[RFC PATCH 00/35] git update: fix broken git pull

@@ -1620,7 +1620,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	}
 
 	if (fast_forward == FF_ONLY)
-		die(_("Not possible to fast-forward, aborting."));
+		die(_("unable to fast-forward"));
 
 	if (autostash)
 		create_autostash(the_repository,

@@ -1259,7 +1259,8 @@ static int merging_a_throwaway_tag(struct commit *commit)
 	return is_throwaway_tag;
 }
 
-int cmd_merge(int argc, const char **argv, const char *prefix)
+static int merge_common(int argc, const char **argv, const char *prefix,
+	const struct option *options, const char * const usage[])
 {
 	struct object_id result_tree, stash, head_oid;
 	struct commit *head_commit;

@@ -1273,7 +1274,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	int orig_argc = argc;
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
-		usage_with_options(builtin_merge_usage, builtin_merge_options);
+		usage_with_options(usage, options);
 
 	/*
 	 * Check if we are _not_ on a detached HEAD, i.e. if there is a

@@ -1299,8 +1300,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 	if (branch_mergeoptions)
 		parse_branch_merge_options(branch_mergeoptions);
-	argc = parse_options(argc, argv, prefix, builtin_merge_options,
-			builtin_merge_usage, 0);
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
 	if (shortlog_len < 0)
 		shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;
 

@@ -1314,7 +1314,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 		if (orig_argc != 2)
 			usage_msg_opt(_("--abort expects no arguments"),
-			      builtin_merge_usage, builtin_merge_options);
+				usage, options);
 
 		if (!file_exists(git_path_merge_head(the_repository)))
 			die(_("There is no merge to abort (MERGE_HEAD missing)."));

@@ -1336,8 +1336,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	if (quit_current_merge) {
 		if (orig_argc != 2)
 			usage_msg_opt(_("--quit expects no arguments"),
-				      builtin_merge_usage,
-				      builtin_merge_options);
+				usage, options);
 
 		remove_merge_branch_state(the_repository);
 		goto done;

@@ -1349,7 +1348,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 		if (orig_argc != 2)
 			usage_msg_opt(_("--continue expects no arguments"),
-			      builtin_merge_usage, builtin_merge_options);
+				usage, options);
 
 		if (!file_exists(git_path_merge_head(the_repository)))
 			die(_("There is no merge in progress (MERGE_HEAD missing)."));

@@ -1416,8 +1415,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	}
 
 	if (!argc)
-		usage_with_options(builtin_merge_usage,
-			builtin_merge_options);
+		usage_with_options(usage, options);
 
 	if (!head_commit) {
 		/*

@@ -1458,8 +1456,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 				      argc, argv, &merge_msg);
 
 	if (!head_commit || !argc)
-		usage_with_options(builtin_merge_usage,
-			builtin_merge_options);
+		usage_with_options(usage, options);
 
 	if (verify_signatures) {
 		for (p = remoteheads; p; p = p->next) {

@@ -1738,3 +1735,8 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	free(branch_to_free);
 	return ret;
 }
+
+int cmd_merge(int argc, const char **argv, const char *prefix)
+{
+	return merge_common(argc, argv, prefix, builtin_merge_options, builtin_merge_usage);
+}

@@ -62,6 +62,7 @@
 /git-describe
 /git-env--helper
 /git-fast-export
+/git-fast-forward
 /git-fast-import
 /git-fetch
 /git-fetch-pack

@@ -0,0 +1,26 @@
+git-fast-forward(1)
+===================
+
+NAME
+----
+git-fast-forward - Advance the branch pointer
+
+SYNOPSIS
+--------
+[verse]
+'git fast-forward' [<commit>]
+
+DESCRIPTION
+-----------
+Incorporates changes into the current branch. By default the upstream branch is
+used, but a different commit can be specified in the arguments.
+
+THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOUR MAY CHANGE.
+
+SEE ALSO
+--------
+linkgit:git-merge[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite

@@ -772,6 +772,7 @@ BUILT_INS += $(patsubst builtin/%.o,git-%$X,$(BUILTIN_OBJS))
 
 BUILT_INS += git-cherry$X
 BUILT_INS += git-cherry-pick$X
+BUILT_INS += git-fast-forward$X
 BUILT_INS += git-format-patch$X
 BUILT_INS += git-fsck-objects$X
 BUILT_INS += git-init$X

@@ -151,6 +151,7 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix);
 int cmd_difftool(int argc, const char **argv, const char *prefix);
 int cmd_env__helper(int argc, const char **argv, const char *prefix);
 int cmd_fast_export(int argc, const char **argv, const char *prefix);
+int cmd_fast_forward(int argc, const char **argv, const char *prefix);
 int cmd_fast_import(int argc, const char **argv, const char *prefix);
 int cmd_fetch(int argc, const char **argv, const char *prefix);
 int cmd_fetch_pack(int argc, const char **argv, const char *prefix);

@@ -61,6 +61,11 @@ static const char * const builtin_merge_usage[] = {
 	NULL
 };
 
+static const char * const builtin_ff_usage[] = {
+	N_("git fast-forward [<commit>]"),
+	NULL
+};
+
 static int show_diffstat = 1, shortlog_len = -1, squash;
 static int option_commit = -1;
 static int option_edit = -1;

