merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

1 files changed, 1680 insertions, 0 deletions

diff --git a/third_party/git/builtin/merge.c b/third_party/git/builtin/merge.c
new file mode 100644
index 0000000000..e2ccbc44e2
--- /dev/null
+++ b/third_party/git/builtin/merge.c
@@ -0,0 +1,1680 @@
+/*
+ * Builtin "git merge"
+ *
+ * Copyright (c) 2008 Miklos Vajna <vmiklos@frugalware.org>
+ *
+ * Based on git-merge.sh by Junio C Hamano.
+ */
+
+#define USE_THE_INDEX_COMPATIBILITY_MACROS
+#include "cache.h"
+#include "config.h"
+#include "parse-options.h"
+#include "builtin.h"
+#include "lockfile.h"
+#include "run-command.h"
+#include "diff.h"
+#include "refs.h"
+#include "refspec.h"
+#include "commit.h"
+#include "diffcore.h"
+#include "revision.h"
+#include "unpack-trees.h"
+#include "cache-tree.h"
+#include "dir.h"
+#include "utf8.h"
+#include "log-tree.h"
+#include "color.h"
+#include "rerere.h"
+#include "help.h"
+#include "merge-recursive.h"
+#include "resolve-undo.h"
+#include "remote.h"
+#include "fmt-merge-msg.h"
+#include "gpg-interface.h"
+#include "sequencer.h"
+#include "string-list.h"
+#include "packfile.h"
+#include "tag.h"
+#include "alias.h"
+#include "branch.h"
+#include "commit-reach.h"
+#include "wt-status.h"
+
+#define DEFAULT_TWOHEAD (1<<0)
+#define DEFAULT_OCTOPUS (1<<1)
+#define NO_FAST_FORWARD (1<<2)
+#define NO_TRIVIAL      (1<<3)
+
+struct strategy {
+	const char *name;
+	unsigned attr;
+};
+
+static const char * const builtin_merge_usage[] = {
+	N_("git merge [<options>] [<commit>...]"),
+	N_("git merge --abort"),
+	N_("git merge --continue"),
+	NULL
+};
+
+static int show_diffstat = 1, shortlog_len = -1, squash;
+static int option_commit = -1;
+static int option_edit = -1;
+static int allow_trivial = 1, have_message, verify_signatures;
+static int overwrite_ignore = 1;
+static struct strbuf merge_msg = STRBUF_INIT;
+static struct strategy **use_strategies;
+static size_t use_strategies_nr, use_strategies_alloc;
+static const char **xopts;
+static size_t xopts_nr, xopts_alloc;
+static const char *branch;
+static char *branch_mergeoptions;
+static int option_renormalize;
+static int verbosity;
+static int allow_rerere_auto;
+static int abort_current_merge;
+static int quit_current_merge;
+static int continue_current_merge;
+static int allow_unrelated_histories;
+static int show_progress = -1;
+static int default_to_upstream = 1;
+static int signoff;
+static const char *sign_commit;
+static int verify_msg = 1;
+
+static struct strategy all_strategy[] = {
+	{ "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
+	{ "octopus",    DEFAULT_OCTOPUS },
+	{ "resolve",    0 },
+	{ "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
+	{ "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
+};
+
+static const char *pull_twohead, *pull_octopus;
+
+enum ff_type {
+	FF_NO,
+	FF_ALLOW,
+	FF_ONLY
+};
+
+static enum ff_type fast_forward = FF_ALLOW;
+
+static const char *cleanup_arg;
+static enum commit_msg_cleanup_mode cleanup_mode;
+
+static int option_parse_message(const struct option *opt,
+				const char *arg, int unset)
+{
+	struct strbuf *buf = opt->value;
+
+	if (unset)
+		strbuf_setlen(buf, 0);
+	else if (arg) {
+		strbuf_addf(buf, "%s%s", buf->len ? "\n\n" : "", arg);
+		have_message = 1;
+	} else
+		return error(_("switch `m' requires a value"));
+	return 0;
+}
+
+static enum parse_opt_result option_read_message(struct parse_opt_ctx_t *ctx,
+						 const struct option *opt,
+						 const char *arg_not_used,
+						 int unset)
+{
+	struct strbuf *buf = opt->value;
+	const char *arg;
+
+	BUG_ON_OPT_ARG(arg_not_used);
+	if (unset)
+		BUG("-F cannot be negated");
+
+	if (ctx->opt) {
+		arg = ctx->opt;
+		ctx->opt = NULL;
+	} else if (ctx->argc > 1) {
+		ctx->argc--;
+		arg = *++ctx->argv;
+	} else
+		return error(_("option `%s' requires a value"), opt->long_name);
+
+	if (buf->len)
+		strbuf_addch(buf, '\n');
+	if (ctx->prefix && !is_absolute_path(arg))
+		arg = prefix_filename(ctx->prefix, arg);
+	if (strbuf_read_file(buf, arg, 0) < 0)
+		return error(_("could not read file '%s'"), arg);
+	have_message = 1;
+
+	return 0;
+}
+
+static struct strategy *get_strategy(const char *name)
+{
+	int i;
+	struct strategy *ret;
+	static struct cmdnames main_cmds, other_cmds;
+	static int loaded;
+
+	if (!name)
+		return NULL;
+
+	for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
+		if (!strcmp(name, all_strategy[i].name))
+			return &all_strategy[i];
+
+	if (!loaded) {
+		struct cmdnames not_strategies;
+		loaded = 1;
+
+		memset(&not_strategies, 0, sizeof(struct cmdnames));
+		load_command_list("git-merge-", &main_cmds, &other_cmds);
+		for (i = 0; i < main_cmds.cnt; i++) {
+			int j, found = 0;
+			struct cmdname *ent = main_cmds.names[i];
+			for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
+				if (!strncmp(ent->name, all_strategy[j].name, ent->len)
+						&& !all_strategy[j].name[ent->len])
+					found = 1;
+			if (!found)
+				add_cmdname(&not_strategies, ent->name, ent->len);
+		}
+		exclude_cmds(&main_cmds, &not_strategies);
+	}
+	if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
+		fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
+		fprintf(stderr, _("Available strategies are:"));
+		for (i = 0; i < main_cmds.cnt; i++)
+			fprintf(stderr, " %s", main_cmds.names[i]->name);
+		fprintf(stderr, ".\n");
+		if (other_cmds.cnt) {
+			fprintf(stderr, _("Available custom strategies are:"));
