builtin/replace.c - jrn/git - Git at Google

 /*
  * Builtin "git replace"
  *
  * Copyright (c) 2008 Christian Couder <chriscool@tuxfamily.org>
  *
  * Based on builtin/tag.c by Kristian Høgsberg <krh@redhat.com>
  * and Carlos Rica <jasampler@gmail.com> that was itself based on
  * git-tag.sh and mktag.c by Linus Torvalds.
  */

 #include "cache.h"
 #include "builtin.h"
 #include "refs.h"
 #include "parse-options.h"
 #include "run-command.h"
 #include "tag.h"

 static const char * const git_replace_usage[] = {
 	N_("git replace [-f] <object> <replacement>"),
 	N_("git replace [-f] --edit <object>"),
 	N_("git replace [-f] --graft <commit> [<parent>...]"),
 	N_("git replace -d <object>..."),
 	N_("git replace [--format=<format>] [-l [<pattern>]]"),
 	NULL
 };

 enum replace_format {
 	REPLACE_FORMAT_SHORT,
 	REPLACE_FORMAT_MEDIUM,
 	REPLACE_FORMAT_LONG
 };

 struct show_data {
 	const char *pattern;
 	enum replace_format format;
 };

 static int show_reference(const char *refname, const struct object_id *oid,
 			  int flag, void *cb_data)
 {
 	struct show_data *data = cb_data;

 	if (!wildmatch(data->pattern, refname, 0, NULL)) {
 		if (data->format == REPLACE_FORMAT_SHORT)
 			printf("%s\n", refname);
 		else if (data->format == REPLACE_FORMAT_MEDIUM)
 			printf("%s -> %s\n", refname, oid_to_hex(oid));
 		else { /* data->format == REPLACE_FORMAT_LONG */
 			struct object_id object;
 			enum object_type obj_type, repl_type;

 			if (get_sha1(refname, object.hash))
 				return error("Failed to resolve '%s' as a valid ref.", refname);

 			obj_type = sha1_object_info(object.hash, NULL);
 			repl_type = sha1_object_info(oid->hash, NULL);

 			printf("%s (%s) -> %s (%s)\n", refname, typename(obj_type),
 			       oid_to_hex(oid), typename(repl_type));
 		}
 	}

 	return 0;
 }

 static int list_replace_refs(const char *pattern, const char *format)
 {
 	struct show_data data;

 	if (pattern == NULL)
 		pattern = "*";
 	data.pattern = pattern;

 	if (format == NULL || *format == '\0' || !strcmp(format, "short"))
 		data.format = REPLACE_FORMAT_SHORT;
 	else if (!strcmp(format, "medium"))
 		data.format = REPLACE_FORMAT_MEDIUM;
 	else if (!strcmp(format, "long"))
 		data.format = REPLACE_FORMAT_LONG;
 	else
 		die("invalid replace format '%s'\n"
 		    "valid formats are 'short', 'medium' and 'long'\n",
 		    format);

 	for_each_replace_ref(show_reference, (void *)&data);

 	return 0;
 }

 typedef int (*each_replace_name_fn)(const char *name, const char *ref,
 				    const struct object_id *oid);

 static int for_each_replace_name(const char **argv, each_replace_name_fn fn)
 {
 	const char **p, *full_hex;
 	struct strbuf ref = STRBUF_INIT;
 	size_t base_len;
 	int had_error = 0;
 	struct object_id oid;

 	strbuf_addstr(&ref, git_replace_ref_base);
 	base_len = ref.len;

 	for (p = argv; *p; p++) {
 		if (get_oid(*p, &oid)) {
 			error("Failed to resolve '%s' as a valid ref.", *p);
 			had_error = 1;
 			continue;
 		}

 		strbuf_setlen(&ref, base_len);
 		strbuf_addstr(&ref, oid_to_hex(&oid));
 		full_hex = ref.buf + base_len;

 		if (read_ref(ref.buf, oid.hash)) {
 			error("replace ref '%s' not found.", full_hex);
 			had_error = 1;
 			continue;
 		}
 		if (fn(full_hex, ref.buf, &oid))
 			had_error = 1;
 	}
 	strbuf_release(&ref);
 	return had_error;
 }

 static int delete_replace_ref(const char *name, const char *ref,
 			      const struct object_id *oid)
 {
 	if (delete_ref(NULL, ref, oid->hash, 0))
 		return 1;
 	printf("Deleted replace ref '%s'\n", name);
 	return 0;
 }

