Merge branch 'pt/pull-builtin'

Reimplement 'git pull' in C.

* pt/pull-builtin:
  pull: remove redirection to git-pull.sh
  pull --rebase: error on no merge candidate cases
  pull --rebase: exit early when the working directory is dirty
  pull: configure --rebase via branch.<name>.rebase or pull.rebase
  pull: teach git pull about --rebase
  pull: set reflog message
  pull: implement pulling into an unborn branch
  pull: fast-forward working tree if head is updated
  pull: check if in unresolved merge state
  pull: support pull.ff config
  pull: error on no merge candidates
  pull: pass git-fetch's options to git-fetch
  pull: pass git-merge's options to git-merge
  pull: pass verbosity, --progress flags to fetch and merge
  pull: implement fetch + merge
  pull: implement skeletal builtin pull
  argv-array: implement argv_array_pushv()
  parse-options-cb: implement parse_opt_passthru_argv()
  parse-options-cb: implement parse_opt_passthru()

13 files changed, 992 insertions, 1 deletions

diff --git a/Documentation/technical/api-argv-array.txt b/Documentation/technical/api-argv-array.txt
index 1a797812fb..8076172a08 100644
--- a/Documentation/technical/api-argv-array.txt
+++ b/Documentation/technical/api-argv-array.txt
@@ -46,6 +46,9 @@ Functions
 	Format a string and push it onto the end of the array. This is a
 	convenience wrapper combining `strbuf_addf` and `argv_array_push`.
 
+`argv_array_pushv`::
+	Push a null-terminated array of strings onto the end of the array.
+
 `argv_array_pop`::
 	Remove the final element from the array. If there are no
 	elements in the array, do nothing.
diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt
index 525cb2f87a..5f0757dcc9 100644
--- a/Documentation/technical/api-parse-options.txt
+++ b/Documentation/technical/api-parse-options.txt
@@ -218,6 +218,19 @@ There are some macros to easily define options:
 	Use it to hide deprecated options that are still to be recognized
 	and ignored silently.
 
+`OPT_PASSTHRU(short, long, &char_var, arg_str, description, flags)`::
+	Introduce an option that will be reconstructed into a char* string,
+	which must be initialized to NULL. This is useful when you need to
+	pass the command-line option to another command. Any previous value
+	will be overwritten, so this should only be used for options where
+	the last one specified on the command line wins.
+
+`OPT_PASSTHRU_ARGV(short, long, &argv_array_var, arg_str, description, flags)`::
+	Introduce an option where all instances of it on the command-line will
+	be reconstructed into an argv_array. This is useful when you need to
+	pass the command-line option, which can be specified multiple times,
+	to another command.
+
 
 The last element of the array must be `OPT_END()`.
 
diff --git a/Makefile b/Makefile
index 9d00528612..7efedbe834 100644
--- a/Makefile
+++ b/Makefile
@@ -475,7 +475,6 @@ SCRIPT_SH += git-merge-octopus.sh
 SCRIPT_SH += git-merge-one-file.sh
 SCRIPT_SH += git-merge-resolve.sh
 SCRIPT_SH += git-mergetool.sh
-SCRIPT_SH += git-pull.sh
 SCRIPT_SH += git-quiltimport.sh
 SCRIPT_SH += git-rebase.sh
 SCRIPT_SH += git-remote-testgit.sh
@@ -879,6 +878,7 @@ BUILTIN_OBJS += builtin/pack-refs.o
 BUILTIN_OBJS += builtin/patch-id.o
 BUILTIN_OBJS += builtin/prune-packed.o
 BUILTIN_OBJS += builtin/prune.o
+BUILTIN_OBJS += builtin/pull.o
 BUILTIN_OBJS += builtin/push.o
 BUILTIN_OBJS += builtin/read-tree.o
 BUILTIN_OBJS += builtin/receive-pack.o
diff --git a/advice.c b/advice.c
index 575bec20b3..4965686e19 100644
--- a/advice.c
+++ b/advice.c
@@ -96,6 +96,14 @@ void NORETURN die_resolve_conflict(const char *me)
 	die("Exiting because of an unresolved conflict.");
 }
 
+void NORETURN die_conclude_merge(void)
+{
+	error(_("You have not concluded your merge (MERGE_HEAD exists)."));
+	if (advice_resolve_conflict)
+		advise(_("Please, commit your changes before you can merge."));
+	die(_("Exiting because of unfinished merge."));
+}
+
 void detach_advice(const char *new_name)
 {
 	const char fmt[] =
diff --git a/advice.h b/advice.h
index 5ecc6c154e..b341a55ce7 100644
--- a/advice.h
+++ b/advice.h
@@ -24,6 +24,7 @@ __attribute__((format (printf, 1, 2)))
 void advise(const char *advice, ...);
 int error_resolve_conflict(const char *me);
 extern void NORETURN die_resolve_conflict(const char *me);
+void NORETURN die_conclude_merge(void);
 void detach_advice(const char *new_name);
 
 #endif /* ADVICE_H */
diff --git a/argv-array.c b/argv-array.c
index 256741d226..eaed47712b 100644
--- a/argv-array.c
+++ b/argv-array.c
@@ -49,6 +49,12 @@ void argv_array_pushl(struct argv_array *array, ...)
 	va_end(ap);
 }
 
