patch, 3 partsrebase: learn --keep-base

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..fffee89064 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1018,6 +1018,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1051,6 +1052,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1217,6 +1220,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1541,10 +1551,19 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+	    strbuf_reset(&buf);
+	    strbuf_addstr(&buf, options.upstream_name);
+	    strbuf_addstr(&buf, "...");
+	    options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
 		if (get_oid_mb(options.onto_name, &merge_base) < 0)
+		    if (keep_base)
+			die(_("'%s': need exactly one merge base with branch"),
+				options.upstream_name);
+		    else
 			die(_("'%s': need exactly one merge base"),
 			    options.onto_name);
 		options.onto = lookup_commit_or_die(&merge_base,

diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..780d381667 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,12 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -863,7 +869,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 

Documentation/git-rebase.txt, builtin/rebase.c, t/t3416-rebase-onto-threedots.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..27be1f48ff 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,19 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -364,6 +377,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -539,6 +556,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -863,7 +882,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..7c14a00460 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1018,6 +1018,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1051,6 +1052,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1217,6 +1220,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1541,12 +1551,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..8e2483b73e
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E       (master)
+#     \
+#      C*---F---G (side)
+#
+# C was formerly part of master but is side out
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase() {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $@" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $@ &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A' ''
+test_rebase 'G F D B A' '--onto D'
+test_rebase 'G F C E D B A' '--no-fork-point'
+test_rebase 'G F C D B A' '--no-fork-point --onto D'
+test_rebase 'G F E D B A' '--fork-point refs/heads/master'
+test_rebase 'G F D B A' '--fork-point --onto D refs/heads/master'
+test_rebase 'G F C E D B A' 'refs/heads/master'
+test_rebase 'G F C D B A' '--onto D refs/heads/master'
+
+test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 4607e65de6..b41a0c0b68 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -34,7 +34,7 @@ test_rebase() {
 		git reset --hard E &&
 		git checkout side &&
 		git reset --hard G &&
-		git rebase $@ &&
+		eval git rebase \"$@\" &&
 		test_write_lines $expected >expect &&
 		git log --pretty=%s >actual &&
 		test_cmp expect actual
-- snap --

Ciao,
Dscho

> +		test_write_lines $expected >expect &&
> +		git log --pretty=%s >actual &&
> +		test_cmp expect actual
> +	"
> +}
> +
> +test_rebase 'G F E D B A' ''
> +test_rebase 'G F D B A' '--onto D'
> +test_rebase 'G F C E D B A' '--no-fork-point'
> +test_rebase 'G F C D B A' '--no-fork-point --onto D'
> +test_rebase 'G F E D B A' '--fork-point refs/heads/master'
> +test_rebase 'G F D B A' '--fork-point --onto D refs/heads/master'
> +test_rebase 'G F C E D B A' 'refs/heads/master'
> +test_rebase 'G F C D B A' '--onto D refs/heads/master'
> +
> +test_done
> --
> 2.21.0.695.gaf8658f249
>
>

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 4607e65de6..daa0c77467 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -29,29 +29,29 @@ test_expect_success setup '
 test_rebase() {
 	expected="$1" &&
 	shift &&
-	test_expect_success "git rebase $@" "
+	test_expect_success "git rebase $*" "
 		git checkout master &&
 		git reset --hard E &&
 		git checkout side &&
 		git reset --hard G &&
-		git rebase $@ &&
+		eval git rebase $* &&
 		test_write_lines $expected >expect &&
 		git log --pretty=%s >actual &&
 		test_cmp expect actual
 	"
 }

-test_rebase 'G F E D B A' ''
-test_rebase 'G F D B A' '--onto D'
-test_rebase 'G F B A' '--keep-base'
-test_rebase 'G F C E D B A' '--no-fork-point'
-test_rebase 'G F C D B A' '--no-fork-point --onto D'
-test_rebase 'G F C B A' '--no-fork-point --keep-base'
-test_rebase 'G F E D B A' '--fork-point refs/heads/master'
-test_rebase 'G F D B A' '--fork-point --onto D refs/heads/master'
-test_rebase 'G F B A' '--fork-point --keep-base refs/heads/master'
-test_rebase 'G F C E D B A' 'refs/heads/master'
-test_rebase 'G F C D B A' '--onto D refs/heads/master'
-test_rebase 'G F C B A' '--keep-base refs/heads/master'
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master

 test_done
--
2.21.0.windows.1.152.g5895f170b6

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..3e6362dd9c
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,59 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head() {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $@ with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $@ &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success ''
+test_rebase_same_head success 'master'
+test_rebase_same_head success '--onto B B'
+test_rebase_same_head success '--onto B... B'
+test_rebase_same_head success '--onto master... master'
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success ''
+test_rebase_same_head success 'master'
+test_rebase_same_head success '--onto B B'
+test_rebase_same_head success '--onto B... B'
+test_rebase_same_head success '--onto master... master'
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success '--onto B B'
+test_rebase_same_head success '--onto B... B'
+test_rebase_same_head failure '--onto master... master'
+
+test_done