@@ -304,6 +309,10 @@ static struct option builtin_merge_options[] = {
 	OPT_END()
 };
 
+static struct option builtin_ff_options[] = {
+	OPT_END()
+};
+
 static int save_state(struct object_id *stash)
 {
 	int len;

@@ -1740,3 +1749,9 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 {
 	return merge_common(argc, argv, prefix, builtin_merge_options, builtin_merge_usage);
 }
+
+int cmd_fast_forward(int argc, const char **argv, const char *prefix)
+{
+	fast_forward = FF_ONLY;
+	return merge_common(argc, argv, prefix, builtin_ff_options, builtin_ff_usage);
+}

@@ -1786,6 +1786,16 @@ _git_difftool ()
 	__git_complete_revlist_file
 }
 
+_git_fast_forward ()
+{
+	case "$cur" in
+	--*)
+		__gitcomp_builtin fast-forward
+		return
+	esac
+	__git_complete_refs
+}
+
 __git_fetch_recurse_submodules="yes on-demand no"
 
 _git_fetch ()

@@ -524,6 +524,7 @@ static struct cmd_struct commands[] = {
 	{ "difftool", cmd_difftool, RUN_SETUP_GENTLY },
 	{ "env--helper", cmd_env__helper },
 	{ "fast-export", cmd_fast_export, RUN_SETUP },
+	{ "fast-forward", cmd_fast_forward, RUN_SETUP | NEED_WORK_TREE },
 	{ "fast-import", cmd_fast_import, RUN_SETUP | NO_PARSEOPT },
 	{ "fetch", cmd_fetch, RUN_SETUP },
 	{ "fetch-pack", cmd_fetch_pack, RUN_SETUP | NO_PARSEOPT },

@@ -205,6 +205,16 @@ test_expect_success 'merge c0 with c1 with --ff-only' '
 
 test_debug 'git log --graph --decorate --oneline --all'
 
+test_expect_success 'fast-forward c0 with c1' '
+	git reset --hard c0 &&
+	git fast-forward c1 &&
+	git fast-forward HEAD c0 c1 &&
+	verify_merge file result.1 &&
+	verify_head "$c1"
+'
+
+test_debug 'git log --graph --decorate --oneline --all'
+
 test_expect_success 'merge from unborn branch' '
 	git checkout -f main &&
 	test_might_fail git branch -D kid &&

@@ -322,6 +332,17 @@ test_expect_success 'merges with --ff-only' '
 	verify_head $c3
 '
 
+test_expect_success 'fast-forward' '
+	git reset --hard c1 &&
+	test_tick &&
+	test_must_fail git fast-forward c2 &&
+	test_must_fail git fast-forward c3 &&
+	test_must_fail git fast-forward c2 c3 &&
+	git reset --hard c0 &&
+	git merge c3 &&
+	verify_head $c3
+'
+
 test_expect_success 'merges with merge.ff=only' '
 	git reset --hard c1 &&
 	test_tick &&

@@ -15,11 +15,41 @@ DESCRIPTION
 Incorporates changes into the current branch. By default the upstream branch is
 used, but a different commit can be specified in the arguments.
 
+Assume the following history exists and the current branch is
+`master`:
+
+------------
+    D---C---B---A origin/master
+	^
+	|
+      master
+------------
+
+Then `git fast-forward` will advance the local `master` to `origin/master`:
+
+------------
+    D---C---B---A master, origin/master
+------------
+
+This operation is not always possible; if you made changes and the branches
+have diverged:
+
+------------
+    D---C---B---A origin/master
+	 \
+	  X---Y master
+------------
+
+then the fast-forward command will fail.
+
+In those cases you need to either `git merge`, or `git rebase` in order to
+synchronize the two branches.
+
 THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOUR MAY CHANGE.
 
 SEE ALSO
 --------
-linkgit:git-merge[1]
+linkgit:git-merge[1], linkgit:git-rebase[1]
 
 GIT
 ---

@@ -326,3 +326,14 @@ void detach_advice(const char *new_name)
 
 	fprintf(stderr, fmt, new_name);
 }
+
+void diverging_advice(void)
+{
+	advise(_("Diverging branches can't be fast-forwarded, you need to either:\n"
+		"\n"
+		"\tgit merge\n"
+		"\n"
+		"or:\n"
+		"\n"
+		"\tgit rebase\n"));
+}

@@ -97,5 +97,6 @@ void NORETURN die_resolve_conflict(const char *me);
 void NORETURN die_conclude_merge(void);
 void advise_on_updating_sparse_paths(struct string_list *pathspec_list);
 void detach_advice(const char *new_name);
+void diverging_advice(void);
 
 #endif /* ADVICE_H */

@@ -1625,8 +1625,10 @@ static int merge_common(int argc, const char **argv, const char *prefix,
 		}
 	}
 
-	if (fast_forward == FF_ONLY)
+	if (fast_forward == FF_ONLY) {
+		diverging_advice();
 		die(_("unable to fast-forward"));
+	}
 
 	if (autostash)
 		create_autostash(the_repository,

@@ -123,4 +123,6 @@ advice.*::
 		Advice shown when either linkgit:git-add[1] or linkgit:git-rm[1]
 		is asked to update index entries outside the current sparse
 		checkout.
+	diverging::
+		Advice shown when a fast-forward is not possible.
 --