 static void check_ref_valid(struct object_id *object,
 			    struct object_id *prev,
 			    struct strbuf *ref,
 			    int force)
 {
 	strbuf_reset(ref);
 	strbuf_addf(ref, "%s%s", git_replace_ref_base, oid_to_hex(object));
 	if (check_refname_format(ref->buf, 0))
 		die("'%s' is not a valid ref name.", ref->buf);

 	if (read_ref(ref->buf, prev->hash))
 		oidclr(prev);
 	else if (!force)
 		die("replace ref '%s' already exists", ref->buf);
 }

 static int replace_object_oid(const char *object_ref,
 			       struct object_id *object,
 			       const char *replace_ref,
 			       struct object_id *repl,
 			       int force)
 {
 	struct object_id prev;
 	enum object_type obj_type, repl_type;
 	struct strbuf ref = STRBUF_INIT;
 	struct ref_transaction *transaction;
 	struct strbuf err = STRBUF_INIT;

 	obj_type = sha1_object_info(object->hash, NULL);
 	repl_type = sha1_object_info(repl->hash, NULL);
 	if (!force && obj_type != repl_type)
 		die("Objects must be of the same type.\n"
 		    "'%s' points to a replaced object of type '%s'\n"
 		    "while '%s' points to a replacement object of type '%s'.",
 		    object_ref, typename(obj_type),
 		    replace_ref, typename(repl_type));

 	check_ref_valid(object, &prev, &ref, force);

 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref.buf, repl->hash, prev.hash,
 				   0, NULL, &err) ||
 	    ref_transaction_commit(transaction, &err))
 		die("%s", err.buf);

 	ref_transaction_free(transaction);
 	strbuf_release(&ref);
 	return 0;
 }

 static int replace_object(const char *object_ref, const char *replace_ref, int force)
 {
 	struct object_id object, repl;

 	if (get_oid(object_ref, &object))
 		die("Failed to resolve '%s' as a valid ref.", object_ref);
 	if (get_oid(replace_ref, &repl))
 		die("Failed to resolve '%s' as a valid ref.", replace_ref);

 	return replace_object_oid(object_ref, &object, replace_ref, &repl, force);
 }

 /*
  * Write the contents of the object named by "sha1" to the file "filename".
  * If "raw" is true, then the object's raw contents are printed according to
  * "type". Otherwise, we pretty-print the contents for human editing.
  */
 static void export_object(const struct object_id *oid, enum object_type type,
 			  int raw, const char *filename)
 {
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	int fd;

 	fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
 	if (fd < 0)
 		die_errno("unable to open %s for writing", filename);

 	argv_array_push(&cmd.args, "--no-replace-objects");
 	argv_array_push(&cmd.args, "cat-file");
 	if (raw)
 		argv_array_push(&cmd.args, typename(type));
 	else
 		argv_array_push(&cmd.args, "-p");
 	argv_array_push(&cmd.args, oid_to_hex(oid));
 	cmd.git_cmd = 1;
 	cmd.out = fd;

 	if (run_command(&cmd))
 		die("cat-file reported failure");
 }

 /*
  * Read a previously-exported (and possibly edited) object back from "filename",
  * interpreting it as "type", and writing the result to the object database.
  * The sha1 of the written object is returned via sha1.
  */
 static void import_object(struct object_id *oid, enum object_type type,
 			  int raw, const char *filename)
 {
 	int fd;

 	fd = open(filename, O_RDONLY);
 	if (fd < 0)
 		die_errno("unable to open %s for reading", filename);

 	if (!raw && type == OBJ_TREE) {
 		const char *argv[] = { "mktree", NULL };
 		struct child_process cmd = CHILD_PROCESS_INIT;
 		struct strbuf result = STRBUF_INIT;

 		cmd.argv = argv;
 		cmd.git_cmd = 1;
 		cmd.in = fd;
 		cmd.out = -1;

 		if (start_command(&cmd))
 			die("unable to spawn mktree");

 		if (strbuf_read(&result, cmd.out, 41) < 0)
 			die_errno("unable to read from mktree");
 		close(cmd.out);

 		if (finish_command(&cmd))
 			die("mktree reported failure");
 		if (get_oid_hex(result.buf, oid) < 0)
 			die("mktree did not return an object name");

 		strbuf_release(&result);
 	} else {
 		struct stat st;
 		int flags = HASH_FORMAT_CHECK | HASH_WRITE_OBJECT;

 		if (fstat(fd, &st) < 0)
 			die_errno("unable to fstat %s", filename);
 		if (index_fd(oid->hash, fd, &st, type, NULL, flags) < 0)
 			die("unable to write object to database");
 		/* index_fd close()s fd for us */
 	}