+void argv_array_pushv(struct argv_array *array, const char **argv)
+{
+	for (; *argv; argv++)
+		argv_array_push(array, *argv);
+}
+
 void argv_array_pop(struct argv_array *array)
 {
 	if (!array->argc)
diff --git a/argv-array.h b/argv-array.h
index c65e6e825a..a2fa0aa606 100644
--- a/argv-array.h
+++ b/argv-array.h
@@ -17,6 +17,7 @@ __attribute__((format (printf,2,3)))
 void argv_array_pushf(struct argv_array *, const char *fmt, ...);
 LAST_ARG_MUST_BE_NULL
 void argv_array_pushl(struct argv_array *, ...);
+void argv_array_pushv(struct argv_array *, const char **);
 void argv_array_pop(struct argv_array *);
 void argv_array_clear(struct argv_array *);
 
diff --git a/builtin.h b/builtin.h
index 9e04f979bc..839483de6e 100644
--- a/builtin.h
+++ b/builtin.h
@@ -98,6 +98,7 @@ extern int cmd_pack_redundant(int argc, const char **argv, const char *prefix);
 extern int cmd_patch_id(int argc, const char **argv, const char *prefix);
 extern int cmd_prune(int argc, const char **argv, const char *prefix);
 extern int cmd_prune_packed(int argc, const char **argv, const char *prefix);
+extern int cmd_pull(int argc, const char **argv, const char *prefix);
 extern int cmd_push(int argc, const char **argv, const char *prefix);
 extern int cmd_read_tree(int argc, const char **argv, const char *prefix);
 extern int cmd_receive_pack(int argc, const char **argv, const char *prefix);
diff --git a/builtin/pull.c b/builtin/pull.c
new file mode 100644
index 0000000000..722a83c51b
--- /dev/null
+++ b/builtin/pull.c
@@ -0,0 +1,882 @@
+/*
+ * Builtin "git pull"
+ *
+ * Based on git-pull.sh by Junio C Hamano
+ *
+ * Fetch one or more remote refs and merge it/them into the current HEAD.
+ */
+#include "cache.h"
+#include "builtin.h"
+#include "parse-options.h"
+#include "exec_cmd.h"
+#include "run-command.h"
+#include "sha1-array.h"
+#include "remote.h"
+#include "dir.h"
+#include "refs.h"
+#include "revision.h"
+#include "lockfile.h"
+
+enum rebase_type {
+	REBASE_INVALID = -1,
+	REBASE_FALSE = 0,
+	REBASE_TRUE,
+	REBASE_PRESERVE
+};
+
+/**
+ * Parses the value of --rebase. If value is a false value, returns
+ * REBASE_FALSE. If value is a true value, returns REBASE_TRUE. If value is
+ * "preserve", returns REBASE_PRESERVE. If value is a invalid value, dies with
+ * a fatal error if fatal is true, otherwise returns REBASE_INVALID.
+ */
+static enum rebase_type parse_config_rebase(const char *key, const char *value,
+		int fatal)
+{
+	int v = git_config_maybe_bool("pull.rebase", value);
+
+	if (!v)
+		return REBASE_FALSE;
+	else if (v > 0)
+		return REBASE_TRUE;
+	else if (!strcmp(value, "preserve"))
+		return REBASE_PRESERVE;
+
+	if (fatal)
+		die(_("Invalid value for %s: %s"), key, value);
+	else
+		error(_("Invalid value for %s: %s"), key, value);
+
+	return REBASE_INVALID;
+}
+
+/**
+ * Callback for --rebase, which parses arg with parse_config_rebase().
+ */
+static int parse_opt_rebase(const struct option *opt, const char *arg, int unset)
+{
+	enum rebase_type *value = opt->value;
+
+	if (arg)
+		*value = parse_config_rebase("--rebase", arg, 0);
+	else
+		*value = unset ? REBASE_FALSE : REBASE_TRUE;
+	return *value == REBASE_INVALID ? -1 : 0;
+}
+
+static const char * const pull_usage[] = {
+	N_("git pull [options] [<repository> [<refspec>...]]"),
+	NULL
+};
+
+/* Shared options */
+static int opt_verbosity;
+static char *opt_progress;
+
+/* Options passed to git-merge or git-rebase */
+static enum rebase_type opt_rebase = -1;
+static char *opt_diffstat;
+static char *opt_log;
+static char *opt_squash;
+static char *opt_commit;
+static char *opt_edit;
+static char *opt_ff;
+static char *opt_verify_signatures;
+static struct argv_array opt_strategies = ARGV_ARRAY_INIT;
+static struct argv_array opt_strategy_opts = ARGV_ARRAY_INIT;
+static char *opt_gpg_sign;
+
+/* Options passed to git-fetch */
+static char *opt_all;
+static char *opt_append;
+static char *opt_upload_pack;
+static int opt_force;
+static char *opt_tags;
+static char *opt_prune;
+static char *opt_recurse_submodules;
+static int opt_dry_run;
+static char *opt_keep;
+static char *opt_depth;
+static char *opt_unshallow;
+static char *opt_update_shallow;
+static char *opt_refmap;
+
+static struct option pull_options[] = {
+	/* Shared options */
+	OPT__VERBOSITY(&opt_verbosity),
+	OPT_PASSTHRU(0, "progress", &opt_progress, NULL,
+		N_("force progress reporting"),
+		PARSE_OPT_NOARG),
+
+	/* Options passed to git-merge or git-rebase */
+	OPT_GROUP(N_("Options related to merging")),
+	{ OPTION_CALLBACK, 'r', "rebase", &opt_rebase,
+	  N_("false|true|preserve"),
+	  N_("incorporate changes by rebasing rather than merging"),
+	  PARSE_OPT_OPTARG, parse_opt_rebase },
+	OPT_PASSTHRU('n', NULL, &opt_diffstat, NULL,
+		N_("do not show a diffstat at the end of the merge"),