@@ -110,6 +110,7 @@ static struct {
 	[ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME] 	= { "checkoutAmbiguousRemoteBranchName", 1 },
 	[ADVICE_COMMIT_BEFORE_MERGE]			= { "commitBeforeMerge", 1 },
 	[ADVICE_DETACHED_HEAD]				= { "detachedHead", 1 },
+	[ADVICE_DIVERGING]				= { "diverging", 1 },
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates", 1 },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated", 1 },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook", 1 },

@@ -329,7 +330,8 @@ void detach_advice(const char *new_name)
 
 void diverging_advice(void)
 {
-	advise(_("Diverging branches can't be fast-forwarded, you need to either:\n"
+	advise_if_enabled(ADVICE_DIVERGING,
+		_("Diverging branches can't be fast-forwarded, you need to either:\n"
 		"\n"
 		"\tgit merge\n"
 		"\n"

@@ -49,6 +49,7 @@ extern int advice_add_empty_pathspec;
 	ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME,
 	ADVICE_COMMIT_BEFORE_MERGE,
 	ADVICE_DETACHED_HEAD,
+	ADVICE_DIVERGING,
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_GRAFT_FILE_DEPRECATED,
 	ADVICE_IGNORED_HOOK,

@@ -47,6 +47,54 @@ synchronize the two branches.
 
 THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOUR MAY CHANGE.
 
+MERGE OR REBASE
+---------------
+
+The decision to whether merge or rebase depends on the situation, and the
+project. Traditionally git has prefered merge over rebase, but that creates a
+new commit, and that's frowned up on some projects, so you can't just simply
+choose to merge blindly.
+
+------------
+    D---C---B---A origin/master
+	 \
+	  X---Y master
+------------
+
+The nature of distributed version control systems make this divergence
+unavoidable. You must decide how to synchronize this divergence.
+
+If you choose to merge, the two heads (master and origin/master) will be joined
+together in a new commit:
+
+------------
+	  origin/master
+		|
+		v
+    D---C---B---A---M master
+	 \	   /
+	  X---Y---+
+------------
+
+This new commit is called a merge commit and has two parents (A and Y).
+
+Rebasing on the other hand rewrites the history:
+
+------------
+	  origin/master
+		|
+		v
+    D---C---B---A---X'---Y' master
+------------
+
+The commits that diverged (X and Y) are rewritten as if they were created on top
+of the new base (A). This creates a linear history, which is cleaner, but some
+people prefer to preserve the original hsitory.
+
+In both cases it's likely you would have to resolve conflicts, the difference is
+that in a merge you would have to do it all at once in one commit, while with a
+rebase you would have to do it on every rewritten commit.
+
 SEE ALSO
 --------
 linkgit:git-merge[1], linkgit:git-rebase[1]

@@ -337,5 +337,7 @@ void diverging_advice(void)
 		"\n"
 		"or:\n"
 		"\n"
-		"\tgit rebase\n"));
+		"\tgit rebase\n"
+		"\n"
+		"For more information check \"git help fast-forward\".\n"));
 }

@@ -171,6 +171,7 @@
 /git-tag
 /git-unpack-file
 /git-unpack-objects
+/git-update
 /git-update-index
 /git-update-ref
 /git-update-server-info

@@ -440,6 +440,8 @@ include::config/rerere.txt[]
 
 include::config/reset.txt[]
 
+include::config/update.txt[]
+
 include::config/sendemail.txt[]
 
 include::config/sequencer.txt[]

@@ -0,0 +1,32 @@
+git-update(1)
+=============
+
+NAME
+----
+git-update - Update the current branch to the latest remote
+
+SYNOPSIS
+--------
+[verse]
+'git update'
+
+DESCRIPTION
+-----------
+
+Incorporates changes from a remote repository into the current branch.
+
+`git update` runs `git fetch` and then tries to advance the current branch to
+the remote branch with `git fast-forward`. If you don't have any extra changes
+the update operation is straight-forward, but if you do a further `git merge` or
+`git rebase` will be needed.
+
+THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOUR MAY CHANGE.
+
+SEE ALSO
+--------
+linkgit:git-fetch[1], linkgit:git-fast-forward[1],
+linkgit:git-merge[1], linkgit:git-rebase[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite

@@ -1161,6 +1161,7 @@ BUILTIN_OBJS += builtin/symbolic-ref.o
 BUILTIN_OBJS += builtin/tag.o
 BUILTIN_OBJS += builtin/unpack-file.o
 BUILTIN_OBJS += builtin/unpack-objects.o
+BUILTIN_OBJS += builtin/update.o
 BUILTIN_OBJS += builtin/update-index.o
 BUILTIN_OBJS += builtin/update-ref.o
 BUILTIN_OBJS += builtin/update-server-info.o