+			for (i = 0; i < other_cmds.cnt; i++)
+				fprintf(stderr, " %s", other_cmds.names[i]->name);
+			fprintf(stderr, ".\n");
+		}
+		exit(1);
+	}
+
+	ret = xcalloc(1, sizeof(struct strategy));
+	ret->name = xstrdup(name);
+	ret->attr = NO_TRIVIAL;
+	return ret;
+}
+
+static void append_strategy(struct strategy *s)
+{
+	ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
+	use_strategies[use_strategies_nr++] = s;
+}
+
+static int option_parse_strategy(const struct option *opt,
+				 const char *name, int unset)
+{
+	if (unset)
+		return 0;
+
+	append_strategy(get_strategy(name));
+	return 0;
+}
+
+static int option_parse_x(const struct option *opt,
+			  const char *arg, int unset)
+{
+	if (unset)
+		return 0;
+
+	ALLOC_GROW(xopts, xopts_nr + 1, xopts_alloc);
+	xopts[xopts_nr++] = xstrdup(arg);
+	return 0;
+}
+
+static int option_parse_n(const struct option *opt,
+			  const char *arg, int unset)
+{
+	BUG_ON_OPT_ARG(arg);
+	show_diffstat = unset;
+	return 0;
+}
+
+static struct option builtin_merge_options[] = {
+	{ OPTION_CALLBACK, 'n', NULL, NULL, NULL,
+		N_("do not show a diffstat at the end of the merge"),
+		PARSE_OPT_NOARG, option_parse_n },
+	OPT_BOOL(0, "stat", &show_diffstat,
+		N_("show a diffstat at the end of the merge")),
+	OPT_BOOL(0, "summary", &show_diffstat, N_("(synonym to --stat)")),
+	{ OPTION_INTEGER, 0, "log", &shortlog_len, N_("n"),
+	  N_("add (at most <n>) entries from shortlog to merge commit message"),
+	  PARSE_OPT_OPTARG, NULL, DEFAULT_MERGE_LOG_LEN },
+	OPT_BOOL(0, "squash", &squash,
+		N_("create a single commit instead of doing a merge")),
+	OPT_BOOL(0, "commit", &option_commit,
+		N_("perform a commit if the merge succeeds (default)")),
+	OPT_BOOL('e', "edit", &option_edit,
+		N_("edit message before committing")),
+	OPT_CLEANUP(&cleanup_arg),
+	OPT_SET_INT(0, "ff", &fast_forward, N_("allow fast-forward (default)"), FF_ALLOW),
+	OPT_SET_INT_F(0, "ff-only", &fast_forward,
+		      N_("abort if fast-forward is not possible"),
+		      FF_ONLY, PARSE_OPT_NONEG),
+	OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
+	OPT_BOOL(0, "verify-signatures", &verify_signatures,
+		N_("verify that the named commit has a valid GPG signature")),
+	OPT_CALLBACK('s', "strategy", &use_strategies, N_("strategy"),
+		N_("merge strategy to use"), option_parse_strategy),
+	OPT_CALLBACK('X', "strategy-option", &xopts, N_("option=value"),
+		N_("option for selected merge strategy"), option_parse_x),
+	OPT_CALLBACK('m', "message", &merge_msg, N_("message"),
+		N_("merge commit message (for a non-fast-forward merge)"),
+		option_parse_message),
+	{ OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
+		N_("read message from file"), PARSE_OPT_NONEG,
+		NULL, 0, option_read_message },
+	OPT__VERBOSITY(&verbosity),
+	OPT_BOOL(0, "abort", &abort_current_merge,
+		N_("abort the current in-progress merge")),
+	OPT_BOOL(0, "quit", &quit_current_merge,
+		N_("--abort but leave index and working tree alone")),
+	OPT_BOOL(0, "continue", &continue_current_merge,
+		N_("continue the current in-progress merge")),
+	OPT_BOOL(0, "allow-unrelated-histories", &allow_unrelated_histories,
+		 N_("allow merging unrelated histories")),
+	OPT_SET_INT(0, "progress", &show_progress, N_("force progress reporting"), 1),
+	{ OPTION_STRING, 'S', "gpg-sign", &sign_commit, N_("key-id"),
+	  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
+	OPT_BOOL(0, "overwrite-ignore", &overwrite_ignore, N_("update ignored files (default)")),
+	OPT_BOOL(0, "signoff", &signoff, N_("add Signed-off-by:")),
+	OPT_BOOL(0, "verify", &verify_msg, N_("verify commit-msg hook")),
+	OPT_END()
+};
+
+static int save_state(struct object_id *stash)
+{
+	int len;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf buffer = STRBUF_INIT;
+	const char *argv[] = {"stash", "create", NULL};
+	int rc = -1;
+
+	cp.argv = argv;
+	cp.out = -1;
+	cp.git_cmd = 1;
+
+	if (start_command(&cp))
+		die(_("could not run stash."));
+	len = strbuf_read(&buffer, cp.out, 1024);
+	close(cp.out);
+
+	if (finish_command(&cp) || len < 0)
+		die(_("stash failed"));
+	else if (!len)		/* no changes */
+		goto out;
+	strbuf_setlen(&buffer, buffer.len-1);
+	if (get_oid(buffer.buf, stash))
+		die(_("not a valid object: %s"), buffer.buf);
+	rc = 0;
+out:
+	strbuf_release(&buffer);
+	return rc;
+}
+
+static void read_empty(const struct object_id *oid, int verbose)
+{
+	int i = 0;
+	const char *args[7];
+
+	args[i++] = "read-tree";
+	if (verbose)
+		args[i++] = "-v";
+	args[i++] = "-m";
+	args[i++] = "-u";
+	args[i++] = empty_tree_oid_hex();
+	args[i++] = oid_to_hex(oid);
+	args[i] = NULL;
+
+	if (run_command_v_opt(args, RUN_GIT_CMD))
+		die(_("read-tree failed"));
+}
+
+static void reset_hard(const struct object_id *oid, int verbose)
+{
+	int i = 0;
+	const char *args[6];
+
+	args[i++] = "read-tree";
+	if (verbose)
+		args[i++] = "-v";
+	args[i++] = "--reset";
+	args[i++] = "-u";
+	args[i++] = oid_to_hex(oid);
+	args[i] = NULL;
+
+	if (run_command_v_opt(args, RUN_GIT_CMD))
+		die(_("read-tree failed"));
+}
+
+static void restore_state(const struct object_id *head,
+			  const struct object_id *stash)
+{
+	struct strbuf sb = STRBUF_INIT;
+	const char *args[] = { "stash", "apply", NULL, NULL };
+
+	if (is_null_oid(stash))
+		return;
+
+	reset_hard(head, 1);
+
+	args[2] = oid_to_hex(stash);
+
+	/*
+	 * It is OK to ignore error here, for example when there was
+	 * nothing to restore.