+		PARSE_OPT_NOARG | PARSE_OPT_NONEG),
+	OPT_PASSTHRU(0, "stat", &opt_diffstat, NULL,
+		N_("show a diffstat at the end of the merge"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "summary", &opt_diffstat, NULL,
+		N_("(synonym to --stat)"),
+		PARSE_OPT_NOARG | PARSE_OPT_HIDDEN),
+	OPT_PASSTHRU(0, "log", &opt_log, N_("n"),
+		N_("add (at most <n>) entries from shortlog to merge commit message"),
+		PARSE_OPT_OPTARG),
+	OPT_PASSTHRU(0, "squash", &opt_squash, NULL,
+		N_("create a single commit instead of doing a merge"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "commit", &opt_commit, NULL,
+		N_("perform a commit if the merge succeeds (default)"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "edit", &opt_edit, NULL,
+		N_("edit message before committing"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "ff", &opt_ff, NULL,
+		N_("allow fast-forward"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "ff-only", &opt_ff, NULL,
+		N_("abort if fast-forward is not possible"),
+		PARSE_OPT_NOARG | PARSE_OPT_NONEG),
+	OPT_PASSTHRU(0, "verify-signatures", &opt_verify_signatures, NULL,
+		N_("verify that the named commit has a valid GPG signature"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU_ARGV('s', "strategy", &opt_strategies, N_("strategy"),
+		N_("merge strategy to use"),
+		0),
+	OPT_PASSTHRU_ARGV('X', "strategy-option", &opt_strategy_opts,
+		N_("option=value"),
+		N_("option for selected merge strategy"),
+		0),
+	OPT_PASSTHRU('S', "gpg-sign", &opt_gpg_sign, N_("key-id"),
+		N_("GPG sign commit"),
+		PARSE_OPT_OPTARG),
+
+	/* Options passed to git-fetch */
+	OPT_GROUP(N_("Options related to fetching")),
+	OPT_PASSTHRU(0, "all", &opt_all, NULL,
+		N_("fetch from all remotes"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU('a', "append", &opt_append, NULL,
+		N_("append to .git/FETCH_HEAD instead of overwriting"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "upload-pack", &opt_upload_pack, N_("path"),
+		N_("path to upload pack on remote end"),
+		0),
+	OPT__FORCE(&opt_force, N_("force overwrite of local branch")),
+	OPT_PASSTHRU('t', "tags", &opt_tags, NULL,
+		N_("fetch all tags and associated objects"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU('p', "prune", &opt_prune, NULL,
+		N_("prune remote-tracking branches no longer on remote"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "recurse-submodules", &opt_recurse_submodules,
+		N_("on-demand"),
+		N_("control recursive fetching of submodules"),
+		PARSE_OPT_OPTARG),
+	OPT_BOOL(0, "dry-run", &opt_dry_run,
+		N_("dry run")),
+	OPT_PASSTHRU('k', "keep", &opt_keep, NULL,
+		N_("keep downloaded pack"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "depth", &opt_depth, N_("depth"),
+		N_("deepen history of shallow clone"),
+		0),
+	OPT_PASSTHRU(0, "unshallow", &opt_unshallow, NULL,
+		N_("convert to a complete repository"),
+		PARSE_OPT_NONEG | PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "update-shallow", &opt_update_shallow, NULL,
+		N_("accept refs that update .git/shallow"),
+		PARSE_OPT_NOARG),
+	OPT_PASSTHRU(0, "refmap", &opt_refmap, N_("refmap"),
+		N_("specify fetch refmap"),
+		PARSE_OPT_NONEG),
+
+	OPT_END()
+};
+
+/**
+ * Pushes "-q" or "-v" switches into arr to match the opt_verbosity level.
+ */
+static void argv_push_verbosity(struct argv_array *arr)
+{
+	int verbosity;
+
+	for (verbosity = opt_verbosity; verbosity > 0; verbosity--)
+		argv_array_push(arr, "-v");
+
+	for (verbosity = opt_verbosity; verbosity < 0; verbosity++)
+		argv_array_push(arr, "-q");
+}
+
+/**
+ * Pushes "-f" switches into arr to match the opt_force level.
+ */
+static void argv_push_force(struct argv_array *arr)
+{
+	int force = opt_force;
+	while (force-- > 0)
+		argv_array_push(arr, "-f");
+}
+
+/**
+ * Sets the GIT_REFLOG_ACTION environment variable to the concatenation of argv
+ */
+static void set_reflog_message(int argc, const char **argv)
+{
+	int i;
+	struct strbuf msg = STRBUF_INIT;
+
+	for (i = 0; i < argc; i++) {
+		if (i)
+			strbuf_addch(&msg, ' ');
+		strbuf_addstr(&msg, argv[i]);
+	}
+
+	setenv("GIT_REFLOG_ACTION", msg.buf, 0);
+
+	strbuf_release(&msg);
+}
+
+/**
+ * If pull.ff is unset, returns NULL. If pull.ff is "true", returns "--ff". If
+ * pull.ff is "false", returns "--no-ff". If pull.ff is "only", returns
+ * "--ff-only". Otherwise, if pull.ff is set to an invalid value, die with an
+ * error.
+ */
+static const char *config_get_ff(void)
+{
+	const char *value;
+
+	if (git_config_get_value("pull.ff", &value))
+		return NULL;
+
+	switch (git_config_maybe_bool("pull.ff", value)) {
+	case 0:
+		return "--no-ff";
+	case 1:
+		return "--ff";
+	}
+
+	if (!strcmp(value, "only"))
+		return "--ff-only";
+
+	die(_("Invalid value for pull.ff: %s"), value);
+}
+
+/**
+ * Returns the default configured value for --rebase. It first looks for the