@@ -229,6 +229,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix);
 int cmd_tar_tree(int argc, const char **argv, const char *prefix);
 int cmd_unpack_file(int argc, const char **argv, const char *prefix);
 int cmd_unpack_objects(int argc, const char **argv, const char *prefix);
+int cmd_update(int argc, const char **argv, const char *prefix);
 int cmd_update_index(int argc, const char **argv, const char *prefix);
 int cmd_update_ref(int argc, const char **argv, const char *prefix);
 int cmd_update_server_info(int argc, const char **argv, const char *prefix);

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2021 Felipe Contreras
+ */
+
+#include "builtin.h"
+#include "run-command.h"
+#include "dir.h"
+
+static int run_fetch(void)
+{
+	struct strvec args = STRVEC_INIT;
+	int ret;
+
+	strvec_pushl(&args, "fetch", "--update-head-ok", NULL);
+
+	ret = run_command_v_opt(args.v, RUN_GIT_CMD);
+	strvec_clear(&args);
+	return ret;
+}
+
+static int run_fast_forward(void)
+{
+	struct strvec args = STRVEC_INIT;
+	int ret;
+
+	strvec_pushl(&args, "fast-forward", "FETCH_HEAD", NULL);
+
+	ret = run_command_v_opt(args.v, RUN_GIT_CMD);
+	strvec_clear(&args);
+	return ret;
+}
+
+int cmd_update(int argc, const char **argv, const char *prefix)
+{
+	if (!getenv("GIT_REFLOG_ACTION"))
+		setenv("GIT_REFLOG_ACTION", "update", 0);
+
+	if (repo_read_index_unmerged(the_repository))
+		die_resolve_conflict("update");
+
+	if (file_exists(git_path_merge_head(the_repository)))
+		die_conclude_merge();
+
+	if (run_fetch())
+		return 1;
+
+	return run_fast_forward();
+}

@@ -3257,6 +3257,18 @@ _git_tag ()
 	esac
 }
 
+_git_update ()
+{
+	case "$cur" in
+	--*)
+		__gitcomp_builtin update
+
+		return
+		;;
+	esac
+	__git_complete_remote_or_refspec
+}
+
 _git_whatchanged ()
 {
 	_git_log

@@ -610,6 +610,7 @@ static struct cmd_struct commands[] = {
 	{ "tag", cmd_tag, RUN_SETUP | DELAY_PAGER_CONFIG },
 	{ "unpack-file", cmd_unpack_file, RUN_SETUP | NO_PARSEOPT },
 	{ "unpack-objects", cmd_unpack_objects, RUN_SETUP | NO_PARSEOPT },
+	{ "update", cmd_update, RUN_SETUP | NEED_WORK_TREE },
 	{ "update-index", cmd_update_index, RUN_SETUP },
 	{ "update-ref", cmd_update_ref, RUN_SETUP },
 	{ "update-server-info", cmd_update_server_info, RUN_SETUP },

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+test_description='update'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo one > file &&
+	git add file &&
+	git commit -a -m one &&
+	echo two > file &&
+	git commit -a -m two
+'
+
+test_expect_success 'basic update' '
+	test_when_finished "rm -rf test" &&
+	(
+	git clone . test &&
+	cd test &&
+	git reset --hard @^ &&
+	git update &&
+	test_cmp_rev master origin/master
+	)
+'
+
+test_expect_success 'non-fast-forward update' '
+	test_when_finished "rm -rf test" &&
+	(
+	git clone . test &&
+	cd test &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	test_must_fail git update &&
+	test_cmp_rev @ master
+	)
+'
+
+test_done

@@ -3,9 +3,19 @@
  */
 
 #include "builtin.h"
+#include "parse-options.h"
 #include "run-command.h"
 #include "dir.h"
 
+static const char * const update_usage[] = {
+	N_("git update"),
+	NULL
+};
+
+static struct option update_options[] = {
+	OPT_END()
+};
+
 static int run_fetch(void)
 {
 	struct strvec args = STRVEC_INIT;

@@ -35,6 +45,8 @@ int cmd_update(int argc, const char **argv, const char *prefix)
 	if (!getenv("GIT_REFLOG_ACTION"))
 		setenv("GIT_REFLOG_ACTION", "update", 0);
 
+	argc = parse_options(argc, argv, prefix, update_options, update_usage, 0);
+
 	if (repo_read_index_unmerged(the_repository))
 		die_resolve_conflict("update");
 

@@ -8,7 +8,7 @@ git-update - Update the current branch to the latest remote
 SYNOPSIS
 --------
 [verse]
-'git update'
+'git update' [<options>]
 
 DESCRIPTION
 -----------

@@ -22,6 +22,13 @@ the update operation is straight-forward, but if you do a further `git merge` or
 
 THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOUR MAY CHANGE.
 