+	 */
+	run_command_v_opt(args, RUN_GIT_CMD);
+
+	strbuf_release(&sb);
+	refresh_cache(REFRESH_QUIET);
+}
+
+/* This is called when no merge was necessary. */
+static void finish_up_to_date(const char *msg)
+{
+	if (verbosity >= 0)
+		printf("%s%s\n", squash ? _(" (nothing to squash)") : "", msg);
+	remove_merge_branch_state(the_repository);
+}
+
+static void squash_message(struct commit *commit, struct commit_list *remoteheads)
+{
+	struct rev_info rev;
+	struct strbuf out = STRBUF_INIT;
+	struct commit_list *j;
+	struct pretty_print_context ctx = {0};
+
+	printf(_("Squash commit -- not updating HEAD\n"));
+
+	repo_init_revisions(the_repository, &rev, NULL);
+	rev.ignore_merges = 1;
+	rev.commit_format = CMIT_FMT_MEDIUM;
+
+	commit->object.flags |= UNINTERESTING;
+	add_pending_object(&rev, &commit->object, NULL);
+
+	for (j = remoteheads; j; j = j->next)
+		add_pending_object(&rev, &j->item->object, NULL);
+
+	setup_revisions(0, NULL, &rev, NULL);
+	if (prepare_revision_walk(&rev))
+		die(_("revision walk setup failed"));
+
+	ctx.abbrev = rev.abbrev;
+	ctx.date_mode = rev.date_mode;
+	ctx.fmt = rev.commit_format;
+
+	strbuf_addstr(&out, "Squashed commit of the following:\n");
+	while ((commit = get_revision(&rev)) != NULL) {
+		strbuf_addch(&out, '\n');
+		strbuf_addf(&out, "commit %s\n",
+			oid_to_hex(&commit->object.oid));
+		pretty_print_commit(&ctx, commit, &out);
+	}
+	write_file_buf(git_path_squash_msg(the_repository), out.buf, out.len);
+	strbuf_release(&out);
+}
+
+static void finish(struct commit *head_commit,
+		   struct commit_list *remoteheads,
+		   const struct object_id *new_head, const char *msg)
+{
+	struct strbuf reflog_message = STRBUF_INIT;
+	const struct object_id *head = &head_commit->object.oid;
+
+	if (!msg)
+		strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
+	else {
+		if (verbosity >= 0)
+			printf("%s\n", msg);
+		strbuf_addf(&reflog_message, "%s: %s",
+			getenv("GIT_REFLOG_ACTION"), msg);
+	}
+	if (squash) {
+		squash_message(head_commit, remoteheads);
+	} else {
+		if (verbosity >= 0 && !merge_msg.len)
+			printf(_("No merge message -- not updating HEAD\n"));
+		else {
+			const char *argv_gc_auto[] = { "gc", "--auto", NULL };
+			update_ref(reflog_message.buf, "HEAD", new_head, head,
+				   0, UPDATE_REFS_DIE_ON_ERR);
+			/*
+			 * We ignore errors in 'gc --auto', since the
+			 * user should see them.
+			 */
+			close_object_store(the_repository->objects);
+			run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
+		}
+	}
+	if (new_head && show_diffstat) {
+		struct diff_options opts;
+		repo_diff_setup(the_repository, &opts);
+		opts.stat_width = -1; /* use full terminal width */
+		opts.stat_graph_width = -1; /* respect statGraphWidth config */
+		opts.output_format |=
+			DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
+		opts.detect_rename = DIFF_DETECT_RENAME;
+		diff_setup_done(&opts);
+		diff_tree_oid(head, new_head, "", &opts);
+		diffcore_std(&opts);
+		diff_flush(&opts);
+	}
+
+	/* Run a post-merge hook */
+	run_hook_le(NULL, "post-merge", squash ? "1" : "0", NULL);
+
+	strbuf_release(&reflog_message);
+}
+
+/* Get the name for the merge commit's message. */
+static void merge_name(const char *remote, struct strbuf *msg)
+{
+	struct commit *remote_head;
+	struct object_id branch_head;
+	struct strbuf buf = STRBUF_INIT;
+	struct strbuf bname = STRBUF_INIT;
+	struct merge_remote_desc *desc;
+	const char *ptr;
+	char *found_ref;
+	int len, early;
+
+	strbuf_branchname(&bname, remote, 0);
+	remote = bname.buf;
+
+	oidclr(&branch_head);
+	remote_head = get_merge_parent(remote);
+	if (!remote_head)
+		die(_("'%s' does not point to a commit"), remote);
+
+	if (dwim_ref(remote, strlen(remote), &branch_head, &found_ref) > 0) {
+		if (starts_with(found_ref, "refs/heads/")) {
+			strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
+				    oid_to_hex(&branch_head), remote);
+			goto cleanup;
+		}
+		if (starts_with(found_ref, "refs/tags/")) {
+			strbuf_addf(msg, "%s\t\ttag '%s' of .\n",
+				    oid_to_hex(&branch_head), remote);
+			goto cleanup;
+		}
+		if (starts_with(found_ref, "refs/remotes/")) {
+			strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
+				    oid_to_hex(&branch_head), remote);
+			goto cleanup;
+		}
+	}
+
+	/* See if remote matches <name>^^^.. or <name>~<number> */
+	for (len = 0, ptr = remote + strlen(remote);
+	     remote < ptr && ptr[-1] == '^';
+	     ptr--)
+		len++;
+	if (len)
+		early = 1;
+	else {
+		early = 0;
+		ptr = strrchr(remote, '~');
+		if (ptr) {
+			int seen_nonzero = 0;
+
+			len++; /* count ~ */
+			while (*++ptr && isdigit(*ptr)) {
+				seen_nonzero |= (*ptr != '0');
+				len++;
+			}
+			if (*ptr)
+				len = 0; /* not ...~<number> */
+			else if (seen_nonzero)
+				early = 1;
+			else if (len == 1)
+				early = 1; /* "name~" is "name~1"! */
+		}
+	}
+	if (len) {
+		struct strbuf truname = STRBUF_INIT;
+		strbuf_addf(&truname, "refs/heads/%s", remote);
+		strbuf_setlen(&truname, truname.len - len);
+		if (ref_exists(truname.buf)) {
+			strbuf_addf(msg,
+				    "%s\t\tbranch '%s'%s of .\n",
+				    oid_to_hex(&remote_head->object.oid),
+				    truname.buf + 11,
+				    (early ? " (early part)" : ""));
+			strbuf_release(&truname);
+			goto cleanup;
+		}
+		strbuf_release(&truname);
+	}
+
+	desc = merge_remote_util(remote_head);
+	if (desc && desc->obj && desc->obj->type == OBJ_TAG) {
+		strbuf_addf(msg, "%s\t\t%s '%s'\n",
+			    oid_to_hex(&desc->obj->oid),
+			    type_name(desc->obj->type),
+			    remote);
+		goto cleanup;
+	}
+
+	strbuf_addf(msg, "%s\t\tcommit '%s'\n",
+		oid_to_hex(&remote_head->object.oid), remote);
+cleanup:
+	strbuf_release(&buf);
+	strbuf_release(&bname);
+}
+
+static void parse_branch_merge_options(char *bmo)
+{
+	const char **argv;
+	int argc;
+
+	if (!bmo)
+		return;
+	argc = split_cmdline(bmo, &argv);
+	if (argc < 0)
+		die(_("Bad branch.%s.mergeoptions string: %s"), branch,
+		    _(split_cmdline_strerror(argc)));
+	REALLOC_ARRAY(argv, argc + 2);
+	MOVE_ARRAY(argv + 1, argv, argc + 1);
+	argc++;
+	argv[0] = "branch.*.mergeoptions";
+	parse_options(argc, argv, NULL, builtin_merge_options,
+		      builtin_merge_usage, 0);
+	free(argv);
+}
+
+static int git_merge_config(const char *k, const char *v, void *cb)
+{
+	int status;
+
+	if (branch && starts_with(k, "branch.") &&
+		starts_with(k + 7, branch) &&
+		!strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
+		free(branch_mergeoptions);
+		branch_mergeoptions = xstrdup(v);
+		return 0;
+	}
+
+	if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