+ * value of "branch.$curr_branch.rebase", where $curr_branch is the current
+ * branch, and if HEAD is detached or the configuration key does not exist,
+ * looks for the value of "pull.rebase". If both configuration keys do not
+ * exist, returns REBASE_FALSE.
+ */
+static enum rebase_type config_get_rebase(void)
+{
+	struct branch *curr_branch = branch_get("HEAD");
+	const char *value;
+
+	if (curr_branch) {
+		char *key = xstrfmt("branch.%s.rebase", curr_branch->name);
+
+		if (!git_config_get_value(key, &value)) {
+			enum rebase_type ret = parse_config_rebase(key, value, 1);
+			free(key);
+			return ret;
+		}
+
+		free(key);
+	}
+
+	if (!git_config_get_value("pull.rebase", &value))
+		return parse_config_rebase("pull.rebase", value, 1);
+
+	return REBASE_FALSE;
+}
+
+/**
+ * Returns 1 if there are unstaged changes, 0 otherwise.
+ */
+static int has_unstaged_changes(const char *prefix)
+{
+	struct rev_info rev_info;
+	int result;
+
+	init_revisions(&rev_info, prefix);
+	DIFF_OPT_SET(&rev_info.diffopt, IGNORE_SUBMODULES);
+	DIFF_OPT_SET(&rev_info.diffopt, QUICK);
+	diff_setup_done(&rev_info.diffopt);
+	result = run_diff_files(&rev_info, 0);
+	return diff_result_code(&rev_info.diffopt, result);
+}
+
+/**
+ * Returns 1 if there are uncommitted changes, 0 otherwise.
+ */
+static int has_uncommitted_changes(const char *prefix)
+{
+	struct rev_info rev_info;
+	int result;
+
+	if (is_cache_unborn())
+		return 0;
+
+	init_revisions(&rev_info, prefix);
+	DIFF_OPT_SET(&rev_info.diffopt, IGNORE_SUBMODULES);
+	DIFF_OPT_SET(&rev_info.diffopt, QUICK);
+	add_head_to_pending(&rev_info);
+	diff_setup_done(&rev_info.diffopt);
+	result = run_diff_index(&rev_info, 1);
+	return diff_result_code(&rev_info.diffopt, result);
+}
+
+/**
+ * If the work tree has unstaged or uncommitted changes, dies with the
+ * appropriate message.
+ */
+static void die_on_unclean_work_tree(const char *prefix)
+{
+	struct lock_file *lock_file = xcalloc(1, sizeof(*lock_file));
+	int do_die = 0;
+
+	hold_locked_index(lock_file, 0);
+	refresh_cache(REFRESH_QUIET);
+	update_index_if_able(&the_index, lock_file);
+	rollback_lock_file(lock_file);
+
+	if (has_unstaged_changes(prefix)) {
+		error(_("Cannot pull with rebase: You have unstaged changes."));
+		do_die = 1;
+	}
+
+	if (has_uncommitted_changes(prefix)) {
+		if (do_die)
+			error(_("Additionally, your index contains uncommitted changes."));
+		else
+			error(_("Cannot pull with rebase: Your index contains uncommitted changes."));
+		do_die = 1;
+	}
+
+	if (do_die)
+		exit(1);
+}
+
+/**
+ * Appends merge candidates from FETCH_HEAD that are not marked not-for-merge
+ * into merge_heads.
+ */
+static void get_merge_heads(struct sha1_array *merge_heads)
+{
+	const char *filename = git_path("FETCH_HEAD");
+	FILE *fp;
+	struct strbuf sb = STRBUF_INIT;
+	unsigned char sha1[GIT_SHA1_RAWSZ];
+
+	if (!(fp = fopen(filename, "r")))
+		die_errno(_("could not open '%s' for reading"), filename);
+	while (strbuf_getline(&sb, fp, '\n') != EOF) {
+		if (get_sha1_hex(sb.buf, sha1))
+			continue;  /* invalid line: does not start with SHA1 */
+		if (starts_with(sb.buf + GIT_SHA1_HEXSZ, "\tnot-for-merge\t"))
+			continue;  /* ref is not-for-merge */
+		sha1_array_append(merge_heads, sha1);
+	}
+	fclose(fp);
+	strbuf_release(&sb);
+}
+
+/**
+ * Used by die_no_merge_candidates() as a for_each_remote() callback to
+ * retrieve the name of the remote if the repository only has one remote.
+ */
+static int get_only_remote(struct remote *remote, void *cb_data)
+{
+	const char **remote_name = cb_data;
+
+	if (*remote_name)
+		return -1;
+
+	*remote_name = remote->name;
+	return 0;
+}
+
+/**
+ * Dies with the appropriate reason for why there are no merge candidates:
+ *
+ * 1. We fetched from a specific remote, and a refspec was given, but it ended
+ *    up not fetching anything. This is usually because the user provided a
+ *    wildcard refspec which had no matches on the remote end.
+ *
+ * 2. We fetched from a non-default remote, but didn't specify a branch to
+ *    merge. We can't use the configured one because it applies to the default
+ *    remote, thus the user must specify the branches to merge.
+ *
+ * 3. We fetched from the branch's or repo's default remote, but:
+ *
+ *    a. We are not on a branch, so there will never be a configured branch to
+ *       merge with.
+ *
+ *    b. We are on a branch, but there is no configured branch to merge with.
+ *
+ * 4. We fetched from the branch's or repo's default remote, but the configured
+ *    branch to merge didn't get fetched. (Either it doesn't exist, or wasn't
+ *    part of the configured fetch refspec.)
+ */
+static void NORETURN die_no_merge_candidates(const char *repo, const char **refspecs)
+{
+	struct branch *curr_branch = branch_get("HEAD");