+OPTIONS
+-------
+
+-f::
+--ff::
+	Forces a fast-forward.
+
 SEE ALSO
 --------
 linkgit:git-fetch[1], linkgit:git-fast-forward[1],

@@ -7,12 +7,22 @@
 #include "run-command.h"
 #include "dir.h"
 
+enum update_mode_type {
+	UPDATE_MODE_FAST_FORWARD = 0
+};
+
+static enum update_mode_type mode = UPDATE_MODE_FAST_FORWARD;
+
 static const char * const update_usage[] = {
-	N_("git update"),
+	N_("git update [<options>]"),
 	NULL
 };
 
 static struct option update_options[] = {
+	OPT_SET_INT_F('f', "ff", &mode,
+		N_("incorporate changes by fast-forwarding"),
+		UPDATE_MODE_FAST_FORWARD, PARSE_OPT_NONEG),
+
 	OPT_END()
 };
 

@@ -56,5 +66,8 @@ int cmd_update(int argc, const char **argv, const char *prefix)
 	if (run_fetch())
 		return 1;
 
-	return run_fast_forward();
+	if (mode == UPDATE_MODE_FAST_FORWARD)
+		return run_fast_forward();
+
+	return 1;
 }

@@ -29,6 +29,10 @@ OPTIONS
 --ff::
 	Forces a fast-forward.
 
+-m::
+--merge::
+	Forces a merge.
+
 SEE ALSO
 --------
 linkgit:git-fetch[1], linkgit:git-fast-forward[1],

@@ -8,7 +8,8 @@
 #include "dir.h"
 
 enum update_mode_type {
-	UPDATE_MODE_FAST_FORWARD = 0
+	UPDATE_MODE_FAST_FORWARD = 0,
+	UPDATE_MODE_MERGE
 };
 
 static enum update_mode_type mode = UPDATE_MODE_FAST_FORWARD;

@@ -22,6 +23,9 @@ static struct option update_options[] = {
 	OPT_SET_INT_F('f', "ff", &mode,
 		N_("incorporate changes by fast-forwarding"),
 		UPDATE_MODE_FAST_FORWARD, PARSE_OPT_NONEG),
+	OPT_SET_INT_F('m', "merge", &mode,
+		N_("incorporate changes by merging"),
+		UPDATE_MODE_MERGE, PARSE_OPT_NONEG),
 
 	OPT_END()
 };

@@ -50,6 +54,18 @@ static int run_fast_forward(void)
 	return ret;
 }
 
+static int run_merge(void)
+{
+	int ret;
+	struct strvec args = STRVEC_INIT;
+
+	strvec_pushl(&args, "merge", "FETCH_HEAD", NULL);
+
+	ret = run_command_v_opt(args.v, RUN_GIT_CMD);
+	strvec_clear(&args);
+	return ret;
+}
+
 int cmd_update(int argc, const char **argv, const char *prefix)
 {
 	if (!getenv("GIT_REFLOG_ACTION"))

@@ -68,6 +84,8 @@ int cmd_update(int argc, const char **argv, const char *prefix)
 
 	if (mode == UPDATE_MODE_FAST_FORWARD)
 		return run_fast_forward();
+	if (mode == UPDATE_MODE_MERGE)
+		return run_merge();
 
 	return 1;
 }

@@ -42,4 +42,19 @@ test_expect_success 'non-fast-forward update' '
 	)
 '
 
+test_expect_success 'git update non-fast-forward with merge' '
+	test_when_finished "rm -rf test" &&
+	(
+	git clone . test &&
+	cd test &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	git update --merge
+	)
+'
+
 test_done

@@ -1742,7 +1742,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		if (!stat(git_path_merge_mode(the_repository), &statbuf)) {
 			if (strbuf_read_file(&sb, git_path_merge_mode(the_repository), 0) < 0)
 				die_errno(_("could not read MERGE_MODE"));
-			if (!strcmp(sb.buf, "no-ff"))
+			if (strstr(sb.buf, "no-ff"))
 				allow_fast_forward = 0;
 		}
 		if (allow_fast_forward)

@@ -149,6 +149,10 @@ ifndef::git-pull[]
 	Note that not all merge strategies may support progress
 	reporting.
 
+--reverse-parents::
+--no-reverse-parents::
+	Reverse the order of parents in the merge commit.
+
 endif::git-pull[]
 
 --autostash::

@@ -1724,6 +1724,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		FILE *fp;
 		int allow_fast_forward = 1;
 		struct commit_list **pptr = &parents;
+		int reverse_parents = 0;
 
 		if (!reflog_msg)
 			reflog_msg = "commit (merge)";

@@ -1744,9 +1745,13 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 				die_errno(_("could not read MERGE_MODE"));
 			if (strstr(sb.buf, "no-ff"))
 				allow_fast_forward = 0;
+			if (strstr(sb.buf, "reverse"))
+				reverse_parents = 1;
 		}
 		if (allow_fast_forward)
 			reduce_heads_replace(&parents);
+		if (reverse_parents)
+			parents = reverse_commit_list(parents);
 	} else {
 		if (!reflog_msg)
 			reflog_msg = is_from_cherry_pick(whence)

@@ -91,6 +91,7 @@ static int signoff;
 static const char *sign_commit;
 static int autostash;
 static int no_verify;
+static int reverse_parents;
 
 static struct strategy all_strategy[] = {
 	{ "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },

@@ -306,6 +307,8 @@ static struct option builtin_merge_options[] = {
 	OPT_BOOL(0, "overwrite-ignore", &overwrite_ignore, N_("update ignored files (default)")),
 	OPT_BOOL(0, "signoff", &signoff, N_("add a Signed-off-by trailer")),
 	OPT_BOOL(0, "no-verify", &no_verify, N_("bypass pre-merge-commit and commit-msg hooks")),
+	OPT_BOOL(0, "reverse-parents", &reverse_parents,
+		N_("reverse the order of parents")),
 	OPT_END()
 };
 