+		show_diffstat = git_config_bool(k, v);
+	else if (!strcmp(k, "merge.verifysignatures"))
+		verify_signatures = git_config_bool(k, v);
+	else if (!strcmp(k, "pull.twohead"))
+		return git_config_string(&pull_twohead, k, v);
+	else if (!strcmp(k, "pull.octopus"))
+		return git_config_string(&pull_octopus, k, v);
+	else if (!strcmp(k, "commit.cleanup"))
+		return git_config_string(&cleanup_arg, k, v);
+	else if (!strcmp(k, "merge.renormalize"))
+		option_renormalize = git_config_bool(k, v);
+	else if (!strcmp(k, "merge.ff")) {
+		int boolval = git_parse_maybe_bool(v);
+		if (0 <= boolval) {
+			fast_forward = boolval ? FF_ALLOW : FF_NO;
+		} else if (v && !strcmp(v, "only")) {
+			fast_forward = FF_ONLY;
+		} /* do not barf on values from future versions of git */
+		return 0;
+	} else if (!strcmp(k, "merge.defaulttoupstream")) {
+		default_to_upstream = git_config_bool(k, v);
+		return 0;
+	} else if (!strcmp(k, "commit.gpgsign")) {
+		sign_commit = git_config_bool(k, v) ? "" : NULL;
+		return 0;
+	}
+
+	status = fmt_merge_msg_config(k, v, cb);
+	if (status)
+		return status;
+	status = git_gpg_config(k, v, NULL);
+	if (status)
+		return status;
+	return git_diff_ui_config(k, v, cb);
+}
+
+static int read_tree_trivial(struct object_id *common, struct object_id *head,
+			     struct object_id *one)
+{
+	int i, nr_trees = 0;
+	struct tree *trees[MAX_UNPACK_TREES];
+	struct tree_desc t[MAX_UNPACK_TREES];
+	struct unpack_trees_options opts;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.head_idx = 2;
+	opts.src_index = &the_index;
+	opts.dst_index = &the_index;
+	opts.update = 1;
+	opts.verbose_update = 1;
+	opts.trivial_merges_only = 1;
+	opts.merge = 1;
+	trees[nr_trees] = parse_tree_indirect(common);
+	if (!trees[nr_trees++])
+		return -1;
+	trees[nr_trees] = parse_tree_indirect(head);
+	if (!trees[nr_trees++])
+		return -1;
+	trees[nr_trees] = parse_tree_indirect(one);
+	if (!trees[nr_trees++])
+		return -1;
+	opts.fn = threeway_merge;
+	cache_tree_free(&active_cache_tree);
+	for (i = 0; i < nr_trees; i++) {
+		parse_tree(trees[i]);
+		init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
+	}
+	if (unpack_trees(nr_trees, t, &opts))
+		return -1;
+	return 0;
+}
+
+static void write_tree_trivial(struct object_id *oid)
+{
+	if (write_cache_as_tree(oid, 0, NULL))
+		die(_("git write-tree failed to write a tree"));
+}
+
+static int try_merge_strategy(const char *strategy, struct commit_list *common,
+			      struct commit_list *remoteheads,
+			      struct commit *head)
+{
+	struct lock_file lock = LOCK_INIT;
+	const char *head_arg = "HEAD";
+
+	hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
+	refresh_cache(REFRESH_QUIET);
+	if (write_locked_index(&the_index, &lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		return error(_("Unable to write index."));
+
+	if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
+		int clean, x;
+		struct commit *result;
+		struct commit_list *reversed = NULL;
+		struct merge_options o;
+		struct commit_list *j;
+
+		if (remoteheads->next) {
+			error(_("Not handling anything other than two heads merge."));
+			return 2;
+		}
+
+		init_merge_options(&o, the_repository);
+		if (!strcmp(strategy, "subtree"))
+			o.subtree_shift = "";
+
+		o.renormalize = option_renormalize;
+		o.show_rename_progress =
+			show_progress == -1 ? isatty(2) : show_progress;
+
+		for (x = 0; x < xopts_nr; x++)
+			if (parse_merge_opt(&o, xopts[x]))
+				die(_("Unknown option for merge-recursive: -X%s"), xopts[x]);
+
+		o.branch1 = head_arg;
+		o.branch2 = merge_remote_util(remoteheads->item)->name;
+
+		for (j = common; j; j = j->next)
+			commit_list_insert(j->item, &reversed);
+
+		hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
+		clean = merge_recursive(&o, head,
+				remoteheads->item, reversed, &result);
+		if (clean < 0)
+			exit(128);
+		if (write_locked_index(&the_index, &lock,
+				       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+			die(_("unable to write %s"), get_index_file());
+		return clean ? 0 : 1;
+	} else {
+		return try_merge_command(the_repository,
+					 strategy, xopts_nr, xopts,
+					 common, head_arg, remoteheads);
+	}
+}
+
+static void count_diff_files(struct diff_queue_struct *q,
+			     struct diff_options *opt, void *data)
+{
+	int *count = data;
+
+	(*count) += q->nr;
+}
+
+static int count_unmerged_entries(void)
+{
+	int i, ret = 0;
+
+	for (i = 0; i < active_nr; i++)
+		if (ce_stage(active_cache[i]))
+			ret++;
+
+	return ret;
+}
+
+static void add_strategies(const char *string, unsigned attr)
+{
+	int i;
+
+	if (string) {
+		struct string_list list = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
+		string_list_split(&list, string, ' ', -1);
+		for_each_string_list_item(item, &list)
+			append_strategy(get_strategy(item->string));
+		string_list_clear(&list, 0);
+		return;
+	}
+	for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
+		if (all_strategy[i].attr & attr)
+			append_strategy(&all_strategy[i]);
+
+}
+
+static void read_merge_msg(struct strbuf *msg)
+{
+	const char *filename = git_path_merge_msg(the_repository);
+	strbuf_reset(msg);
+	if (strbuf_read_file(msg, filename, 0) < 0)
+		die_errno(_("Could not read from '%s'"), filename);
+}
+
+static void write_merge_state(struct commit_list *);
+static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
+{
+	if (err_msg)
+		error("%s", err_msg);
+	fprintf(stderr,
+		_("Not committing merge; use 'git commit' to complete the merge.\n"));
+	write_merge_state(remoteheads);
+	exit(1);
+}
+
+static const char merge_editor_comment[] =
+N_("Please enter a commit message to explain why this merge is necessary,\n"
+   "especially if it merges an updated upstream into a topic branch.\n"
+   "\n");
+
+static const char scissors_editor_comment[] =
+N_("An empty message aborts the commit.\n");
+
+static const char no_scissors_editor_comment[] =
+N_("Lines starting with '%c' will be ignored, and an empty message aborts\n"
+   "the commit.\n");
+
+static void write_merge_heads(struct commit_list *);
+static void prepare_to_commit(struct commit_list *remoteheads)
+{
+	struct strbuf msg = STRBUF_INIT;
+	strbuf_addbuf(&msg, &merge_msg);
+	if (squash)
+		BUG("the control must not reach here under --squash");
+	if (0 < option_edit) {
+		strbuf_addch(&msg, '\n');
+		if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS) {
+			wt_status_append_cut_line(&msg);
+			strbuf_commented_addf(&msg, "\n");
+		}
+		strbuf_commented_addf(&msg, _(merge_editor_comment));
+		strbuf_commented_addf(&msg, _(cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS ?