+	const char *remote = curr_branch ? curr_branch->remote_name : NULL;
+
+	if (*refspecs) {
+		if (opt_rebase)
+			fprintf_ln(stderr, _("There is no candidate for rebasing against among the refs that you just fetched."));
+		else
+			fprintf_ln(stderr, _("There are no candidates for merging among the refs that you just fetched."));
+		fprintf_ln(stderr, _("Generally this means that you provided a wildcard refspec which had no\n"
+					"matches on the remote end."));
+	} else if (repo && curr_branch && (!remote || strcmp(repo, remote))) {
+		fprintf_ln(stderr, _("You asked to pull from the remote '%s', but did not specify\n"
+			"a branch. Because this is not the default configured remote\n"
+			"for your current branch, you must specify a branch on the command line."),
+			repo);
+	} else if (!curr_branch) {
+		fprintf_ln(stderr, _("You are not currently on a branch."));
+		if (opt_rebase)
+			fprintf_ln(stderr, _("Please specify which branch you want to rebase against."));
+		else
+			fprintf_ln(stderr, _("Please specify which branch you want to merge with."));
+		fprintf_ln(stderr, _("See git-pull(1) for details."));
+		fprintf(stderr, "\n");
+		fprintf_ln(stderr, "    git pull <remote> <branch>");
+		fprintf(stderr, "\n");
+	} else if (!curr_branch->merge_nr) {
+		const char *remote_name = NULL;
+
+		if (for_each_remote(get_only_remote, &remote_name) || !remote_name)
+			remote_name = "<remote>";
+
+		fprintf_ln(stderr, _("There is no tracking information for the current branch."));
+		if (opt_rebase)
+			fprintf_ln(stderr, _("Please specify which branch you want to rebase against."));
+		else
+			fprintf_ln(stderr, _("Please specify which branch you want to merge with."));
+		fprintf_ln(stderr, _("See git-pull(1) for details."));
+		fprintf(stderr, "\n");
+		fprintf_ln(stderr, "    git pull <remote> <branch>");
+		fprintf(stderr, "\n");
+		fprintf_ln(stderr, _("If you wish to set tracking information for this branch you can do so with:\n"
+				"\n"
+				"    git branch --set-upstream-to=%s/<branch> %s\n"),
+				remote_name, curr_branch->name);
+	} else
+		fprintf_ln(stderr, _("Your configuration specifies to merge with the ref '%s'\n"
+			"from the remote, but no such ref was fetched."),
+			*curr_branch->merge_name);
+	exit(1);
+}
+
+/**
+ * Parses argv into [<repo> [<refspecs>...]], returning their values in `repo`
+ * as a string and `refspecs` as a null-terminated array of strings. If `repo`
+ * is not provided in argv, it is set to NULL.
+ */
+static void parse_repo_refspecs(int argc, const char **argv, const char **repo,
+		const char ***refspecs)
+{
+	if (argc > 0) {
+		*repo = *argv++;
+		argc--;
+	} else
+		*repo = NULL;
+	*refspecs = argv;
+}
+
+/**
+ * Runs git-fetch, returning its exit status. `repo` and `refspecs` are the
+ * repository and refspecs to fetch, or NULL if they are not provided.
+ */
+static int run_fetch(const char *repo, const char **refspecs)
+{
+	struct argv_array args = ARGV_ARRAY_INIT;
+	int ret;
+
+	argv_array_pushl(&args, "fetch", "--update-head-ok", NULL);
+
+	/* Shared options */
+	argv_push_verbosity(&args);
+	if (opt_progress)
+		argv_array_push(&args, opt_progress);
+
+	/* Options passed to git-fetch */
+	if (opt_all)
+		argv_array_push(&args, opt_all);
+	if (opt_append)
+		argv_array_push(&args, opt_append);
+	if (opt_upload_pack)
+		argv_array_push(&args, opt_upload_pack);
+	argv_push_force(&args);
+	if (opt_tags)
+		argv_array_push(&args, opt_tags);
+	if (opt_prune)
+		argv_array_push(&args, opt_prune);
+	if (opt_recurse_submodules)
+		argv_array_push(&args, opt_recurse_submodules);
+	if (opt_dry_run)
+		argv_array_push(&args, "--dry-run");
+	if (opt_keep)
+		argv_array_push(&args, opt_keep);
+	if (opt_depth)
+		argv_array_push(&args, opt_depth);
+	if (opt_unshallow)
+		argv_array_push(&args, opt_unshallow);
+	if (opt_update_shallow)
+		argv_array_push(&args, opt_update_shallow);
+	if (opt_refmap)
+		argv_array_push(&args, opt_refmap);
+
+	if (repo) {
+		argv_array_push(&args, repo);
+		argv_array_pushv(&args, refspecs);
+	} else if (*refspecs)
+		die("BUG: refspecs without repo?");
+	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
+	argv_array_clear(&args);
+	return ret;
+}
+
+/**
+ * "Pulls into void" by branching off merge_head.
+ */
+static int pull_into_void(const unsigned char *merge_head,
+		const unsigned char *curr_head)
+{
+	/*
+	 * Two-way merge: we treat the index as based on an empty tree,
+	 * and try to fast-forward to HEAD. This ensures we will not lose
+	 * index/worktree changes that the user already made on the unborn
+	 * branch.
+	 */
+	if (checkout_fast_forward(EMPTY_TREE_SHA1_BIN, merge_head, 0))
+		return 1;
+
+	if (update_ref("initial pull", "HEAD", merge_head, curr_head, 0, UPDATE_REFS_DIE_ON_ERR))
+		return 1;
+