 	/*
 	 * No need to close(fd) here; both run-command and index-fd
 	 * will have done it for us.
 	 */
 }

 static int edit_and_replace(const char *object_ref, int force, int raw)
 {
 	char *tmpfile = git_pathdup("REPLACE_EDITOBJ");
 	enum object_type type;
 	struct object_id old, new, prev;
 	struct strbuf ref = STRBUF_INIT;

 	if (get_oid(object_ref, &old) < 0)
 		die("Not a valid object name: '%s'", object_ref);

 	type = sha1_object_info(old.hash, NULL);
 	if (type < 0)
 		die("unable to get object type for %s", oid_to_hex(&old));

 	check_ref_valid(&old, &prev, &ref, force);
 	strbuf_release(&ref);

 	export_object(&old, type, raw, tmpfile);
 	if (launch_editor(tmpfile, NULL, NULL) < 0)
 		die("editing object file failed");
 	import_object(&new, type, raw, tmpfile);

 	free(tmpfile);

 	if (!oidcmp(&old, &new))
 		return error("new object is the same as the old one: '%s'", oid_to_hex(&old));

 	return replace_object_oid(object_ref, &old, "replacement", &new, force);
 }

 static void replace_parents(struct strbuf *buf, int argc, const char **argv)
 {
 	struct strbuf new_parents = STRBUF_INIT;
 	const char *parent_start, *parent_end;
 	int i;

 	/* find existing parents */
 	parent_start = buf->buf;
 	parent_start += GIT_SHA1_HEXSZ + 6; /* "tree " + "hex sha1" + "\n" */
 	parent_end = parent_start;

 	while (starts_with(parent_end, "parent "))
 		parent_end += 48; /* "parent " + "hex sha1" + "\n" */

 	/* prepare new parents */
 	for (i = 0; i < argc; i++) {
 		struct object_id oid;
 		if (get_oid(argv[i], &oid) < 0)
 			die(_("Not a valid object name: '%s'"), argv[i]);
 		lookup_commit_or_die(oid.hash, argv[i]);
 		strbuf_addf(&new_parents, "parent %s\n", oid_to_hex(&oid));
 	}

 	/* replace existing parents with new ones */
 	strbuf_splice(buf, parent_start - buf->buf, parent_end - parent_start,
 		      new_parents.buf, new_parents.len);

 	strbuf_release(&new_parents);
 }

 struct check_mergetag_data {
 	int argc;
 	const char **argv;
 };

 static void check_one_mergetag(struct commit *commit,
 			       struct commit_extra_header *extra,
 			       void *data)
 {
 	struct check_mergetag_data *mergetag_data = (struct check_mergetag_data *)data;
 	const char *ref = mergetag_data->argv[0];
 	struct object_id tag_oid;
 	struct tag *tag;
 	int i;

 	hash_sha1_file(extra->value, extra->len, typename(OBJ_TAG), tag_oid.hash);
 	tag = lookup_tag(tag_oid.hash);
 	if (!tag)
 		die(_("bad mergetag in commit '%s'"), ref);
 	if (parse_tag_buffer(tag, extra->value, extra->len))
 		die(_("malformed mergetag in commit '%s'"), ref);

 	/* iterate over new parents */
 	for (i = 1; i < mergetag_data->argc; i++) {
 		struct object_id oid;
 		if (get_sha1(mergetag_data->argv[i], oid.hash) < 0)
 			die(_("Not a valid object name: '%s'"), mergetag_data->argv[i]);
 		if (!oidcmp(&tag->tagged->oid, &oid))
 			return; /* found */
 	}

 	die(_("original commit '%s' contains mergetag '%s' that is discarded; "
 	      "use --edit instead of --graft"), ref, oid_to_hex(&tag_oid));
 }

 static void check_mergetags(struct commit *commit, int argc, const char **argv)
 {
 	struct check_mergetag_data mergetag_data;