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..7aa6a090d4 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -895,12 +895,12 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
 		return 0;
@@ -908,12 +908,29 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	merge_bases = get_merge_bases(onto, head);
 	if (merge_bases && !merge_bases->next) {
 		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
+		if (!oideq(merge_base, &onto->object.oid))
+			goto done;
 	} else {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
+
+	if (!upstream)
+		goto done;
+
 	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (merge_bases && !merge_bases->next) {
+		if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+			goto done;
+	} else
+		goto done;
+
+	res = 1;
+
+done:
+	if (merge_bases)
+		free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 
@@ -1682,13 +1699,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * but this should be done if this is not an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head, &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
@@ -1782,7 +1796,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
 	if (reset_head(&options.onto->object.oid, "checkout", NULL,
-		       RESET_HEAD_DETACH | RESET_ORIG_HEAD | 
+		       RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 		       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
 		       NULL, msg.buf))
 		die(_("Could not detach HEAD"));
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 460d0523be..604d624ff8 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase--am.sh and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b60b11f9f2..f054186cc7 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1066,7 +1066,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 3e6362dd9c..414b4216d6 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -54,6 +54,6 @@ test_expect_success 'add work to upstream' '
 changes='our and their changes'
 test_rebase_same_head success '--onto B B'
 test_rebase_same_head success '--onto B... B'
-test_rebase_same_head failure '--onto master... master'
+test_rebase_same_head success '--onto master... master'
 
 test_done

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..fe61c2a899 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1682,13 +1682,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * but this should be done if this is not an interactive rebase.
 	 */
 	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 460d0523be..604d624ff8 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase--am.sh and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b60b11f9f2..f054186cc7 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1066,7 +1066,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 3e6362dd9c..414b4216d6 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -54,6 +54,6 @@ test_expect_success 'add work to upstream' '
 changes='our and their changes'
 test_rebase_same_head success '--onto B B'
 test_rebase_same_head success '--onto B... B'
-test_rebase_same_head failure '--onto master... master'
+test_rebase_same_head success '--onto master... master'
 
 test_done

Documentation/git-rebase.txt, builtin/rebase.c, t/t3416-rebase-onto-threedots.sh, t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..569ab708d4 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,24 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+This option is useful in the case where one is developing a feature on
+top of an upstream branch. While the feature is being worked on, the
+upstream branch may advance and it may not be the best idea to keep
+rebasing on top of the upstream but to keep the base commit as-is.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -364,6 +382,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -539,6 +561,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -863,7 +887,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 7aa6a090d4..caec1b56e8 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1035,6 +1035,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1068,6 +1069,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1234,6 +1237,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1558,12 +1568,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 8e2483b73e..0311bcbc68 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase() {
 
 test_rebase 'G F E D B A' ''
 test_rebase 'G F D B A' '--onto D'
+test_rebase 'G F B A' '--keep-base'
 test_rebase 'G F C E D B A' '--no-fork-point'
 test_rebase 'G F C D B A' '--no-fork-point --onto D'
+test_rebase 'G F C B A' '--no-fork-point --keep-base'
 test_rebase 'G F E D B A' '--fork-point refs/heads/master'
 test_rebase 'G F D B A' '--fork-point --onto D refs/heads/master'
+test_rebase 'G F B A' '--fork-point --keep-base refs/heads/master'
 test_rebase 'G F C E D B A' 'refs/heads/master'
 test_rebase 'G F C D B A' '--onto D refs/heads/master'
+test_rebase 'G F C B A' '--keep-base refs/heads/master'
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 414b4216d6..8585c21c5c 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -33,6 +33,7 @@ test_rebase_same_head success 'master'
 test_rebase_same_head success '--onto B B'
 test_rebase_same_head success '--onto B... B'
 test_rebase_same_head success '--onto master... master'
+test_rebase_same_head success '--keep-base master'
 
 test_expect_success 'add work to side' '
 	test_commit E
@@ -44,6 +45,7 @@ test_rebase_same_head success 'master'
 test_rebase_same_head success '--onto B B'
 test_rebase_same_head success '--onto B... B'
 test_rebase_same_head success '--onto master... master'
+test_rebase_same_head success '--keep-base master'
 