+	return 0;
+}
+
+/**
+ * Runs git-merge, returning its exit status.
+ */
+static int run_merge(void)
+{
+	int ret;
+	struct argv_array args = ARGV_ARRAY_INIT;
+
+	argv_array_pushl(&args, "merge", NULL);
+
+	/* Shared options */
+	argv_push_verbosity(&args);
+	if (opt_progress)
+		argv_array_push(&args, opt_progress);
+
+	/* Options passed to git-merge */
+	if (opt_diffstat)
+		argv_array_push(&args, opt_diffstat);
+	if (opt_log)
+		argv_array_push(&args, opt_log);
+	if (opt_squash)
+		argv_array_push(&args, opt_squash);
+	if (opt_commit)
+		argv_array_push(&args, opt_commit);
+	if (opt_edit)
+		argv_array_push(&args, opt_edit);
+	if (opt_ff)
+		argv_array_push(&args, opt_ff);
+	if (opt_verify_signatures)
+		argv_array_push(&args, opt_verify_signatures);
+	argv_array_pushv(&args, opt_strategies.argv);
+	argv_array_pushv(&args, opt_strategy_opts.argv);
+	if (opt_gpg_sign)
+		argv_array_push(&args, opt_gpg_sign);
+
+	argv_array_push(&args, "FETCH_HEAD");
+	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
+	argv_array_clear(&args);
+	return ret;
+}
+
+/**
+ * Returns remote's upstream branch for the current branch. If remote is NULL,
+ * the current branch's configured default remote is used. Returns NULL if
+ * `remote` does not name a valid remote, HEAD does not point to a branch,
+ * remote is not the branch's configured remote or the branch does not have any
+ * configured upstream branch.
+ */
+static const char *get_upstream_branch(const char *remote)
+{
+	struct remote *rm;
+	struct branch *curr_branch;
+	const char *curr_branch_remote;
+
+	rm = remote_get(remote);
+	if (!rm)
+		return NULL;
+
+	curr_branch = branch_get("HEAD");
+	if (!curr_branch)
+		return NULL;
+
+	curr_branch_remote = remote_for_branch(curr_branch, NULL);
+	assert(curr_branch_remote);
+
+	if (strcmp(curr_branch_remote, rm->name))
+		return NULL;
+
+	return branch_get_upstream(curr_branch, NULL);
+}
+
+/**
+ * Derives the remote tracking branch from the remote and refspec.
+ *
+ * FIXME: The current implementation assumes the default mapping of
+ * refs/heads/<branch_name> to refs/remotes/<remote_name>/<branch_name>.
+ */
+static const char *get_tracking_branch(const char *remote, const char *refspec)
+{
+	struct refspec *spec;
+	const char *spec_src;
+	const char *merge_branch;
+
+	spec = parse_fetch_refspec(1, &refspec);
+	spec_src = spec->src;
+	if (!*spec_src || !strcmp(spec_src, "HEAD"))
+		spec_src = "HEAD";
+	else if (skip_prefix(spec_src, "heads/", &spec_src))
+		;
+	else if (skip_prefix(spec_src, "refs/heads/", &spec_src))
+		;
+	else if (starts_with(spec_src, "refs/") ||
+		starts_with(spec_src, "tags/") ||
+		starts_with(spec_src, "remotes/"))
+		spec_src = "";
+
+	if (*spec_src) {
+		if (!strcmp(remote, "."))
+			merge_branch = mkpath("refs/heads/%s", spec_src);
+		else
+			merge_branch = mkpath("refs/remotes/%s/%s", remote, spec_src);
+	} else
+		merge_branch = NULL;
+
+	free_refspec(1, spec);
+	return merge_branch;
+}
+
+/**
+ * Given the repo and refspecs, sets fork_point to the point at which the
+ * current branch forked from its remote tracking branch. Returns 0 on success,
+ * -1 on failure.
+ */
+static int get_rebase_fork_point(unsigned char *fork_point, const char *repo,
+		const char *refspec)
+{
+	int ret;
+	struct branch *curr_branch;
+	const char *remote_branch;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf sb = STRBUF_INIT;
+
+	curr_branch = branch_get("HEAD");
+	if (!curr_branch)
+		return -1;
+
+	if (refspec)
+		remote_branch = get_tracking_branch(repo, refspec);
+	else
+		remote_branch = get_upstream_branch(repo);
+
+	if (!remote_branch)
+		return -1;
+
+	argv_array_pushl(&cp.args, "merge-base", "--fork-point",
+			remote_branch, curr_branch->name, NULL);
+	cp.no_stdin = 1;
+	cp.no_stderr = 1;
+	cp.git_cmd = 1;
+
+	ret = capture_command(&cp, &sb, GIT_SHA1_HEXSZ);
+	if (ret)
+		goto cleanup;
+
+	ret = get_sha1_hex(sb.buf, fork_point);
+	if (ret)
+		goto cleanup;
+
+cleanup:
+	strbuf_release(&sb);
+	return ret ? -1 : 0;
+}
+
+/**
+ * Sets merge_base to the octopus merge base of curr_head, merge_head and
+ * fork_point. Returns 0 if a merge base is found, 1 otherwise.
+ */
+static int get_octopus_merge_base(unsigned char *merge_base,
+		const unsigned char *curr_head,
+		const unsigned char *merge_head,
+		const unsigned char *fork_point)
+{
+	struct commit_list *revs = NULL, *result;
+
+	commit_list_insert(lookup_commit_reference(curr_head), &revs);
+	commit_list_insert(lookup_commit_reference(merge_head), &revs);
+	if (!is_null_sha1(fork_point))
+		commit_list_insert(lookup_commit_reference(fork_point), &revs);
+
+	result = reduce_heads(get_octopus_merge_bases(revs));
+	free_commit_list(revs);
+	if (!result)
+		return 1;
+
+	hashcpy(merge_base, result->item->object.sha1);
+	return 0;
+}
+
+/**