+			scissors_editor_comment :
+			no_scissors_editor_comment), comment_line_char);
+	}
+	if (signoff)
+		append_signoff(&msg, ignore_non_trailer(msg.buf, msg.len), 0);
+	write_merge_heads(remoteheads);
+	write_file_buf(git_path_merge_msg(the_repository), msg.buf, msg.len);
+	if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
+			    git_path_merge_msg(the_repository), "merge", NULL))
+		abort_commit(remoteheads, NULL);
+	if (0 < option_edit) {
+		if (launch_editor(git_path_merge_msg(the_repository), NULL, NULL))
+			abort_commit(remoteheads, NULL);
+	}
+
+	if (verify_msg && run_commit_hook(0 < option_edit, get_index_file(),
+					  "commit-msg",
+					  git_path_merge_msg(the_repository), NULL))
+		abort_commit(remoteheads, NULL);
+
+	read_merge_msg(&msg);
+	cleanup_message(&msg, cleanup_mode, 0);
+	if (!msg.len)
+		abort_commit(remoteheads, _("Empty commit message."));
+	strbuf_release(&merge_msg);
+	strbuf_addbuf(&merge_msg, &msg);
+	strbuf_release(&msg);
+}
+
+static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
+{
+	struct object_id result_tree, result_commit;
+	struct commit_list *parents, **pptr = &parents;
+	struct lock_file lock = LOCK_INIT;
+
+	hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
+	refresh_cache(REFRESH_QUIET);
+	if (write_locked_index(&the_index, &lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		return error(_("Unable to write index."));
+
+	write_tree_trivial(&result_tree);
+	printf(_("Wonderful.\n"));
+	pptr = commit_list_append(head, pptr);
+	pptr = commit_list_append(remoteheads->item, pptr);
+	prepare_to_commit(remoteheads);
+	if (commit_tree(merge_msg.buf, merge_msg.len, &result_tree, parents,
+			&result_commit, NULL, sign_commit))
+		die(_("failed to write commit object"));
+	finish(head, remoteheads, &result_commit, "In-index merge");
+	remove_merge_branch_state(the_repository);
+	return 0;
+}
+
+static int finish_automerge(struct commit *head,
+			    int head_subsumed,
+			    struct commit_list *common,
+			    struct commit_list *remoteheads,
+			    struct object_id *result_tree,
+			    const char *wt_strategy)
+{
+	struct commit_list *parents = NULL;
+	struct strbuf buf = STRBUF_INIT;
+	struct object_id result_commit;
+
+	write_tree_trivial(result_tree);
+	free_commit_list(common);
+	parents = remoteheads;
+	if (!head_subsumed || fast_forward == FF_NO)
+		commit_list_insert(head, &parents);
+	prepare_to_commit(remoteheads);
+	if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parents,
+			&result_commit, NULL, sign_commit))
+		die(_("failed to write commit object"));
+	strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
+	finish(head, remoteheads, &result_commit, buf.buf);
+	strbuf_release(&buf);
+	remove_merge_branch_state(the_repository);
+	return 0;
+}
+
+static int suggest_conflicts(void)
+{
+	const char *filename;
+	FILE *fp;
+	struct strbuf msgbuf = STRBUF_INIT;
+
+	filename = git_path_merge_msg(the_repository);
+	fp = xfopen(filename, "a");
+
+	/*
+	 * We can't use cleanup_mode because if we're not using the editor,
+	 * get_cleanup_mode will return COMMIT_MSG_CLEANUP_SPACE instead, even
+	 * though the message is meant to be processed later by git-commit.
+	 * Thus, we will get the cleanup mode which is returned when we _are_
+	 * using an editor.
+	 */
+	append_conflicts_hint(&the_index, &msgbuf,
+			      get_cleanup_mode(cleanup_arg, 1));
+	fputs(msgbuf.buf, fp);
+	strbuf_release(&msgbuf);
+	fclose(fp);
+	repo_rerere(the_repository, allow_rerere_auto);
+	printf(_("Automatic merge failed; "
+			"fix conflicts and then commit the result.\n"));
+	return 1;
+}
+
+static int evaluate_result(void)
+{
+	int cnt = 0;
+	struct rev_info rev;
+
+	/* Check how many files differ. */
+	repo_init_revisions(the_repository, &rev, "");
+	setup_revisions(0, NULL, &rev, NULL);
+	rev.diffopt.output_format |=
+		DIFF_FORMAT_CALLBACK;
+	rev.diffopt.format_callback = count_diff_files;
+	rev.diffopt.format_callback_data = &cnt;
+	run_diff_files(&rev, 0);
+
+	/*
+	 * Check how many unmerged entries are
+	 * there.
+	 */
+	cnt += count_unmerged_entries();
+
+	return cnt;
+}
+
+/*
+ * Pretend as if the user told us to merge with the remote-tracking
+ * branch we have for the upstream of the current branch
+ */
+static int setup_with_upstream(const char ***argv)
+{
+	struct branch *branch = branch_get(NULL);
+	int i;
+	const char **args;
+
+	if (!branch)
+		die(_("No current branch."));
+	if (!branch->remote_name)
+		die(_("No remote for the current branch."));
+	if (!branch->merge_nr)
+		die(_("No default upstream defined for the current branch."));
+
+	args = xcalloc(st_add(branch->merge_nr, 1), sizeof(char *));
+	for (i = 0; i < branch->merge_nr; i++) {
+		if (!branch->merge[i]->dst)
+			die(_("No remote-tracking branch for %s from %s"),
+			    branch->merge[i]->src, branch->remote_name);
+		args[i] = branch->merge[i]->dst;
+	}
+	args[i] = NULL;
+	*argv = args;
+	return i;
+}
+
+static void write_merge_heads(struct commit_list *remoteheads)
+{
+	struct commit_list *j;
+	struct strbuf buf = STRBUF_INIT;
+
+	for (j = remoteheads; j; j = j->next) {
+		struct object_id *oid;
+		struct commit *c = j->item;
+		struct merge_remote_desc *desc;
+
+		desc = merge_remote_util(c);
+		if (desc && desc->obj) {
+			oid = &desc->obj->oid;
+		} else {
+			oid = &c->object.oid;
+		}
+		strbuf_addf(&buf, "%s\n", oid_to_hex(oid));
+	}
+	write_file_buf(git_path_merge_head(the_repository), buf.buf, buf.len);
+
+	strbuf_reset(&buf);
+	if (fast_forward == FF_NO)
+		strbuf_addstr(&buf, "no-ff");
+	write_file_buf(git_path_merge_mode(the_repository), buf.buf, buf.len);
+	strbuf_release(&buf);
+}
+
+static void write_merge_state(struct commit_list *remoteheads)
+{
+	write_merge_heads(remoteheads);
+	strbuf_addch(&merge_msg, '\n');
+	write_file_buf(git_path_merge_msg(the_repository), merge_msg.buf,
+		       merge_msg.len);
+}
+
+static int default_edit_option(void)
+{
+	static const char name[] = "GIT_MERGE_AUTOEDIT";
+	const char *e = getenv(name);
+	struct stat st_stdin, st_stdout;
+
+	if (have_message)
+		/* an explicit -m msg without --[no-]edit */
+		return 0;
+
+	if (e) {
+		int v = git_parse_maybe_bool(e);
+		if (v < 0)
+			die(_("Bad value '%s' in environment '%s'"), e, name);
+		return v;
+	}
+
+	/* Use editor if stdin and stdout are the same and is a tty */
+	return (!fstat(0, &st_stdin) &&
+		!fstat(1, &st_stdout) &&
+		isatty(0) && isatty(1) &&
+		st_stdin.st_dev == st_stdout.st_dev &&
+		st_stdin.st_ino == st_stdout.st_ino &&
+		st_stdin.st_mode == st_stdout.st_mode);
+}
+
+static struct commit_list *reduce_parents(struct commit *head_commit,
+					  int *head_subsumed,
+					  struct commit_list *remoteheads)
+{
+	struct commit_list *parents, **remotes;
+
+	/*
+	 * Is the current HEAD reachable from another commit being
+	 * merged?  If so we do not want to record it as a parent of
+	 * the resulting merge, unless --no-ff is given.  We will flip
+	 * this variable to 0 when we find HEAD among the independent
+	 * tips being merged.