 test_expect_success 'add work to upstream' '
 	git checkout master &&
@@ -55,5 +57,6 @@ changes='our and their changes'
 test_rebase_same_head success '--onto B B'
 test_rebase_same_head success '--onto B... B'
 test_rebase_same_head success '--onto master... master'
+test_rebase_same_head success '--keep-base master'
 
 test_done

t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 0311bcbc68..e63040932f 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -11,7 +11,7 @@ test_description='git rebase --fork-point test'
 #     \
 #      C*---F---G (side)
 #
-# C was formerly part of master but is side out
+# C was formerly part of master but master was rewound to remove C
 #
 test_expect_success setup '
 	test_commit A &&
@@ -29,29 +29,29 @@ test_expect_success setup '
 test_rebase() {
 	expected="$1" &&
 	shift &&
-	test_expect_success "git rebase $@" "
+	test_expect_success "git rebase $*" "
 		git checkout master &&
 		git reset --hard E &&
 		git checkout side &&
 		git reset --hard G &&
-		git rebase $@ &&
+		git rebase $* &&
 		test_write_lines $expected >expect &&
 		git log --pretty=%s >actual &&
 		test_cmp expect actual
 	"
 }
 
-test_rebase 'G F E D B A' ''
-test_rebase 'G F D B A' '--onto D'
-test_rebase 'G F B A' '--keep-base'
-test_rebase 'G F C E D B A' '--no-fork-point'
-test_rebase 'G F C D B A' '--no-fork-point --onto D'
-test_rebase 'G F C B A' '--no-fork-point --keep-base'
-test_rebase 'G F E D B A' '--fork-point refs/heads/master'
-test_rebase 'G F D B A' '--fork-point --onto D refs/heads/master'
-test_rebase 'G F B A' '--fork-point --keep-base refs/heads/master'
-test_rebase 'G F C E D B A' 'refs/heads/master'
-test_rebase 'G F C D B A' '--onto D refs/heads/master'
-test_rebase 'G F C B A' '--keep-base refs/heads/master'
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 8585c21c5c..f493ce64c4 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -18,34 +18,34 @@ test_expect_success setup '
 test_rebase_same_head() {
 	status="$1" &&
 	shift &&
-	test_expect_$status "git rebase $@ with $changes is no-op" "
+	test_expect_$status "git rebase $* with $changes is no-op" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
-		git rebase $@ &&
+		git rebase $* &&
 		newhead=\$(git rev-parse HEAD) &&
 		test_cmp_rev \$oldhead \$newhead
 	"
 }
 
 changes='no changes'
-test_rebase_same_head success ''
-test_rebase_same_head success 'master'
-test_rebase_same_head success '--onto B B'
-test_rebase_same_head success '--onto B... B'
-test_rebase_same_head success '--onto master... master'
-test_rebase_same_head success '--keep-base master'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
 
 test_expect_success 'add work to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success ''
-test_rebase_same_head success 'master'
-test_rebase_same_head success '--onto B B'
-test_rebase_same_head success '--onto B... B'
-test_rebase_same_head success '--onto master... master'
-test_rebase_same_head success '--keep-base master'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
 
 test_expect_success 'add work to upstream' '
 	git checkout master &&
@@ -54,9 +54,9 @@ test_expect_success 'add work to upstream' '
 '
 
 changes='our and their changes'
-test_rebase_same_head success '--onto B B'
-test_rebase_same_head success '--onto B... B'
-test_rebase_same_head success '--onto master... master'
-test_rebase_same_head success '--keep-base master'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
 
 test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..6d523123d0
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E       (master)
+#     \
+#      C*---F---G (side)
+#
+# C was formerly part of master but master was rewound to remove C
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase() {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $*" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $* &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..b7c9af17c3
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,59 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head() {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $* &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+
+test_done

Documentation/git-rebase.txt, builtin/rebase.c, t/t3416-rebase-onto-threedots.sh, t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..569ab708d4 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,24 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+This option is useful in the case where one is developing a feature on
+top of an upstream branch. While the feature is being worked on, the
+upstream branch may advance and it may not be the best idea to keep
+rebasing on top of the upstream but to keep the base commit as-is.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -364,6 +382,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -539,6 +561,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -863,7 +887,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 7aa6a090d4..caec1b56e8 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1035,6 +1035,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1068,6 +1069,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1234,6 +1237,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1558,12 +1568,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 6d523123d0..e63040932f 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase() {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
 test_rebase 'G F E D B A' --fork-point refs/heads/master
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
 test_rebase 'G F C E D B A' refs/heads/master
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 357cf17bdd..f493ce64c4 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -33,6 +33,7 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
 