+ * Given the current HEAD SHA1, the merge head returned from git-fetch and the
+ * fork point calculated by get_rebase_fork_point(), runs git-rebase with the
+ * appropriate arguments and returns its exit status.
+ */
+static int run_rebase(const unsigned char *curr_head,
+		const unsigned char *merge_head,
+		const unsigned char *fork_point)
+{
+	int ret;
+	unsigned char oct_merge_base[GIT_SHA1_RAWSZ];
+	struct argv_array args = ARGV_ARRAY_INIT;
+
+	if (!get_octopus_merge_base(oct_merge_base, curr_head, merge_head, fork_point))
+		if (!is_null_sha1(fork_point) && !hashcmp(oct_merge_base, fork_point))
+			fork_point = NULL;
+
+	argv_array_push(&args, "rebase");
+
+	/* Shared options */
+	argv_push_verbosity(&args);
+
+	/* Options passed to git-rebase */
+	if (opt_rebase == REBASE_PRESERVE)
+		argv_array_push(&args, "--preserve-merges");
+	if (opt_diffstat)
+		argv_array_push(&args, opt_diffstat);
+	argv_array_pushv(&args, opt_strategies.argv);
+	argv_array_pushv(&args, opt_strategy_opts.argv);
+	if (opt_gpg_sign)
+		argv_array_push(&args, opt_gpg_sign);
+
+	argv_array_push(&args, "--onto");
+	argv_array_push(&args, sha1_to_hex(merge_head));
+
+	if (fork_point && !is_null_sha1(fork_point))
+		argv_array_push(&args, sha1_to_hex(fork_point));
+	else
+		argv_array_push(&args, sha1_to_hex(merge_head));
+
+	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
+	argv_array_clear(&args);
+	return ret;
+}
+
+int cmd_pull(int argc, const char **argv, const char *prefix)
+{
+	const char *repo, **refspecs;
+	struct sha1_array merge_heads = SHA1_ARRAY_INIT;
+	unsigned char orig_head[GIT_SHA1_RAWSZ], curr_head[GIT_SHA1_RAWSZ];
+	unsigned char rebase_fork_point[GIT_SHA1_RAWSZ];
+
+	if (!getenv("GIT_REFLOG_ACTION"))
+		set_reflog_message(argc, argv);
+
+	argc = parse_options(argc, argv, prefix, pull_options, pull_usage, 0);
+
+	parse_repo_refspecs(argc, argv, &repo, &refspecs);
+
+	if (!opt_ff)
+		opt_ff = xstrdup_or_null(config_get_ff());
+
+	if (opt_rebase < 0)
+		opt_rebase = config_get_rebase();
+
+	git_config(git_default_config, NULL);
+
+	if (read_cache_unmerged())
+		die_resolve_conflict("Pull");
+
+	if (file_exists(git_path("MERGE_HEAD")))
+		die_conclude_merge();
+
+	if (get_sha1("HEAD", orig_head))
+		hashclr(orig_head);
+
+	if (opt_rebase) {
+		if (is_null_sha1(orig_head) && !is_cache_unborn())
+			die(_("Updating an unborn branch with changes added to the index."));
+
+		die_on_unclean_work_tree(prefix);
+
+		if (get_rebase_fork_point(rebase_fork_point, repo, *refspecs))
+			hashclr(rebase_fork_point);
+	}
+
+	if (run_fetch(repo, refspecs))
+		return 1;
+
+	if (opt_dry_run)
+		return 0;
+
+	if (get_sha1("HEAD", curr_head))
+		hashclr(curr_head);
+
+	if (!is_null_sha1(orig_head) && !is_null_sha1(curr_head) &&
+			hashcmp(orig_head, curr_head)) {
+		/*
+		 * The fetch involved updating the current branch.
+		 *
+		 * The working tree and the index file are still based on
+		 * orig_head commit, but we are merging into curr_head.
+		 * Update the working tree to match curr_head.
+		 */
+
+		warning(_("fetch updated the current branch head.\n"
+			"fast-forwarding your working tree from\n"
+			"commit %s."), sha1_to_hex(orig_head));
+
+		if (checkout_fast_forward(orig_head, curr_head, 0))
+			die(_("Cannot fast-forward your working tree.\n"
+				"After making sure that you saved anything precious from\n"
+				"$ git diff %s\n"
+				"output, run\n"
+				"$ git reset --hard\n"
+				"to recover."), sha1_to_hex(orig_head));
+	}
+
+	get_merge_heads(&merge_heads);
+
+	if (!merge_heads.nr)
+		die_no_merge_candidates(repo, refspecs);
+
+	if (is_null_sha1(orig_head)) {
+		if (merge_heads.nr > 1)
+			die(_("Cannot merge multiple branches into empty head."));
+		return pull_into_void(*merge_heads.sha1, curr_head);
+	} else if (opt_rebase) {
+		if (merge_heads.nr > 1)
+			die(_("Cannot rebase onto multiple branches."));
+		return run_rebase(curr_head, *merge_heads.sha1, rebase_fork_point);
+	} else
+		return run_merge();
+}
diff --git a/git-pull.sh b/contrib/examples/git-pull.sh
index a814bf61aa..a814bf61aa 100755
--- a/git-pull.sh
+++ b/contrib/examples/git-pull.sh
diff --git a/git.c b/git.c
index fe94066aee..55c327c7b3 100644
--- a/git.c
+++ b/git.c
@@ -445,6 +445,7 @@ static struct cmd_struct commands[] = {
 	{ "pickaxe", cmd_blame, RUN_SETUP },
 	{ "prune", cmd_prune, RUN_SETUP },
 	{ "prune-packed", cmd_prune_packed, RUN_SETUP },
+	{ "pull", cmd_pull, RUN_SETUP | NEED_WORK_TREE },
 	{ "push", cmd_push, RUN_SETUP },
 	{ "read-tree", cmd_read_tree, RUN_SETUP },
 	{ "receive-pack", cmd_receive_pack },
diff --git a/parse-options-cb.c b/parse-options-cb.c
index be8c413cfe..5ab6ed6b08 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -4,6 +4,7 @@
 #include "commit.h"
 #include "color.h"
 #include "string-list.h"
+#include "argv-array.h"
 