 	mergetag_data.argc = argc;
 	mergetag_data.argv = argv;
 	for_each_mergetag(check_one_mergetag, commit, &mergetag_data);
 }

 static int create_graft(int argc, const char **argv, int force)
 {
 	struct object_id old, new;
 	const char *old_ref = argv[0];
 	struct commit *commit;
 	struct strbuf buf = STRBUF_INIT;
 	const char *buffer;
 	unsigned long size;

 	if (get_oid(old_ref, &old) < 0)
 		die(_("Not a valid object name: '%s'"), old_ref);
 	commit = lookup_commit_or_die(old.hash, old_ref);

 	buffer = get_commit_buffer(commit, &size);
 	strbuf_add(&buf, buffer, size);
 	unuse_commit_buffer(commit, buffer);

 	replace_parents(&buf, argc - 1, &argv[1]);

 	if (remove_signature(&buf)) {
 		warning(_("the original commit '%s' has a gpg signature."), old_ref);
 		warning(_("the signature will be removed in the replacement commit!"));
 	}

 	check_mergetags(commit, argc, argv);

 	if (write_sha1_file(buf.buf, buf.len, commit_type, new.hash))
 		die(_("could not write replacement commit for: '%s'"), old_ref);

 	strbuf_release(&buf);

 	if (!oidcmp(&old, &new))
 		return error("new commit is the same as the old one: '%s'", oid_to_hex(&old));

 	return replace_object_oid(old_ref, &old, "replacement", &new, force);
 }

 int cmd_replace(int argc, const char **argv, const char *prefix)
 {
 	int force = 0;
 	int raw = 0;
 	const char *format = NULL;
 	enum {
 		MODE_UNSPECIFIED = 0,
 		MODE_LIST,
 		MODE_DELETE,
 		MODE_EDIT,
 		MODE_GRAFT,
 		MODE_REPLACE
 	} cmdmode = MODE_UNSPECIFIED;
 	struct option options[] = {
 		OPT_CMDMODE('l', "list", &cmdmode, N_("list replace refs"), MODE_LIST),
 		OPT_CMDMODE('d', "delete", &cmdmode, N_("delete replace refs"), MODE_DELETE),
 		OPT_CMDMODE('e', "edit", &cmdmode, N_("edit existing object"), MODE_EDIT),
 		OPT_CMDMODE('g', "graft", &cmdmode, N_("change a commit's parents"), MODE_GRAFT),
 		OPT_BOOL('f', "force", &force, N_("replace the ref if it exists")),
 		OPT_BOOL(0, "raw", &raw, N_("do not pretty-print contents for --edit")),
 		OPT_STRING(0, "format", &format, N_("format"), N_("use this format")),
 		OPT_END()
 	};

 	check_replace_refs = 0;
 	git_config(git_default_config, NULL);

 	argc = parse_options(argc, argv, prefix, options, git_replace_usage, 0);

 	if (!cmdmode)
 		cmdmode = argc ? MODE_REPLACE : MODE_LIST;

 	if (format && cmdmode != MODE_LIST)
 		usage_msg_opt("--format cannot be used when not listing",
 			      git_replace_usage, options);

 	if (force &&
 	    cmdmode != MODE_REPLACE &&
 	    cmdmode != MODE_EDIT &&
 	    cmdmode != MODE_GRAFT)
 		usage_msg_opt("-f only makes sense when writing a replacement",
 			      git_replace_usage, options);

 	if (raw && cmdmode != MODE_EDIT)
 		usage_msg_opt("--raw only makes sense with --edit",
 			      git_replace_usage, options);

 	switch (cmdmode) {
 	case MODE_DELETE:
 		if (argc < 1)
 			usage_msg_opt("-d needs at least one argument",
 				      git_replace_usage, options);
 		return for_each_replace_name(argv, delete_replace_ref);

 	case MODE_REPLACE:
 		if (argc != 2)
 			usage_msg_opt("bad number of arguments",
 				      git_replace_usage, options);
 		return replace_object(argv[0], argv[1], force);

 	case MODE_EDIT:
 		if (argc != 1)
 			usage_msg_opt("-e needs exactly one argument",
 				      git_replace_usage, options);
 		return edit_and_replace(argv[0], force, raw);

 	case MODE_GRAFT:
 		if (argc < 1)
 			usage_msg_opt("-g needs at least one argument",
 				      git_replace_usage, options);
 		return create_graft(argc, argv, force);