 test_expect_success 'add work to side' '
 	test_commit E
@@ -44,6 +45,7 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
 
 test_expect_success 'add work to upstream' '
 	git checkout master &&
@@ -55,5 +57,6 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
 
 test_done

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..7aa6a090d4 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -895,12 +895,12 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
 		return 0;
@@ -908,12 +908,29 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	merge_bases = get_merge_bases(onto, head);
 	if (merge_bases && !merge_bases->next) {
 		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
+		if (!oideq(merge_base, &onto->object.oid))
+			goto done;
 	} else {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
+
+	if (!upstream)
+		goto done;
+
 	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (merge_bases && !merge_bases->next) {
+		if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+			goto done;
+	} else
+		goto done;
+
+	res = 1;
+
+done:
+	if (merge_bases)
+		free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 
@@ -1682,13 +1699,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * but this should be done if this is not an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head, &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
@@ -1782,7 +1796,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
 	if (reset_head(&options.onto->object.oid, "checkout", NULL,
-		       RESET_HEAD_DETACH | RESET_ORIG_HEAD | 
+		       RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 		       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
 		       NULL, msg.buf))
 		die(_("Could not detach HEAD"));
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 460d0523be..604d624ff8 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase--am.sh and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b60b11f9f2..f054186cc7 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1066,7 +1066,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index b7c9af17c3..357cf17bdd 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -54,6 +54,6 @@ test_expect_success 'add work to upstream' '
 changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
-test_rebase_same_head failure --onto master... master
+test_rebase_same_head success --onto master... master
 
 test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..6d523123d0
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E       (master)
+#     \
+#      C*---F---G (side)
+#
+# C was formerly part of master but master was rewound to remove C
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase() {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $*" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $* &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..4f04d67fd7
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head() {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $* &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head failure --fork-point --onto master... master
+
+test_done

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..7aa6a090d4 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -895,12 +895,12 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
 		return 0;
@@ -908,12 +908,29 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	merge_bases = get_merge_bases(onto, head);
 	if (merge_bases && !merge_bases->next) {
 		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
+		if (!oideq(merge_base, &onto->object.oid))
+			goto done;
 	} else {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
+
+	if (!upstream)
+		goto done;
+
 	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (merge_bases && !merge_bases->next) {
+		if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+			goto done;
+	} else
+		goto done;
+
+	res = 1;
+
+done:
+	if (merge_bases)
+		free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 
@@ -1682,13 +1699,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * but this should be done if this is not an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head, &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
@@ -1782,7 +1796,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
 	if (reset_head(&options.onto->object.oid, "checkout", NULL,
-		       RESET_HEAD_DETACH | RESET_ORIG_HEAD | 
+		       RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 		       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
 		       NULL, msg.buf))
 		die(_("Could not detach HEAD"));
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 460d0523be..604d624ff8 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase--am.sh and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b60b11f9f2..f054186cc7 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1066,7 +1066,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 4f04d67fd7..d0e5b1f3e6 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -64,9 +64,9 @@ test_expect_success 'add work to upstream' '
 changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
-test_rebase_same_head failure --onto master... master
+test_rebase_same_head success --onto master... master
 test_rebase_same_head failure --fork-point --onto B B
 test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head failure --fork-point --onto master... master
+test_rebase_same_head success --fork-point --onto master... master
 
 test_done

builtin/rebase.c, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 7aa6a090d4..5f00d91b68 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -896,6 +896,7 @@ static int is_linear_history(struct commit *from, struct commit *to)
 }
 
 static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct commit *restrict_revision,
 			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
@@ -915,6 +916,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
 		goto done;
 	}
 
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+		goto done;
+
 	if (!upstream)
 		goto done;
 
@@ -1701,8 +1705,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * Check if we are already based on onto with linear history,
 	 * but this should be done if this is not an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, options.upstream, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision) {
+	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+		    &options.orig_head, &merge_base) &&
+	    !is_interactive(&options)) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d0e5b1f3e6..1cb2896fb4 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -35,8 +35,8 @@ test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
 test_rebase_same_head success --no-fork-point
 test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_expect_success 'add work to side' '
@@ -51,8 +51,8 @@ test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
 test_rebase_same_head success --no-fork-point
 test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_expect_success 'add work to upstream' '
@@ -65,8 +65,8 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_done