 /*----- some often used options -----*/
 
@@ -134,3 +135,71 @@ int parse_opt_noop_cb(const struct option *opt, const char *arg, int unset)
 {
 	return 0;
 }
+
+/**
+ * Recreates the command-line option in the strbuf.
+ */
+static int recreate_opt(struct strbuf *sb, const struct option *opt,
+		const char *arg, int unset)
+{
+	strbuf_reset(sb);
+
+	if (opt->long_name) {
+		strbuf_addstr(sb, unset ? "--no-" : "--");
+		strbuf_addstr(sb, opt->long_name);
+		if (arg) {
+			strbuf_addch(sb, '=');
+			strbuf_addstr(sb, arg);
+		}
+	} else if (opt->short_name && !unset) {
+		strbuf_addch(sb, '-');
+		strbuf_addch(sb, opt->short_name);
+		if (arg)
+			strbuf_addstr(sb, arg);
+	} else
+		return -1;
+
+	return 0;
+}
+
+/**
+ * For an option opt, recreates the command-line option in opt->value which
+ * must be an char* initialized to NULL. This is useful when we need to pass
+ * the command-line option to another command. Since any previous value will be
+ * overwritten, this callback should only be used for options where the last
+ * one wins.
+ */
+int parse_opt_passthru(const struct option *opt, const char *arg, int unset)
+{
+	static struct strbuf sb = STRBUF_INIT;
+	char **opt_value = opt->value;
+
+	if (recreate_opt(&sb, opt, arg, unset) < 0)
+		return -1;
+
+	if (*opt_value)
+		free(*opt_value);
+
+	*opt_value = strbuf_detach(&sb, NULL);
+
+	return 0;
+}
+
+/**
+ * For an option opt, recreate the command-line option, appending it to
+ * opt->value which must be a argv_array. This is useful when we need to pass
+ * the command-line option, which can be specified multiple times, to another
+ * command.
+ */
+int parse_opt_passthru_argv(const struct option *opt, const char *arg, int unset)
+{
+	static struct strbuf sb = STRBUF_INIT;
+	struct argv_array *opt_value = opt->value;
+
+	if (recreate_opt(&sb, opt, arg, unset) < 0)
+		return -1;
+
+	argv_array_push(opt_value, sb.buf);
+
+	return 0;
+}
diff --git a/parse-options.h b/parse-options.h
index ca865f66d7..6ca8388a53 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -227,6 +227,8 @@ extern int parse_opt_with_commit(const struct option *, const char *, int);
 extern int parse_opt_tertiary(const struct option *, const char *, int);
 extern int parse_opt_string_list(const struct option *, const char *, int);
 extern int parse_opt_noop_cb(const struct option *, const char *, int);
+extern int parse_opt_passthru(const struct option *, const char *, int);
+extern int parse_opt_passthru_argv(const struct option *, const char *, int);
 
 #define OPT__VERBOSE(var, h)  OPT_COUNTUP('v', "verbose", (var), (h))
 #define OPT__QUIET(var, h)    OPT_COUNTUP('q', "quiet",   (var), (h))
@@ -245,5 +247,9 @@ extern int parse_opt_noop_cb(const struct option *, const char *, int);
 	OPT_COLOR_FLAG(0, "color", (var), (h))
 #define OPT_COLUMN(s, l, v, h) \
 	{ OPTION_CALLBACK, (s), (l), (v), N_("style"), (h), PARSE_OPT_OPTARG, parseopt_column_callback }
+#define OPT_PASSTHRU(s, l, v, a, h, f) \
+	{ OPTION_CALLBACK, (s), (l), (v), (a), (h), (f), parse_opt_passthru }
+#define OPT_PASSTHRU_ARGV(s, l, v, a, h, f) \
+	{ OPTION_CALLBACK, (s), (l), (v), (a), (h), (f), parse_opt_passthru_argv }
 
 #endif