 	case MODE_LIST:
 		if (argc > 1)
 			usage_msg_opt("only one pattern can be given with -l",
 				      git_replace_usage, options);
 		return list_replace_refs(argv[0], format);

 	default:
 		die("BUG: invalid cmdmode %d", (int)cmdmode);
 	}
 }
	/*
	* Builtin "git replace"
	*
	* Copyright (c) 2008 Christian Couder <chriscool@tuxfamily.org>
	*
	* Based on builtin/tag.c by Kristian Høgsberg <krh@redhat.com>
	* and Carlos Rica <jasampler@gmail.com> that was itself based on
	* git-tag.sh and mktag.c by Linus Torvalds.
	*/

	#include "cache.h"
	#include "builtin.h"
	#include "refs.h"
	#include "parse-options.h"
	#include "run-command.h"
	#include "tag.h"

	static const char * const git_replace_usage[] = {
	N_("git replace [-f] <object> <replacement>"),
	N_("git replace [-f] --edit <object>"),
	N_("git replace [-f] --graft <commit> [<parent>...]"),
	N_("git replace -d <object>..."),
	N_("git replace [--format=<format>] [-l [<pattern>]]"),
	NULL
	};

	enum replace_format {
	REPLACE_FORMAT_SHORT,
	REPLACE_FORMAT_MEDIUM,
	REPLACE_FORMAT_LONG
	};

	struct show_data {
	const char *pattern;
	enum replace_format format;
	};

	static int show_reference(const char refname, const struct object_id oid,
	int flag, void *cb_data)
	{
	struct show_data *data = cb_data;

	if (!wildmatch(data->pattern, refname, 0, NULL)) {
	if (data->format == REPLACE_FORMAT_SHORT)
	printf("%s\n", refname);
	else if (data->format == REPLACE_FORMAT_MEDIUM)
	printf("%s -> %s\n", refname, oid_to_hex(oid));
	else { /* data->format == REPLACE_FORMAT_LONG */
	struct object_id object;
	enum object_type obj_type, repl_type;

	if (get_sha1(refname, object.hash))
	return error("Failed to resolve '%s' as a valid ref.", refname);

	obj_type = sha1_object_info(object.hash, NULL);
	repl_type = sha1_object_info(oid->hash, NULL);

	printf("%s (%s) -> %s (%s)\n", refname, typename(obj_type),
	oid_to_hex(oid), typename(repl_type));
	}
	}

	return 0;
	}

	static int list_replace_refs(const char pattern, const char format)
	{
	struct show_data data;

	if (pattern == NULL)
	pattern = "*";
	data.pattern = pattern;

	if (format == NULL \|\| *format == '\0' \|\| !strcmp(format, "short"))
	data.format = REPLACE_FORMAT_SHORT;
	else if (!strcmp(format, "medium"))
	data.format = REPLACE_FORMAT_MEDIUM;
	else if (!strcmp(format, "long"))
	data.format = REPLACE_FORMAT_LONG;
	else
	die("invalid replace format '%s'\n"
	"valid formats are 'short', 'medium' and 'long'\n",
	format);

	for_each_replace_ref(show_reference, (void *)&data);

	return 0;
	}

	typedef int (each_replace_name_fn)(const char name, const char *ref,
	const struct object_id *oid);

	static int for_each_replace_name(const char **argv, each_replace_name_fn fn)
	{
	const char *p, full_hex;
	struct strbuf ref = STRBUF_INIT;
	size_t base_len;
	int had_error = 0;
	struct object_id oid;

	strbuf_addstr(&ref, git_replace_ref_base);
	base_len = ref.len;

	for (p = argv; *p; p++) {
	if (get_oid(*p, &oid)) {
	error("Failed to resolve '%s' as a valid ref.", *p);
	had_error = 1;
	continue;
	}

	strbuf_setlen(&ref, base_len);
	strbuf_addstr(&ref, oid_to_hex(&oid));
	full_hex = ref.buf + base_len;

	if (read_ref(ref.buf, oid.hash)) {
	error("replace ref '%s' not found.", full_hex);
	had_error = 1;
	continue;
	}
	if (fn(full_hex, ref.buf, &oid))
	had_error = 1;
	}
	strbuf_release(&ref);
	return had_error;
	}