+	 */
+	*head_subsumed = 1;
+
+	/* Find what parents to record by checking independent ones. */
+	parents = reduce_heads(remoteheads);
+	free_commit_list(remoteheads);
+
+	remoteheads = NULL;
+	remotes = &remoteheads;
+	while (parents) {
+		struct commit *commit = pop_commit(&parents);
+		if (commit == head_commit)
+			*head_subsumed = 0;
+		else
+			remotes = &commit_list_insert(commit, remotes)->next;
+	}
+	return remoteheads;
+}
+
+static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *merge_msg)
+{
+	struct fmt_merge_msg_opts opts;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.add_title = !have_message;
+	opts.shortlog_len = shortlog_len;
+	opts.credit_people = (0 < option_edit);
+
+	fmt_merge_msg(merge_names, merge_msg, &opts);
+	if (merge_msg->len)
+		strbuf_setlen(merge_msg, merge_msg->len - 1);
+}
+
+static void handle_fetch_head(struct commit_list **remotes, struct strbuf *merge_names)
+{
+	const char *filename;
+	int fd, pos, npos;
+	struct strbuf fetch_head_file = STRBUF_INIT;
+	const unsigned hexsz = the_hash_algo->hexsz;
+
+	if (!merge_names)
+		merge_names = &fetch_head_file;
+
+	filename = git_path_fetch_head(the_repository);
+	fd = open(filename, O_RDONLY);
+	if (fd < 0)
+		die_errno(_("could not open '%s' for reading"), filename);
+
+	if (strbuf_read(merge_names, fd, 0) < 0)
+		die_errno(_("could not read '%s'"), filename);
+	if (close(fd) < 0)
+		die_errno(_("could not close '%s'"), filename);
+
+	for (pos = 0; pos < merge_names->len; pos = npos) {
+		struct object_id oid;
+		char *ptr;
+		struct commit *commit;
+
+		ptr = strchr(merge_names->buf + pos, '\n');
+		if (ptr)
+			npos = ptr - merge_names->buf + 1;
+		else
+			npos = merge_names->len;
+
+		if (npos - pos < hexsz + 2 ||
+		    get_oid_hex(merge_names->buf + pos, &oid))
+			commit = NULL; /* bad */
+		else if (memcmp(merge_names->buf + pos + hexsz, "\t\t", 2))
+			continue; /* not-for-merge */
+		else {
+			char saved = merge_names->buf[pos + hexsz];
+			merge_names->buf[pos + hexsz] = '\0';
+			commit = get_merge_parent(merge_names->buf + pos);
+			merge_names->buf[pos + hexsz] = saved;
+		}
+		if (!commit) {
+			if (ptr)
+				*ptr = '\0';
+			die(_("not something we can merge in %s: %s"),
+			    filename, merge_names->buf + pos);
+		}
+		remotes = &commit_list_insert(commit, remotes)->next;
+	}
+
+	if (merge_names == &fetch_head_file)
+		strbuf_release(&fetch_head_file);
+}
+
+static struct commit_list *collect_parents(struct commit *head_commit,
+					   int *head_subsumed,
+					   int argc, const char **argv,
+					   struct strbuf *merge_msg)
+{
+	int i;
+	struct commit_list *remoteheads = NULL;
+	struct commit_list **remotes = &remoteheads;
+	struct strbuf merge_names = STRBUF_INIT, *autogen = NULL;
+
+	if (merge_msg && (!have_message || shortlog_len))
+		autogen = &merge_names;
+
+	if (head_commit)
+		remotes = &commit_list_insert(head_commit, remotes)->next;
+
+	if (argc == 1 && !strcmp(argv[0], "FETCH_HEAD")) {
+		handle_fetch_head(remotes, autogen);
+		remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
+	} else {
+		for (i = 0; i < argc; i++) {
+			struct commit *commit = get_merge_parent(argv[i]);
+			if (!commit)
+				help_unknown_ref(argv[i], "merge",
+						 _("not something we can merge"));
+			remotes = &commit_list_insert(commit, remotes)->next;
+		}
+		remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
+		if (autogen) {
+			struct commit_list *p;
+			for (p = remoteheads; p; p = p->next)
+				merge_name(merge_remote_util(p->item)->name, autogen);
+		}
+	}
+
+	if (autogen) {
+		prepare_merge_message(autogen, merge_msg);
+		strbuf_release(autogen);
+	}
+
+	return remoteheads;
+}
+
+static int merging_a_throwaway_tag(struct commit *commit)
+{
+	char *tag_ref;
+	struct object_id oid;
+	int is_throwaway_tag = 0;
+
+	/* Are we merging a tag? */
+	if (!merge_remote_util(commit) ||
+	    !merge_remote_util(commit)->obj ||
+	    merge_remote_util(commit)->obj->type != OBJ_TAG)
+		return is_throwaway_tag;
+
+	/*
+	 * Now we know we are merging a tag object.  Are we downstream
+	 * and following the tags from upstream?  If so, we must have
+	 * the tag object pointed at by "refs/tags/$T" where $T is the
+	 * tagname recorded in the tag object.  We want to allow such
+	 * a "just to catch up" merge to fast-forward.
+	 *
+	 * Otherwise, we are playing an integrator's role, making a
+	 * merge with a throw-away tag from a contributor with
+	 * something like "git pull $contributor $signed_tag".
+	 * We want to forbid such a merge from fast-forwarding
+	 * by default; otherwise we would not keep the signature
+	 * anywhere.
+	 */
+	tag_ref = xstrfmt("refs/tags/%s",
+			  ((struct tag *)merge_remote_util(commit)->obj)->tag);
+	if (!read_ref(tag_ref, &oid) &&
+	    oideq(&oid, &merge_remote_util(commit)->obj->oid))
+		is_throwaway_tag = 0;
+	else
+		is_throwaway_tag = 1;
+	free(tag_ref);
+	return is_throwaway_tag;
+}
+
+int cmd_merge(int argc, const char **argv, const char *prefix)
+{
+	struct object_id result_tree, stash, head_oid;
+	struct commit *head_commit;
+	struct strbuf buf = STRBUF_INIT;
+	int i, ret = 0, head_subsumed;
+	int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
+	struct commit_list *common = NULL;
+	const char *best_strategy = NULL, *wt_strategy = NULL;
+	struct commit_list *remoteheads, *p;
+	void *branch_to_free;
+	int orig_argc = argc;
+
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage_with_options(builtin_merge_usage, builtin_merge_options);
+
+	/*
+	 * Check if we are _not_ on a detached HEAD, i.e. if there is a
+	 * current branch.