@@ -913,6 +916,8 @@ static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 	pptr = commit_list_append(head, pptr);
 	pptr = commit_list_append(remoteheads->item, pptr);
 	prepare_to_commit(remoteheads);
+	if (reverse_parents)
+		parents = reverse_commit_list(parents);
 	if (commit_tree(merge_msg.buf, merge_msg.len, &result_tree, parents,
 			&result_commit, NULL, sign_commit))
 		die(_("failed to write commit object"));

@@ -937,6 +942,8 @@ static int finish_automerge(struct commit *head,
 	parents = remoteheads;
 	if (!head_subsumed || fast_forward == FF_NO)
 		commit_list_insert(head, &parents);
+	if (reverse_parents)
+		parents = reverse_commit_list(parents);
 	prepare_to_commit(remoteheads);
 	if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parents,
 			&result_commit, NULL, sign_commit))

@@ -1049,7 +1056,9 @@ static void write_merge_heads(struct commit_list *remoteheads)
 
 	strbuf_reset(&buf);
 	if (fast_forward == FF_NO)
-		strbuf_addstr(&buf, "no-ff");
+		strbuf_addstr(&buf, "no-ff ");
+	if (reverse_parents)
+		strbuf_addstr(&buf, "reverse ");
 	write_file_buf(git_path_merge_mode(the_repository), buf.buf, buf.len);
 	strbuf_release(&buf);
 }

@@ -563,6 +563,16 @@ test_expect_success 'merge c0 with c1 (no-ff)' '
 
 test_debug 'git log --graph --decorate --oneline --all'
 
+test_expect_success 'merge c0 with c1 (--reverse-parents)' '
+	git reset --hard c0 &&
+	test_tick &&
+	git merge --no-ff --reverse-parents c1 &&
+	verify_merge file result.1 &&
+	verify_parents $c1 $c0
+'
+
+test_debug 'git log --graph --decorate --oneline --all'
+
 test_expect_success 'merge c0 with c1 (merge.ff=false)' '
 	git reset --hard c0 &&
 	test_config merge.ff "false" &&

@@ -940,6 +950,22 @@ test_expect_success 'merge annotated/signed tag w/ tracking' '
 	)
 '
 
+test_expect_success 'merge --reverse-parents --no-commit && commit' '
+	git reset --hard c0 &&
+	git merge --no-ff --reverse-parents --no-commit c1 &&
+	EDITOR=: git commit &&
+	verify_parents $c1 $c0
+'
+
+test_debug 'git log --graph --decorate --oneline --all'
+
+test_expect_success 'amending reverse merge commit' '
+	EDITOR=: git commit --amend &&
+	verify_parents $c1 $c0
+'
+
+test_debug 'git log --graph --decorate --oneline --all'
+
 test_expect_success GPG 'merge --ff-only tag' '
 	git reset --hard c0 &&
 	git commit --allow-empty -m "A newer commit" &&

@@ -59,7 +59,7 @@ static int run_merge(void)
 	int ret;
 	struct strvec args = STRVEC_INIT;
 
-	strvec_pushl(&args, "merge", "FETCH_HEAD", NULL);
+	strvec_pushl(&args, "merge", "--reverse-parents", "FETCH_HEAD", NULL);
 
 	ret = run_command_v_opt(args.v, RUN_GIT_CMD);
 	strvec_clear(&args);

@@ -53,7 +53,9 @@ test_expect_success 'git update non-fast-forward with merge' '
 	git commit -m new &&
 	git checkout -b test -t other &&
 	git reset --hard master &&
-	git update --merge
+	git update --merge &&
+	test_cmp_rev @^2 master &&
+	test_cmp_rev @^1 other
 	)
 '
 

@@ -1136,6 +1136,7 @@ static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *mer
 	opts.add_title = !have_message;
 	opts.shortlog_len = shortlog_len;
 	opts.credit_people = (0 < option_edit);
+	opts.reverse_parents = reverse_parents;
 
 	fmt_merge_msg(merge_names, merge_msg, &opts);
 	if (merge_msg->len)

@@ -432,6 +432,19 @@ static int dest_suppressed(const char *dest_branch)
 	return 0;
 }
 
+static void fmt_update_msg_title(struct strbuf *out, const char *current_branch)
+{
+	struct src_data *src_data;
+	strbuf_addf(out, "Merge branch '%s'", current_branch);
+	src_data = srcs.items[0].util;
+	if (src_data->branch.nr) {
+		const char *branch_name = src_data->branch.items[0].string;
+		if (!dest_suppressed(branch_name))
+			strbuf_addf(out, " into %s", branch_name);
+	}
+	strbuf_addch(out, '\n');
+}
+
 static void fmt_merge_msg_title(struct strbuf *out,
 				const char *current_branch)
 {

@@ -665,8 +678,12 @@ int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
 			die("error in line %d: %.*s", i, len, p);
 	}
 