	static int delete_replace_ref(const char name, const char ref,
	const struct object_id *oid)
	{
	if (delete_ref(NULL, ref, oid->hash, 0))
	return 1;
	printf("Deleted replace ref '%s'\n", name);
	return 0;
	}

	static void check_ref_valid(struct object_id *object,
	struct object_id *prev,
	struct strbuf *ref,
	int force)
	{
	strbuf_reset(ref);
	strbuf_addf(ref, "%s%s", git_replace_ref_base, oid_to_hex(object));
	if (check_refname_format(ref->buf, 0))
	die("'%s' is not a valid ref name.", ref->buf);

	if (read_ref(ref->buf, prev->hash))
	oidclr(prev);
	else if (!force)
	die("replace ref '%s' already exists", ref->buf);
	}

	static int replace_object_oid(const char *object_ref,
	struct object_id *object,
	const char *replace_ref,
	struct object_id *repl,
	int force)
	{
	struct object_id prev;
	enum object_type obj_type, repl_type;
	struct strbuf ref = STRBUF_INIT;
	struct ref_transaction *transaction;
	struct strbuf err = STRBUF_INIT;

	obj_type = sha1_object_info(object->hash, NULL);
	repl_type = sha1_object_info(repl->hash, NULL);
	if (!force && obj_type != repl_type)
	die("Objects must be of the same type.\n"
	"'%s' points to a replaced object of type '%s'\n"
	"while '%s' points to a replacement object of type '%s'.",
	object_ref, typename(obj_type),
	replace_ref, typename(repl_type));

	check_ref_valid(object, &prev, &ref, force);

	transaction = ref_transaction_begin(&err);
	if (!transaction \|\|
	ref_transaction_update(transaction, ref.buf, repl->hash, prev.hash,
	0, NULL, &err) \|\|
	ref_transaction_commit(transaction, &err))
	die("%s", err.buf);

	ref_transaction_free(transaction);
	strbuf_release(&ref);
	return 0;
	}

	static int replace_object(const char object_ref, const char replace_ref, int force)
	{
	struct object_id object, repl;

	if (get_oid(object_ref, &object))
	die("Failed to resolve '%s' as a valid ref.", object_ref);
	if (get_oid(replace_ref, &repl))
	die("Failed to resolve '%s' as a valid ref.", replace_ref);

	return replace_object_oid(object_ref, &object, replace_ref, &repl, force);
	}

	/*
	* Write the contents of the object named by "sha1" to the file "filename".
	* If "raw" is true, then the object's raw contents are printed according to
	* "type". Otherwise, we pretty-print the contents for human editing.
	*/
	static void export_object(const struct object_id *oid, enum object_type type,
	int raw, const char *filename)
	{
	struct child_process cmd = CHILD_PROCESS_INIT;
	int fd;

	fd = open(filename, O_WRONLY \| O_CREAT \| O_TRUNC, 0666);
	if (fd < 0)
	die_errno("unable to open %s for writing", filename);

	argv_array_push(&cmd.args, "--no-replace-objects");
	argv_array_push(&cmd.args, "cat-file");
	if (raw)
	argv_array_push(&cmd.args, typename(type));
	else
	argv_array_push(&cmd.args, "-p");
	argv_array_push(&cmd.args, oid_to_hex(oid));
	cmd.git_cmd = 1;
	cmd.out = fd;

	if (run_command(&cmd))
	die("cat-file reported failure");
	}

	/*
	* Read a previously-exported (and possibly edited) object back from "filename",
	* interpreting it as "type", and writing the result to the object database.
	* The sha1 of the written object is returned via sha1.
	*/
	static void import_object(struct object_id *oid, enum object_type type,
	int raw, const char *filename)
	{
	int fd;

	fd = open(filename, O_RDONLY);
	if (fd < 0)
	die_errno("unable to open %s for reading", filename);

	if (!raw && type == OBJ_TREE) {
	const char *argv[] = { "mktree", NULL };
	struct child_process cmd = CHILD_PROCESS_INIT;
	struct strbuf result = STRBUF_INIT;

	cmd.argv = argv;
	cmd.git_cmd = 1;
	cmd.in = fd;
	cmd.out = -1;

	if (start_command(&cmd))
	die("unable to spawn mktree");

	if (strbuf_read(&result, cmd.out, 41) < 0)
	die_errno("unable to read from mktree");
	close(cmd.out);

	if (finish_command(&cmd))
	die("mktree reported failure");
	if (get_oid_hex(result.buf, oid) < 0)
	die("mktree did not return an object name");

	strbuf_release(&result);
	} else {
	struct stat st;
	int flags = HASH_FORMAT_CHECK \| HASH_WRITE_OBJECT;

	if (fstat(fd, &st) < 0)
	die_errno("unable to fstat %s", filename);
	if (index_fd(oid->hash, fd, &st, type, NULL, flags) < 0)
	die("unable to write object to database");
	/* index_fd close()s fd for us */
	}