+	 */
+	branch = branch_to_free = resolve_refdup("HEAD", 0, &head_oid, NULL);
+	if (branch)
+		skip_prefix(branch, "refs/heads/", &branch);
+
+	init_diff_ui_defaults();
+	git_config(git_merge_config, NULL);
+
+	if (!branch || is_null_oid(&head_oid))
+		head_commit = NULL;
+	else
+		head_commit = lookup_commit_or_die(&head_oid, "HEAD");
+
+	if (branch_mergeoptions)
+		parse_branch_merge_options(branch_mergeoptions);
+	argc = parse_options(argc, argv, prefix, builtin_merge_options,
+			builtin_merge_usage, 0);
+	if (shortlog_len < 0)
+		shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;
+
+	if (verbosity < 0 && show_progress == -1)
+		show_progress = 0;
+
+	if (abort_current_merge) {
+		int nargc = 2;
+		const char *nargv[] = {"reset", "--merge", NULL};
+
+		if (orig_argc != 2)
+			usage_msg_opt(_("--abort expects no arguments"),
+			      builtin_merge_usage, builtin_merge_options);
+
+		if (!file_exists(git_path_merge_head(the_repository)))
+			die(_("There is no merge to abort (MERGE_HEAD missing)."));
+
+		/* Invoke 'git reset --merge' */
+		ret = cmd_reset(nargc, nargv, prefix);
+		goto done;
+	}
+
+	if (quit_current_merge) {
+		if (orig_argc != 2)
+			usage_msg_opt(_("--quit expects no arguments"),
+				      builtin_merge_usage,
+				      builtin_merge_options);
+
+		remove_merge_branch_state(the_repository);
+		goto done;
+	}
+
+	if (continue_current_merge) {
+		int nargc = 1;
+		const char *nargv[] = {"commit", NULL};
+
+		if (orig_argc != 2)
+			usage_msg_opt(_("--continue expects no arguments"),
+			      builtin_merge_usage, builtin_merge_options);
+
+		if (!file_exists(git_path_merge_head(the_repository)))
+			die(_("There is no merge in progress (MERGE_HEAD missing)."));
+
+		/* Invoke 'git commit' */
+		ret = cmd_commit(nargc, nargv, prefix);
+		goto done;
+	}
+
+	if (read_cache_unmerged())
+		die_resolve_conflict("merge");
+
+	if (file_exists(git_path_merge_head(the_repository))) {
+		/*
+		 * There is no unmerged entry, don't advise 'git
+		 * add/rm <file>', just 'git commit'.
+		 */
+		if (advice_resolve_conflict)
+			die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
+				  "Please, commit your changes before you merge."));
+		else
+			die(_("You have not concluded your merge (MERGE_HEAD exists)."));
+	}
+	if (file_exists(git_path_cherry_pick_head(the_repository))) {
+		if (advice_resolve_conflict)
+			die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
+			    "Please, commit your changes before you merge."));
+		else
+			die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
+	}
+	resolve_undo_clear();
+
+	if (option_edit < 0)
+		option_edit = default_edit_option();
+
+	cleanup_mode = get_cleanup_mode(cleanup_arg, 0 < option_edit);
+
+	if (verbosity < 0)
+		show_diffstat = 0;
+
+	if (squash) {
+		if (fast_forward == FF_NO)
+			die(_("You cannot combine --squash with --no-ff."));
+		if (option_commit > 0)
+			die(_("You cannot combine --squash with --commit."));
+		/*
+		 * squash can now silently disable option_commit - this is not
+		 * a problem as it is only overriding the default, not a user
+		 * supplied option.
+		 */
+		option_commit = 0;
+	}
+
+	if (option_commit < 0)
+		option_commit = 1;
+
+	if (!argc) {
+		if (default_to_upstream)
+			argc = setup_with_upstream(&argv);
+		else
+			die(_("No commit specified and merge.defaultToUpstream not set."));
+	} else if (argc == 1 && !strcmp(argv[0], "-")) {
+		argv[0] = "@{-1}";
+	}
+
+	if (!argc)
+		usage_with_options(builtin_merge_usage,
+			builtin_merge_options);
+
+	if (!head_commit) {
+		/*
+		 * If the merged head is a valid one there is no reason
+		 * to forbid "git merge" into a branch yet to be born.
+		 * We do the same for "git pull".
+		 */
+		struct object_id *remote_head_oid;
+		if (squash)
+			die(_("Squash commit into empty head not supported yet"));
+		if (fast_forward == FF_NO)
+			die(_("Non-fast-forward commit does not make sense into "
+			    "an empty head"));
+		remoteheads = collect_parents(head_commit, &head_subsumed,
+					      argc, argv, NULL);
+		if (!remoteheads)
+			die(_("%s - not something we can merge"), argv[0]);
+		if (remoteheads->next)
+			die(_("Can merge only exactly one commit into empty head"));
+
+		if (verify_signatures)
+			verify_merge_signature(remoteheads->item, verbosity);
+
+		remote_head_oid = &remoteheads->item->object.oid;
+		read_empty(remote_head_oid, 0);
+		update_ref("initial pull", "HEAD", remote_head_oid, NULL, 0,
+			   UPDATE_REFS_DIE_ON_ERR);
+		goto done;
+	}
+
+	/*
+	 * All the rest are the commits being merged; prepare
+	 * the standard merge summary message to be appended
+	 * to the given message.
+	 */
+	remoteheads = collect_parents(head_commit, &head_subsumed,
+				      argc, argv, &merge_msg);
+
+	if (!head_commit || !argc)
+		usage_with_options(builtin_merge_usage,
+			builtin_merge_options);
+
+	if (verify_signatures) {
+		for (p = remoteheads; p; p = p->next) {
+			verify_merge_signature(p->item, verbosity);
+		}
+	}
+
+	strbuf_addstr(&buf, "merge");
+	for (p = remoteheads; p; p = p->next)
+		strbuf_addf(&buf, " %s", merge_remote_util(p->item)->name);
+	setenv("GIT_REFLOG_ACTION", buf.buf, 0);
+	strbuf_reset(&buf);
+
+	for (p = remoteheads; p; p = p->next) {
+		struct commit *commit = p->item;
+		strbuf_addf(&buf, "GITHEAD_%s",
+			    oid_to_hex(&commit->object.oid));
+		setenv(buf.buf, merge_remote_util(commit)->name, 1);
+		strbuf_reset(&buf);
+		if (fast_forward != FF_ONLY && merging_a_throwaway_tag(commit))
+			fast_forward = FF_NO;
+	}
+
+	if (!use_strategies) {
+		if (!remoteheads)
+			; /* already up-to-date */
+		else if (!remoteheads->next)
+			add_strategies(pull_twohead, DEFAULT_TWOHEAD);
+		else
+			add_strategies(pull_octopus, DEFAULT_OCTOPUS);
+	}
+
+	for (i = 0; i < use_strategies_nr; i++) {
+		if (use_strategies[i]->attr & NO_FAST_FORWARD)
+			fast_forward = FF_NO;
+		if (use_strategies[i]->attr & NO_TRIVIAL)
+			allow_trivial = 0;
+	}
+
+	if (!remoteheads)
+		; /* already up-to-date */
+	else if (!remoteheads->next)
+		common = get_merge_bases(head_commit, remoteheads->item);
+	else {
+		struct commit_list *list = remoteheads;
+		commit_list_insert(head_commit, &list);
+		common = get_octopus_merge_bases(list);
+		free(list);
+	}
+
+	update_ref("updating ORIG_HEAD", "ORIG_HEAD",
+		   &head_commit->object.oid, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
+
+	if (remoteheads && !common) {
+		/* No common ancestors found. */
+		if (!allow_unrelated_histories)
+			die(_("refusing to merge unrelated histories"));
+		/* otherwise, we need a real merge. */
+	} else if (!remoteheads ||
+		 (!remoteheads->next && !common->next &&
+		  common->item == remoteheads->item)) {
+		/*
+		 * If head can reach all the merge then we are up to date.
