.buffer);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	if (unpack_trees(1, &desc, &unpack_tree_opts)) {
+		rollback_lock_file(&lock);
+		free((void *)desc.buffer);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	tree = parse_tree_indirect(&oid);
+	prime_cache_tree(&the_index, tree);
+
+	if (write_locked_index(&the_index, &lock, COMMIT_LOCK) < 0)
+		ret = error(_("could not write index"));
+	free((void *)desc.buffer);
+
+	if (!ret)
+		ret = update_ref(reflog_message(opts, "reset", "'%.*s'",
+						len, name), "HEAD", &oid,
+				 NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+
+	strbuf_release(&ref_name);
+	return ret;
+}
+
+static int do_merge(struct commit *commit, const char *arg, int arg_len,
+		    int flags, struct replay_opts *opts)
+{
+	int run_commit_flags = (flags & TODO_EDIT_MERGE_MSG) ?
+		EDIT_MSG | VERIFY_MSG : 0;
+	struct strbuf ref_name = STRBUF_INIT;
+	struct commit *head_commit, *merge_commit, *i;
+	struct commit_list *bases, *j, *reversed = NULL;
+	struct merge_options o;
+	int merge_arg_len, oneline_offset, ret;
+	static struct lock_file lock;
+	const char *p;
+
+	if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0) {
+		ret = -1;
+		goto leave_merge;
+	}
+
+	head_commit = lookup_commit_reference_by_name("HEAD");
+	if (!head_commit) {
+		ret = error(_("cannot merge without a current revision"));
+		goto leave_merge;
+	}
+
+	oneline_offset = arg_len;
+	merge_arg_len = strcspn(arg, " \t\n");
+	p = arg + merge_arg_len;
+	p += strspn(p, " \t\n");
+	if (*p == '#' && (!p[1] || isspace(p[1]))) {
+		p += 1 + strspn(p + 1, " \t\n");
+		oneline_offset = p - arg;
+	} else if (p - arg < arg_len)
+		BUG("octopus merges are not supported yet: '%s'", p);
+
+	strbuf_addf(&ref_name, "refs/rewritten/%.*s", merge_arg_len, arg);
+	merge_commit = lookup_commit_reference_by_name(ref_name.buf);
+	if (!merge_commit) {
+		/* fall back to non-rewritten ref or commit */
+		strbuf_splice(&ref_name, 0, strlen("refs/rewritten/"), "", 0);
+		merge_commit = lookup_commit_reference_by_name(ref_name.buf);
+	}
+
+	if (!merge_commit) {
+		ret = error(_("could not resolve '%s'"), ref_name.buf);
+		goto leave_merge;
+	}
+
+	if (commit) {
+		const char *message = get_commit_buffer(commit, NULL);
+		const char *body;
+		int len;
+
+		if (!message) {
+			ret = error(_("could not get commit message of '%s'"),
+				    oid_to_hex(&commit->object.oid));
+			goto leave_merge;
+		}
+		write_author_script(message);
+		find_commit_subject(message, &body);
+		len = strlen(body);
+		ret = write_message(body, len, git_path_merge_msg(), 0);
+		unuse_commit_buffer(commit, message);
+		if (ret) {
+			error_errno(_("could not write '%s'"),
+				    git_path_merge_msg());
+			goto leave_merge;
+		}
+	} else {
+		struct strbuf buf = STRBUF_INIT;
+		int len;
+
+		strbuf_addf(&buf, "author %s", git_author_info(0));
+		write_author_script(buf.buf);
+		strbuf_reset(&buf);
+
+		if (oneline_offset < arg_len) {
+			p = arg + oneline_offset;
+			len = arg_len - oneline_offset;
+		} else {
+			strbuf_addf(&buf, "Merge branch '%.*s'",
+				    merge_arg_len, arg);
+			p = buf.buf;
+			len = buf.len;
+		}
+
+		ret = write_message(p, len, git_path_merge_msg(), 0);
+		strbuf_release(&buf);
+		if (ret) {
+			error_errno(_("could not write '%s'"),
+				    git_path_merge_msg());
+			goto leave_merge;
+		}
+	}
+
+	write_message(oid_to_hex(&merge_commit->object.oid), GIT_SHA1_HEXSZ,
+		      git_path_merge_head(), 0);
+	write_message("no-ff", 5, git_path_merge_mode(), 0);
+
+	bases = get_merge_bases(head_commit, merge_commit);
+	for (j = bases; j; j = j->next)
+		commit_list_insert(j->item, &reversed);
+	free_commit_list(bases);
+
+	read_cache();
+	init_merge_options(&o);
+	o.branch1 = "HEAD";
+	o.branch2 = ref_name.buf;
+	o.buffer_output = 2;
+
+	ret = merge_recursive(&o, head_commit, merge_commit, reversed, &i);
+	if (ret <= 0)
+		fputs(o.obuf.buf, stdout);
+	strbuf_release(&o.obuf);
+	if (ret < 0) {
+		error(_("could not even attempt to merge '%.*s'"),
+		      merge_arg_len, arg);
+		goto leave_merge;
+	}
+	/*
+	 * The return value of merge_recursive() is 1 on clean, and 0 on
+	 * unclean merge.
+	 *
+	 * Let's reverse that, so that do_merge() returns 0 upon success and
+	 * 1 upon failed merge (keeping the return value -1 for the cases where
+	 * we will want to reschedule the `merge` command).
+	 */
+	ret = !ret;
+
+	if (active_cache_changed &&
+	    write_locked_index(&the_index, &lock, COMMIT_LOCK)) {
+		ret = error(_("merge: Unable to write new index file"));
+		goto leave_merge;
+	}
+
+	rollback_lock_file(&lock);
+	if (ret)
+		rerere(opts->allow_rerere_auto);
+	else
+		ret = run_git_commit(git_path_merge_msg(), opts,
+				     run_commit_flags);
+
+leave_merge:
+	strbuf_release(&ref_name);
+	rollback_lock_file(&lock);
+	return ret;
+}
+
 static int is_final_fixup(struct todo_list *todo_list)
 {
 	int i = todo_list->current;
@@ -2568,7 +2921,7 @@ N_("Could not execute the todo command\n"
 