	/*
	* No need to close(fd) here; both run-command and index-fd
	* will have done it for us.
	*/
	}

	static int edit_and_replace(const char *object_ref, int force, int raw)
	{
	char *tmpfile = git_pathdup("REPLACE_EDITOBJ");
	enum object_type type;
	struct object_id old, new, prev;
	struct strbuf ref = STRBUF_INIT;

	if (get_oid(object_ref, &old) < 0)
	die("Not a valid object name: '%s'", object_ref);

	type = sha1_object_info(old.hash, NULL);
	if (type < 0)
	die("unable to get object type for %s", oid_to_hex(&old));

	check_ref_valid(&old, &prev, &ref, force);
	strbuf_release(&ref);

	export_object(&old, type, raw, tmpfile);
	if (launch_editor(tmpfile, NULL, NULL) < 0)
	die("editing object file failed");
	import_object(&new, type, raw, tmpfile);

	free(tmpfile);

	if (!oidcmp(&old, &new))
	return error("new object is the same as the old one: '%s'", oid_to_hex(&old));

	return replace_object_oid(object_ref, &old, "replacement", &new, force);
	}

	static void replace_parents(struct strbuf buf, int argc, const char *argv)
	{
	struct strbuf new_parents = STRBUF_INIT;
	const char parent_start, parent_end;
	int i;

	/* find existing parents */
	parent_start = buf->buf;
	parent_start += GIT_SHA1_HEXSZ + 6; /* "tree " + "hex sha1" + "\n" */
	parent_end = parent_start;

	while (starts_with(parent_end, "parent "))
	parent_end += 48; /* "parent " + "hex sha1" + "\n" */

	/* prepare new parents */
	for (i = 0; i < argc; i++) {
	struct object_id oid;
	if (get_oid(argv[i], &oid) < 0)
	die(_("Not a valid object name: '%s'"), argv[i]);
	lookup_commit_or_die(oid.hash, argv[i]);
	strbuf_addf(&new_parents, "parent %s\n", oid_to_hex(&oid));
	}

	/* replace existing parents with new ones */
	strbuf_splice(buf, parent_start - buf->buf, parent_end - parent_start,
	new_parents.buf, new_parents.len);

	strbuf_release(&new_parents);
	}

	struct check_mergetag_data {
	int argc;
	const char **argv;
	};

	static void check_one_mergetag(struct commit *commit,
	struct commit_extra_header *extra,
	void *data)
	{
	struct check_mergetag_data mergetag_data = (struct check_mergetag_data )data;
	const char *ref = mergetag_data->argv[0];
	struct object_id tag_oid;
	struct tag *tag;
	int i;

	hash_sha1_file(extra->value, extra->len, typename(OBJ_TAG), tag_oid.hash);
	tag = lookup_tag(tag_oid.hash);
	if (!tag)
	die(_("bad mergetag in commit '%s'"), ref);
	if (parse_tag_buffer(tag, extra->value, extra->len))
	die(_("malformed mergetag in commit '%s'"), ref);

	/* iterate over new parents */
	for (i = 1; i < mergetag_data->argc; i++) {
	struct object_id oid;
	if (get_sha1(mergetag_data->argv[i], oid.hash) < 0)
	die(_("Not a valid object name: '%s'"), mergetag_data->argv[i]);
	if (!oidcmp(&tag->tagged->oid, &oid))
	return; /* found */
	}

	die(_("original commit '%s' contains mergetag '%s' that is discarded; "
	"use --edit instead of --graft"), ref, oid_to_hex(&tag_oid));
	}

	static void check_mergetags(struct commit commit, int argc, const char *argv)
	{
	struct check_mergetag_data mergetag_data;

	mergetag_data.argc = argc;
	mergetag_data.argv = argv;
	for_each_mergetag(check_one_mergetag, commit, &mergetag_data);
	}