+		 * but first the most common case of merging one remote.
+		 */
+		finish_up_to_date(_("Already up to date."));
+		goto done;
+	} else if (fast_forward != FF_NO && !remoteheads->next &&
+			!common->next &&
+			oideq(&common->item->object.oid, &head_commit->object.oid)) {
+		/* Again the most common case of merging one remote. */
+		struct strbuf msg = STRBUF_INIT;
+		struct commit *commit;
+
+		if (verbosity >= 0) {
+			printf(_("Updating %s..%s\n"),
+			       find_unique_abbrev(&head_commit->object.oid,
+						  DEFAULT_ABBREV),
+			       find_unique_abbrev(&remoteheads->item->object.oid,
+						  DEFAULT_ABBREV));
+		}
+		strbuf_addstr(&msg, "Fast-forward");
+		if (have_message)
+			strbuf_addstr(&msg,
+				" (no commit created; -m option ignored)");
+		commit = remoteheads->item;
+		if (!commit) {
+			ret = 1;
+			goto done;
+		}
+
+		if (checkout_fast_forward(the_repository,
+					  &head_commit->object.oid,
+					  &commit->object.oid,
+					  overwrite_ignore)) {
+			ret = 1;
+			goto done;
+		}
+
+		finish(head_commit, remoteheads, &commit->object.oid, msg.buf);
+		remove_merge_branch_state(the_repository);
+		goto done;
+	} else if (!remoteheads->next && common->next)
+		;
+		/*
+		 * We are not doing octopus and not fast-forward.  Need
+		 * a real merge.
+		 */
+	else if (!remoteheads->next && !common->next && option_commit) {
+		/*
+		 * We are not doing octopus, not fast-forward, and have
+		 * only one common.
+		 */
+		refresh_cache(REFRESH_QUIET);
+		if (allow_trivial && fast_forward != FF_ONLY) {
+			/* See if it is really trivial. */
+			git_committer_info(IDENT_STRICT);
+			printf(_("Trying really trivial in-index merge...\n"));
+			if (!read_tree_trivial(&common->item->object.oid,
+					       &head_commit->object.oid,
+					       &remoteheads->item->object.oid)) {
+				ret = merge_trivial(head_commit, remoteheads);
+				goto done;
+			}
+			printf(_("Nope.\n"));
+		}
+	} else {
+		/*
+		 * An octopus.  If we can reach all the remote we are up
+		 * to date.
+		 */
+		int up_to_date = 1;
+		struct commit_list *j;
+
+		for (j = remoteheads; j; j = j->next) {
+			struct commit_list *common_one;
+
+			/*
+			 * Here we *have* to calculate the individual
+			 * merge_bases again, otherwise "git merge HEAD^
+			 * HEAD^^" would be missed.
+			 */
+			common_one = get_merge_bases(head_commit, j->item);
+			if (!oideq(&common_one->item->object.oid, &j->item->object.oid)) {
+				up_to_date = 0;
+				break;
+			}
+		}
+		if (up_to_date) {
+			finish_up_to_date(_("Already up to date. Yeeah!"));
+			goto done;
+		}
+	}
+
+	if (fast_forward == FF_ONLY)
+		die(_("Not possible to fast-forward, aborting."));
+
+	/* We are going to make a new commit. */
+	git_committer_info(IDENT_STRICT);
+
+	/*
+	 * At this point, we need a real merge.  No matter what strategy
+	 * we use, it would operate on the index, possibly affecting the
+	 * working tree, and when resolved cleanly, have the desired
+	 * tree in the index -- this means that the index must be in
+	 * sync with the head commit.  The strategies are responsible
+	 * to ensure this.
+	 */
+	if (use_strategies_nr == 1 ||
+	    /*
+	     * Stash away the local changes so that we can try more than one.
+	     */
+	    save_state(&stash))
+		oidclr(&stash);
+
+	for (i = 0; !merge_was_ok && i < use_strategies_nr; i++) {
+		int ret, cnt;
+		if (i) {
+			printf(_("Rewinding the tree to pristine...\n"));
+			restore_state(&head_commit->object.oid, &stash);
+		}
+		if (use_strategies_nr != 1)
+			printf(_("Trying merge strategy %s...\n"),
+				use_strategies[i]->name);
+		/*
+		 * Remember which strategy left the state in the working
+		 * tree.
+		 */
+		wt_strategy = use_strategies[i]->name;
+
+		ret = try_merge_strategy(use_strategies[i]->name,
+					 common, remoteheads,
+					 head_commit);
+		/*
+		 * The backend exits with 1 when conflicts are
+		 * left to be resolved, with 2 when it does not
+		 * handle the given merge at all.
+		 */
+		if (ret < 2) {
+			if (!ret) {
+				if (option_commit) {
+					/* Automerge succeeded. */
+					automerge_was_ok = 1;
+					break;
+				}
+				merge_was_ok = 1;
+			}
+			cnt = evaluate_result();
+			if (best_cnt <= 0 || cnt <= best_cnt) {
+				best_strategy = use_strategies[i]->name;
+				best_cnt = cnt;
+			}
+		}
+	}
+
+	/*
+	 * If we have a resulting tree, that means the strategy module
+	 * auto resolved the merge cleanly.
+	 */
+	if (automerge_was_ok) {
+		ret = finish_automerge(head_commit, head_subsumed,
+				       common, remoteheads,
+				       &result_tree, wt_strategy);
+		goto done;
+	}
+
+	/*
+	 * Pick the result from the best strategy and have the user fix
+	 * it up.
+	 */
+	if (!best_strategy) {
+		restore_state(&head_commit->object.oid, &stash);
+		if (use_strategies_nr > 1)
+			fprintf(stderr,
+				_("No merge strategy handled the merge.\n"));
+		else
+			fprintf(stderr, _("Merge with strategy %s failed.\n"),
+				use_strategies[0]->name);
+		ret = 2;
+		goto done;
+	} else if (best_strategy == wt_strategy)
+		; /* We already have its result in the working tree. */
+	else {
+		printf(_("Rewinding the tree to pristine...\n"));
+		restore_state(&head_commit->object.oid, &stash);
+		printf(_("Using the %s to prepare resolving by hand.\n"),
+			best_strategy);
+		try_merge_strategy(best_strategy, common, remoteheads,
+				   head_commit);
+	}
+
+	if (squash)
+		finish(head_commit, remoteheads, NULL, NULL);
+	else
+		write_merge_state(remoteheads);
+
+	if (merge_was_ok)
+		fprintf(stderr, _("Automatic merge went well; "
+			"stopped before committing as requested\n"));
+	else
+		ret = suggest_conflicts();
+
+done:
+	free(branch_to_free);
+	return ret;
+}