Documentation/git-rebase.txt, builtin/rebase.c, t/t3416-rebase-onto-threedots.sh, t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..569ab708d4 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,24 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+This option is useful in the case where one is developing a feature on
+top of an upstream branch. While the feature is being worked on, the
+upstream branch may advance and it may not be the best idea to keep
+rebasing on top of the upstream but to keep the base commit as-is.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -364,6 +382,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -539,6 +561,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -863,7 +887,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 5f00d91b68..289763651e 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1039,6 +1039,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1072,6 +1073,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1238,6 +1241,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1562,12 +1572,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 6d523123d0..e63040932f 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase() {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
 test_rebase 'G F E D B A' --fork-point refs/heads/master
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
 test_rebase 'G F C E D B A' refs/heads/master
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 1cb2896fb4..1ba02cc95f 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -33,11 +33,15 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --keep-base --no-fork-point
 test_rebase_same_head success --fork-point master
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_expect_success 'add work to side' '
 	test_commit E
@@ -49,11 +53,15 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --keep-base --no-fork-point
 test_rebase_same_head success --fork-point master
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_expect_success 'add work to upstream' '
 	git checkout master &&
@@ -65,8 +73,11 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..9b517d87a3
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E    (master)
+#      \
+#       C*---F---G (side)
+#
+# C was formerly part of master but master was rewound to remove C
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase() {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $*" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $* &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..4f04d67fd7
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head() {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $* &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head failure --fork-point --onto master... master
+
+test_done

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..de10b6f5ad 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -899,21 +899,27 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 			    struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
-		return 0;
+		goto done;
 
 	merge_bases = get_merge_bases(onto, head);
-	if (merge_bases && !merge_bases->next) {
-		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
-	} else {
+	if (!merge_bases || merge_bases->next) {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
-	free_commit_list(merge_bases);
+
+	oidcpy(merge_base, &merge_bases->item->object.oid);
+	if (!oideq(merge_base, &onto->object.oid))
+		goto done;
+
+	res = 1;
+
+done:
+	if (merge_bases)
+		free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index de10b6f5ad..f5aca1eee0 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -895,8 +895,8 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
 	struct commit_list *merge_bases = NULL;
@@ -915,6 +915,18 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (!upstream)
+		goto done;
+
+	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (!merge_bases || merge_bases->next) {
+		goto done;
+	}
+
+	if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+		goto done;
+
 	res = 1;
 
 done:
@@ -1688,13 +1700,11 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * but this should be done if this is not an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
+		    &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
@@ -1788,7 +1798,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
 	if (reset_head(&options.onto->object.oid, "checkout", NULL,
-		       RESET_HEAD_DETACH | RESET_ORIG_HEAD | 
+		       RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 		       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
 		       NULL, msg.buf))
 		die(_("Could not detach HEAD"));
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 460d0523be..604d624ff8 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase--am.sh and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b60b11f9f2..f054186cc7 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1066,7 +1066,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 4f04d67fd7..d0e5b1f3e6 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -64,9 +64,9 @@ test_expect_success 'add work to upstream' '
 changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
-test_rebase_same_head failure --onto master... master
+test_rebase_same_head success --onto master... master
 test_rebase_same_head failure --fork-point --onto B B
 test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head failure --fork-point --onto master... master
+test_rebase_same_head success --fork-point --onto master... master
 
 test_done

builtin/rebase.c, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index f5aca1eee0..2e29ea652f 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -896,6 +896,7 @@ static int is_linear_history(struct commit *from, struct commit *to)
 }
 
 static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct commit *restrict_revision,
 			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
@@ -915,6 +916,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+		goto done;
+
 	if (!upstream)
 		goto done;
 
@@ -1702,9 +1706,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * Check if we are already based on onto with linear history,
 	 * but this should be done if this is not an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
-		    &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision) {
+	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+		    &options.orig_head, &merge_base) &&
+	    !is_interactive(&options)) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d0e5b1f3e6..1cb2896fb4 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -35,8 +35,8 @@ test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
 test_rebase_same_head success --no-fork-point
 test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_expect_success 'add work to side' '
@@ -51,8 +51,8 @@ test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
 test_rebase_same_head success --no-fork-point
 test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_expect_success 'add work to upstream' '
@@ -65,8 +65,8 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_done