	static int create_graft(int argc, const char **argv, int force)
	{
	struct object_id old, new;
	const char *old_ref = argv[0];
	struct commit *commit;
	struct strbuf buf = STRBUF_INIT;
	const char *buffer;
	unsigned long size;

	if (get_oid(old_ref, &old) < 0)
	die(_("Not a valid object name: '%s'"), old_ref);
	commit = lookup_commit_or_die(old.hash, old_ref);

	buffer = get_commit_buffer(commit, &size);
	strbuf_add(&buf, buffer, size);
	unuse_commit_buffer(commit, buffer);

	replace_parents(&buf, argc - 1, &argv[1]);

	if (remove_signature(&buf)) {
	warning(_("the original commit '%s' has a gpg signature."), old_ref);
	warning(_("the signature will be removed in the replacement commit!"));
	}

	check_mergetags(commit, argc, argv);

	if (write_sha1_file(buf.buf, buf.len, commit_type, new.hash))
	die(_("could not write replacement commit for: '%s'"), old_ref);

	strbuf_release(&buf);

	if (!oidcmp(&old, &new))
	return error("new commit is the same as the old one: '%s'", oid_to_hex(&old));

	return replace_object_oid(old_ref, &old, "replacement", &new, force);
	}

	int cmd_replace(int argc, const char *argv, const char prefix)
	{
	int force = 0;
	int raw = 0;
	const char *format = NULL;
	enum {
	MODE_UNSPECIFIED = 0,
	MODE_LIST,
	MODE_DELETE,
	MODE_EDIT,
	MODE_GRAFT,
	MODE_REPLACE
	} cmdmode = MODE_UNSPECIFIED;
	struct option options[] = {
	OPT_CMDMODE('l', "list", &cmdmode, N_("list replace refs"), MODE_LIST),
	OPT_CMDMODE('d', "delete", &cmdmode, N_("delete replace refs"), MODE_DELETE),
	OPT_CMDMODE('e', "edit", &cmdmode, N_("edit existing object"), MODE_EDIT),
	OPT_CMDMODE('g', "graft", &cmdmode, N_("change a commit's parents"), MODE_GRAFT),
	OPT_BOOL('f', "force", &force, N_("replace the ref if it exists")),
	OPT_BOOL(0, "raw", &raw, N_("do not pretty-print contents for --edit")),
	OPT_STRING(0, "format", &format, N_("format"), N_("use this format")),
	OPT_END()
	};

	check_replace_refs = 0;
	git_config(git_default_config, NULL);

	argc = parse_options(argc, argv, prefix, options, git_replace_usage, 0);

	if (!cmdmode)
	cmdmode = argc ? MODE_REPLACE : MODE_LIST;

	if (format && cmdmode != MODE_LIST)
	usage_msg_opt("--format cannot be used when not listing",
	git_replace_usage, options);

	if (force &&
	cmdmode != MODE_REPLACE &&
	cmdmode != MODE_EDIT &&
	cmdmode != MODE_GRAFT)
	usage_msg_opt("-f only makes sense when writing a replacement",
	git_replace_usage, options);

	if (raw && cmdmode != MODE_EDIT)
	usage_msg_opt("--raw only makes sense with --edit",
	git_replace_usage, options);

	switch (cmdmode) {
	case MODE_DELETE:
	if (argc < 1)
	usage_msg_opt("-d needs at least one argument",
	git_replace_usage, options);
	return for_each_replace_name(argv, delete_replace_ref);

	case MODE_REPLACE:
	if (argc != 2)
	usage_msg_opt("bad number of arguments",
	git_replace_usage, options);
	return replace_object(argv[0], argv[1], force);

	case MODE_EDIT:
	if (argc != 1)
	usage_msg_opt("-e needs exactly one argument",
	git_replace_usage, options);
	return edit_and_replace(argv[0], force, raw);

	case MODE_GRAFT:
	if (argc < 1)
	usage_msg_opt("-g needs at least one argument",
	git_replace_usage, options);
	return create_graft(argc, argv, force);

	case MODE_LIST:
	if (argc > 1)
	usage_msg_opt("only one pattern can be given with -l",
	git_replace_usage, options);
	return list_replace_refs(argv[0], format);

	default:
	die("BUG: invalid cmdmode %d", (int)cmdmode);
	}
	}