 static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 {
-	int res = 0;
+	int res = 0, reschedule = 0;
 
 	setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
 	if (opts->allow_ff)
@@ -2639,7 +2992,7 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 					intend_to_amend();
 				return error_failed_squash(item->commit, opts,
 					item->arg_len, item->arg);
-			} else if (res && is_rebase_i(opts))
+			} else if (res && is_rebase_i(opts) && item->commit)
 				return res | error_with_patch(item->commit,
 					item->arg, item->arg_len, opts, res,
 					item->command == TODO_REWORD);
@@ -2665,9 +3018,41 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 				/* `current` will be incremented below */
 				todo_list->current = -1;
 			}
+		} else if (item->command == TODO_LABEL) {
+			if ((res = do_label(item->arg, item->arg_len)))
+				reschedule = 1;
+		} else if (item->command == TODO_RESET) {
+			if ((res = do_reset(item->arg, item->arg_len, opts)))
+				reschedule = 1;
+		} else if (item->command == TODO_MERGE) {
+			if ((res = do_merge(item->commit,
+					    item->arg, item->arg_len,
+					    item->flags, opts)) < 0)
+				reschedule = 1;
+			else if (res > 0)
+				/* failed with merge conflicts */
+				return error_with_patch(item->commit,
+							item->arg,
+							item->arg_len, opts,
+							res, 0);
 		} else if (!is_noop(item->command))
 			return error(_("unknown command %d"), item->command);
 
+		if (reschedule) {
+			advise(_(rescheduled_advice),
+			       get_item_line_length(todo_list,
+						    todo_list->current),
+			       get_item_line(todo_list, todo_list->current));
+			todo_list->current--;
+			if (save_todo(todo_list, opts))
+				return -1;
+			if (item->commit)
+				return error_with_patch(item->commit,
+							item->arg,
+							item->arg_len, opts,
+							res, 0);
+		}
+
 		todo_list->current++;
 		if (res)
 			return res;
@@ -3147,8 +3532,16 @@ int transform_todos(unsigned flags)
 					  short_commit_name(item->commit) :
 					  oid_to_hex(&item->commit->object.oid);
 
+			if (item->command == TODO_MERGE) {
+				if (item->flags & TODO_EDIT_MERGE_MSG)
+					strbuf_addstr(&buf, " -c");
+				else
+					strbuf_addstr(&buf, " -C");
+			}
+
 			strbuf_addf(&buf, " %s", oid);
 		}
+
 		/* add all the rest */
 		if (!item->arg_len)
 			strbuf_addch(&buf, '\n');
-- 
2.17.0.windows.1.15.gaa56ade3205