Documentation/git-rebase.txt, builtin/rebase.c, t/t3416-rebase-onto-threedots.sh, t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..569ab708d4 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,24 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+This option is useful in the case where one is developing a feature on
+top of an upstream branch. While the feature is being worked on, the
+upstream branch may advance and it may not be the best idea to keep
+rebasing on top of the upstream but to keep the base commit as-is.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -364,6 +382,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -539,6 +561,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -863,7 +887,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 2e29ea652f..87a23f17eb 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1040,6 +1040,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1073,6 +1074,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1239,6 +1242,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1563,12 +1573,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 9b517d87a3..f848946f5a 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase() {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
 test_rebase 'G F E D B A' --fork-point refs/heads/master
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
 test_rebase 'G F C E D B A' refs/heads/master
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 1cb2896fb4..1ba02cc95f 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -33,11 +33,15 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --keep-base --no-fork-point
 test_rebase_same_head success --fork-point master
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_expect_success 'add work to side' '
 	test_commit E
@@ -49,11 +53,15 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --keep-base --no-fork-point
 test_rebase_same_head success --fork-point master
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_expect_success 'add work to upstream' '
 	git checkout master &&
@@ -65,8 +73,11 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_done

builtin/rebase.c, contrib/completion/git-completion.bash

diff --git a/builtin/rebase.c b/builtin/rebase.c
index cf63195e7d..19e7e2a1c9 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1723,7 +1723,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done if this is not an interactive rebase.
+	 * in which case we could fast-forward without replacing the commits
+	 * with new commits recreated by replaying their changes. This
+	 * optimization must not be done if this is an interactive rebase.
 	 */
 	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
 		    &options.orig_head, &merge_base) &&
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 976e4a6548..f9dc431a39 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -2027,7 +2027,7 @@ _git_rebase ()
 			--autosquash --no-autosquash
 			--fork-point --no-fork-point
 			--autostash --no-autostash
-			--verify --no-verify
+			--verify --no-verify --keep-base
 			--keep-empty --root --force-rebase --no-ff
 			--rerere-autoupdate
 			--exec

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..9b517d87a3
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E    (master)
+#      \
+#       C*---F---G (side)
+#
+# C was formerly part of master but master was rewound to remove C
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase() {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $*" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $* &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..4f04d67fd7
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head() {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $* &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head failure --fork-point --onto master... master
+
+test_done

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 77deebc65c..de10b6f5ad 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -899,21 +899,27 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 			    struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
-		return 0;
+		goto done;
 
 	merge_bases = get_merge_bases(onto, head);
-	if (merge_bases && !merge_bases->next) {
-		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
-	} else {
+	if (!merge_bases || merge_bases->next) {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
-	free_commit_list(merge_bases);
+
+	oidcpy(merge_base, &merge_bases->item->object.oid);
+	if (!oideq(merge_base, &onto->object.oid))
+		goto done;
+
+	res = 1;
+
+done:
+	if (merge_bases)
+		free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index de10b6f5ad..fdb42eb09f 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -895,8 +895,8 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
 	struct commit_list *merge_bases = NULL;
@@ -915,6 +915,17 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (!upstream)
+		goto done;
+
+	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (!merge_bases || merge_bases->next)
+		goto done;
+
+	if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+		goto done;
+
 	res = 1;
 
 done:
@@ -1688,13 +1699,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * in which case we could fast-forward without replacing the commits
+	 * with new commits recreated by replaying their changes. This
+	 * optimization must not be done if this is an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
+		    &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
@@ -1788,7 +1799,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
 	if (reset_head(&options.onto->object.oid, "checkout", NULL,
-		       RESET_HEAD_DETACH | RESET_ORIG_HEAD | 
+		       RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 		       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
 		       NULL, msg.buf))
 		die(_("Could not detach HEAD"));
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 460d0523be..604d624ff8 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase--am.sh and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b60b11f9f2..f054186cc7 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1066,7 +1066,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 4f04d67fd7..d0e5b1f3e6 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -64,9 +64,9 @@ test_expect_success 'add work to upstream' '
 changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
-test_rebase_same_head failure --onto master... master
+test_rebase_same_head success --onto master... master
 test_rebase_same_head failure --fork-point --onto B B
 test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head failure --fork-point --onto master... master
+test_rebase_same_head success --fork-point --onto master... master
 
 test_done

builtin/rebase.c, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index fdb42eb09f..66c59ebe22 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -896,6 +896,7 @@ static int is_linear_history(struct commit *from, struct commit *to)
 }
 
 static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct commit *restrict_revision,
 			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
@@ -915,6 +916,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+		goto done;
+
 	if (!upstream)
 		goto done;
 