-	if (opts->add_title && srcs.nr)
-		fmt_merge_msg_title(out, current_branch);
+	if (opts->add_title && srcs.nr) {
+		if (opts->reverse_parents)
+			fmt_update_msg_title(out, current_branch);
+		else
+			fmt_merge_msg_title(out, current_branch);
+	}
 
 	if (origins.nr)
 		fmt_merge_msg_sigs(out);

@@ -7,7 +7,8 @@
 
 struct fmt_merge_msg_opts {
 	unsigned add_title:1,
-		credit_people:1;
+		credit_people:1,
+		reverse_parents:1;
 	int shortlog_len;
 };
 

@@ -7,6 +7,13 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
 
+check_msg () {
+	test "$2" != "master" && into=" into '$2'"
+	echo "Merge branch '$1'${into}" > expected
+	git log -1 --format=%s > actual &&
+	test_cmp expected actual
+}
+
 test_expect_success 'setup' '
 	echo one > file &&
 	git add file &&

@@ -55,7 +62,8 @@ test_expect_success 'git update non-fast-forward with merge' '
 	git reset --hard master &&
 	git update --merge &&
 	test_cmp_rev @^2 master &&
-	test_cmp_rev @^1 other
+	test_cmp_rev @^1 other &&
+	check_msg test other
 	)
 '
 

@@ -33,6 +33,10 @@ OPTIONS
 --merge::
 	Forces a merge.
 
+-r::
+--rebase::
+	Forces a rebase.
+
 SEE ALSO
 --------
 linkgit:git-fetch[1], linkgit:git-fast-forward[1],

@@ -9,7 +9,8 @@
 
 enum update_mode_type {
 	UPDATE_MODE_FAST_FORWARD = 0,
-	UPDATE_MODE_MERGE
+	UPDATE_MODE_MERGE,
+	UPDATE_MODE_REBASE
 };
 
 static enum update_mode_type mode = UPDATE_MODE_FAST_FORWARD;

@@ -26,6 +27,9 @@ static struct option update_options[] = {
 	OPT_SET_INT_F('m', "merge", &mode,
 		N_("incorporate changes by merging"),
 		UPDATE_MODE_MERGE, PARSE_OPT_NONEG),
+	OPT_SET_INT_F('r', "rebase", &mode,
+		N_("incorporate changes by rebasing"),
+		UPDATE_MODE_REBASE, PARSE_OPT_NONEG),
 
 	OPT_END()
 };

@@ -66,6 +70,18 @@ static int run_merge(void)
 	return ret;
 }
 
+static int run_rebase(void)
+{
+	int ret;
+	struct strvec args = STRVEC_INIT;
+
+	strvec_pushl(&args, "rebase", "FETCH_HEAD", NULL);
+
+	ret = run_command_v_opt(args.v, RUN_GIT_CMD);
+	strvec_clear(&args);
+	return ret;
+}
+
 int cmd_update(int argc, const char **argv, const char *prefix)
 {
 	if (!getenv("GIT_REFLOG_ACTION"))

@@ -86,6 +102,8 @@ int cmd_update(int argc, const char **argv, const char *prefix)
 		return run_fast_forward();
 	if (mode == UPDATE_MODE_MERGE)
 		return run_merge();
+	if (mode == UPDATE_MODE_REBASE)
+		return run_rebase();
 
 	return 1;
 }

@@ -67,4 +67,21 @@ test_expect_success 'git update non-fast-forward with merge' '
 	)
 '
 
+test_expect_success 'git update non-fast-forward with rebase' '
+	test_when_finished "rm -rf test" &&
+	(
+	git clone . test &&
+	cd test &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	git update --rebase &&
+	test_cmp_rev @^ other &&
+	test_must_fail git rev-parse --verify -q @^2
+	)
+'
+
 test_done

@@ -466,6 +466,8 @@ include::config/trace2.txt[]
 
 include::config/transfer.txt[]
 
+include::config/update.txt[]
+
 include::config/uploadarchive.txt[]
 
 include::config/uploadpack.txt[]

@@ -0,0 +1,4 @@
+update.mode::
+	When `git update` is run, this determines the mode of operation,
+	possible values are 'fast-forward', 'merge', and 'rebase'. The default
+	is 'fast-forward'.

@@ -5,9 +5,11 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "run-command.h"
+#include "config.h"
 #include "dir.h"
 
 enum update_mode_type {
+	UPDATE_MODE_INVALID = -1,
 	UPDATE_MODE_FAST_FORWARD = 0,
 	UPDATE_MODE_MERGE,
 	UPDATE_MODE_REBASE

@@ -34,6 +36,28 @@ static struct option update_options[] = {
 	OPT_END()
 };
 
+static enum update_mode_type update_mode_parse_value(const char *value)
+{
+	if (!strcmp(value, "fast-forward"))
+		return UPDATE_MODE_FAST_FORWARD;
+	if (!strcmp(value, "merge"))
+		return UPDATE_MODE_MERGE;
+	if (!strcmp(value, "rebase"))
+		return UPDATE_MODE_REBASE;
+
+	return UPDATE_MODE_INVALID;
+}
+
+static int git_update_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "update.mode")) {
+		mode = update_mode_parse_value(value);
+		return 0;
+	}
+
+	return git_default_config(var, value, cb);
+}
+
 static int run_fetch(void)
 {
 	struct strvec args = STRVEC_INIT;

@@ -87,6 +111,8 @@ int cmd_update(int argc, const char **argv, const char *prefix)
 	if (!getenv("GIT_REFLOG_ACTION"))
 		setenv("GIT_REFLOG_ACTION", "update", 0);
 
+	git_config(git_update_config, NULL);
+
 	argc = parse_options(argc, argv, prefix, update_options, update_usage, 0);
 
 	if (repo_read_index_unmerged(the_repository))

@@ -96,6 +96,11 @@ mode.
 it unless you understand the implications (see linkgit:git-rebase[1]
 for details).
 
+branch.<name>.updateMode::
+	When `git update` is run, this determines the mode of operation,
+	possible values are 'fast-forward', 'merge', and 'rebase'.
+	See `update.mode` for doing this in a non branch-specific manner.
+
 branch.<name>.description::
 	Branch description, can be edited with
 	`git branch --edit-description`. Branch description is

@@ -1,4 +1,5 @@
 update.mode::
 	When `git update` is run, this determines the mode of operation,
 	possible values are 'fast-forward', 'merge', and 'rebase'. The default
-	is 'fast-forward'.
+	is 'fast-forward'. See "branch.<name>.updateMode" for setting this on a
+	per-branch basis.

@@ -7,6 +7,7 @@
 #include "run-command.h"
 #include "config.h"
 #include "dir.h"
+#include "remote.h"
 
 enum update_mode_type {
 	UPDATE_MODE_INVALID = -1,

@@ -58,6 +59,22 @@ static int git_update_config(const char *var, const char *value, void *cb)
 	return git_default_config(var, value, cb);
 }
 
+static void get_branch_config(void)
+{
+	struct branch *cur_branch = branch_get("HEAD");
+	char *key;
+	const char *value;
+
+	if (!cur_branch)
+		return;
+
+	key = xstrfmt("branch.%s.updatemode", cur_branch->name);
+	if (!git_config_get_value(key, &value))
+		mode = update_mode_parse_value(value);
+
+	free(key);
+}
+
 static int run_fetch(void)
 {
 	struct strvec args = STRVEC_INIT;

@@ -112,6 +129,7 @@ int cmd_update(int argc, const char **argv, const char *prefix)
 		setenv("GIT_REFLOG_ACTION", "update", 0);
 
 	git_config(git_update_config, NULL);
+	get_branch_config();
 
 	argc = parse_options(argc, argv, prefix, update_options, update_usage, 0);
 

@@ -947,7 +947,6 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 	struct oid_array merge_heads = OID_ARRAY_INIT;
 	struct object_id orig_head, curr_head;
 	struct object_id rebase_fork_point;
-	int autostash;
 	int rebase_unspecified = 0;
 	int can_ff;
 

@@ -982,8 +981,8 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 	if (get_oid("HEAD", &orig_head))
 		oidclr(&orig_head);
 
-	autostash = config_autostash;
 	if (opt_rebase) {
+		int autostash = config_autostash;
 		if (opt_autostash != -1)
 			autostash = opt_autostash;
 

@@ -1065,13 +1064,12 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 		     recurse_submodules == RECURSE_SUBMODULES_ON_DEMAND) &&
 		    submodule_touches_in_range(the_repository, &upstream, &curr_head))
 			die(_("cannot rebase with locally recorded submodule modifications"));
-		if (!autostash) {
-			if (can_ff) {
-				/* we can fast-forward this without invoking rebase */
-				opt_ff = "--ff-only";
-				ran_ff = 1;
-				ret = run_merge();
-			}
+
+		if (can_ff) {
+			/* we can fast-forward this without invoking rebase */
+			opt_ff = "--ff-only";
+			ran_ff = 1;
+			ret = run_merge();
 		}
 		if (!ran_ff)
 			ret = run_rebase(&newbase, &upstream);

@@ -1053,7 +1053,6 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 
 	if (opt_rebase) {
 		int ret = 0;
-		int ran_ff = 0;
 
 		struct object_id newbase;
 		struct object_id upstream;

@@ -1068,11 +1067,10 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 		if (can_ff) {
 			/* we can fast-forward this without invoking rebase */
 			opt_ff = "--ff-only";
-			ran_ff = 1;
 			ret = run_merge();
-		}
-		if (!ran_ff)
+		} else {
 			ret = run_rebase(&newbase, &upstream);
+		}
 
 		if (!ret && (recurse_submodules == RECURSE_SUBMODULES_ON ||
 			     recurse_submodules == RECURSE_SUBMODULES_ON_DEMAND))

@@ -126,9 +126,9 @@ static struct option pull_options[] = {
 	/* Options passed to git-merge or git-rebase */
 	OPT_GROUP(N_("Options related to merging")),
 	OPT_CALLBACK_F('r', "rebase", &opt_rebase,
-	  "(false|true|merges|preserve|interactive)",
-	  N_("incorporate changes by rebasing rather than merging"),
-	  PARSE_OPT_OPTARG, parse_opt_rebase),
+		"(false|true|merges|preserve|interactive)",
+		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),