@@ -1703,9 +1707,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * with new commits recreated by replaying their changes. This
 	 * optimization must not be done if this is an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
-		    &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision) {
+	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+		    &options.orig_head, &merge_base) &&
+	    !is_interactive(&options)) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d0e5b1f3e6..1cb2896fb4 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -35,8 +35,8 @@ test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
 test_rebase_same_head success --no-fork-point
 test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_expect_success 'add work to side' '
@@ -51,8 +51,8 @@ test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
 test_rebase_same_head success --no-fork-point
 test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_expect_success 'add work to upstream' '
@@ -65,8 +65,8 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto B B
+test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
 
 test_done

Documentation/git-rebase.txt, builtin/rebase.c, contrib/completion/git-completion.bash, t/t3416-rebase-onto-threedots.sh, t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6363d674b7..569ab708d4 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' --continue | --skip | --abort | --quit | --edit-todo | --show-current-patch
@@ -217,6 +217,24 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+This option is useful in the case where one is developing a feature on
+top of an upstream branch. While the feature is being worked on, the
+upstream branch may advance and it may not be the best idea to keep
+rebasing on top of the upstream but to keep the base commit as-is.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -364,6 +382,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -539,6 +561,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -863,7 +887,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 66c59ebe22..19e7e2a1c9 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,8 +27,8 @@
 #include "branch.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1039,6 +1039,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	};
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1072,6 +1073,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1238,6 +1241,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != NO_ACTION && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1562,12 +1572,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 976e4a6548..f9dc431a39 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -2027,7 +2027,7 @@ _git_rebase ()
 			--autosquash --no-autosquash
 			--fork-point --no-fork-point
 			--autostash --no-autostash
-			--verify --no-verify
+			--verify --no-verify --keep-base
 			--keep-empty --root --force-rebase --no-ff
 			--rerere-autoupdate
 			--exec
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 9b517d87a3..f848946f5a 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase() {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
 test_rebase 'G F E D B A' --fork-point refs/heads/master
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
 test_rebase 'G F C E D B A' refs/heads/master
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 1cb2896fb4..1ba02cc95f 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -33,11 +33,15 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --keep-base --no-fork-point
 test_rebase_same_head success --fork-point master
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_expect_success 'add work to side' '
 	test_commit E
@@ -49,11 +53,15 @@ test_rebase_same_head success master
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --keep-base --no-fork-point
 test_rebase_same_head success --fork-point master
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_expect_success 'add work to upstream' '
 	git checkout master &&
@@ -65,8 +73,11 @@ changes='our and their changes'
 test_rebase_same_head success --onto B B
 test_rebase_same_head success --onto B... B
 test_rebase_same_head success --onto master... master
+test_rebase_same_head success --keep-base master
+test_rebase_same_head success --keep-base
 test_rebase_same_head success --fork-point --onto B B
 test_rebase_same_head success --fork-point --onto B... B
 test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success --fork-point --keep-base master
 
 test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..2d5c6e641e
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E    (master)
+#      \
+#       C*---F---G (side)
+#
+# C was formerly part of master but master was rewound to remove C
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase () {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $*" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $* &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index f49af274e0..d9f20fa07c 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -18,55 +18,72 @@ test_expect_success setup '
 test_rebase_same_head () {
 	status="$1" &&
 	shift &&
-	test_expect_$status "git rebase $* with $changes is no-op" "
+	what="$1" &&
+	shift &&
+	cmp="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is $what" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
-		git rebase $* &&
+		git rebase $* >stdout &&
+		if test $what = work
+		then
+			test_i18ngrep 'rewinding head' stdout
+		elif test $what = noop
+		then
+			test_i18ngrep 'is up to date' stdout
+		fi &&
 		newhead=\$(git rev-parse HEAD) &&
-		test_cmp_rev \$oldhead \$newhead
+		if test $cmp = same
+		then
+			test_cmp_rev \$oldhead \$newhead
+		elif test $cmp = diff
+		then
+			! test_cmp_rev \$oldhead \$newhead
+		fi
 	"
 }
 
 changes='no changes'
-test_rebase_same_head success
-test_rebase_same_head success master
-test_rebase_same_head success --onto B B
-test_rebase_same_head success --onto B... B
-test_rebase_same_head success --onto master... master
-test_rebase_same_head success --no-fork-point
-test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success work same
+test_rebase_same_head success noop same master
+test_rebase_same_head success noop same --onto B B
+test_rebase_same_head success noop same --onto B... B
+test_rebase_same_head success noop same --onto master... master
+test_rebase_same_head success noop same --no-fork-point
+test_rebase_same_head success work same --fork-point master
+test_rebase_same_head failure noop same --fork-point --onto B B
+test_rebase_same_head failure work same --fork-point --onto B... B
+test_rebase_same_head success work same --fork-point --onto master... master
 
-test_expect_success 'add work to side' '
+test_expect_success 'add work same to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success
-test_rebase_same_head success master
-test_rebase_same_head success --onto B B
-test_rebase_same_head success --onto B... B
-test_rebase_same_head success --onto master... master
-test_rebase_same_head success --no-fork-point
-test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success work same
+test_rebase_same_head success noop same master
+test_rebase_same_head success noop same --onto B B
+test_rebase_same_head success noop same --onto B... B
+test_rebase_same_head success noop same --onto master... master
+test_rebase_same_head success noop same --no-fork-point
+test_rebase_same_head success work same --fork-point master
+test_rebase_same_head failure work same --fork-point --onto B B
+test_rebase_same_head failure work same --fork-point --onto B... B
+test_rebase_same_head success work same --fork-point --onto master... master
 
-test_expect_success 'add work to upstream' '
+test_expect_success 'add work same to upstream' '
 	git checkout master &&
 	test_commit F &&
 	git checkout side
 '
 
 changes='our and their changes'
-test_rebase_same_head success --onto B B
-test_rebase_same_head success --onto B... B
-test_rebase_same_head failure --onto master... master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head failure --fork-point --onto master... master
+test_rebase_same_head success noop same --onto B B
+test_rebase_same_head success noop same --onto B... B
+test_rebase_same_head failure work same --onto master... master
+test_rebase_same_head failure work same --fork-point --onto B B
+test_rebase_same_head failure work same --fork-point --onto B... B
+test_rebase_same_head failure work same --fork-point --onto master... master
 
 test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..f49af274e0
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head () {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $* &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head failure --fork-point --onto master... master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d9f20fa07c..02b2516595 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -16,22 +16,47 @@ test_expect_success setup '
 '
 
 test_rebase_same_head () {
+	status_n="$1" &&
+	shift &&
+	what_n="$1" &&
+	shift &&
+	cmp_n="$1" &&
+	shift &&
+	status_f="$1" &&
+	shift &&
+	what_f="$1" &&
+	shift &&
+	cmp_f="$1" &&
+	shift &&
+	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+}
+
+test_rebase_same_head_ () {
 	status="$1" &&
 	shift &&
 	what="$1" &&
 	shift &&
 	cmp="$1" &&
 	shift &&
-	test_expect_$status "git rebase $* with $changes is $what" "
+	flag="$1"
+	shift &&
+	test_expect_$status "git rebase$flag $* with $changes is $what with $cmp HEAD" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
-		git rebase $* >stdout &&
+		git rebase$flag $* >stdout &&
 		if test $what = work
 		then
+			# Must check this case first, for 'is up to
+			# date, rebase forced[...]rewinding head' cases
 			test_i18ngrep 'rewinding head' stdout
 		elif test $what = noop
 		then
-			test_i18ngrep 'is up to date' stdout
+			test_i18ngrep 'is up to date' stdout &&
+			! test_i18ngrep 'rebase forced' stdout
+		elif test $what = noop-force
+		then
+			test_i18ngrep 'is up to date, rebase forced' stdout
 		fi &&
 		newhead=\$(git rev-parse HEAD) &&
 		if test $cmp = same
@@ -45,32 +70,32 @@ test_rebase_same_head () {
 }
 
 changes='no changes'
-test_rebase_same_head success work same
-test_rebase_same_head success noop same master
-test_rebase_same_head success noop same --onto B B
-test_rebase_same_head success noop same --onto B... B
-test_rebase_same_head success noop same --onto master... master
-test_rebase_same_head success noop same --no-fork-point
-test_rebase_same_head success work same --fork-point master
-test_rebase_same_head failure noop same --fork-point --onto B B
-test_rebase_same_head failure work same --fork-point --onto B... B
-test_rebase_same_head success work same --fork-point --onto master... master
+test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success noop-force same master
+test_rebase_same_head success noop same success noop-force diff --onto B B
+test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success work same success work same --fork-point master
+test_rebase_same_head failure noop same success work diff --fork-point --onto B B
+test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head success work same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success work same
-test_rebase_same_head success noop same master
-test_rebase_same_head success noop same --onto B B
-test_rebase_same_head success noop same --onto B... B
-test_rebase_same_head success noop same --onto master... master
-test_rebase_same_head success noop same --no-fork-point
-test_rebase_same_head success work same --fork-point master
-test_rebase_same_head failure work same --fork-point --onto B B
-test_rebase_same_head failure work same --fork-point --onto B... B
-test_rebase_same_head success work same --fork-point --onto master... master
+test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success noop-force same master
+test_rebase_same_head success noop same success noop-force diff --onto B B
+test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success work same success work same --fork-point master
+test_rebase_same_head failure work same success work diff --fork-point --onto B B
+test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head success work same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to upstream' '
 	git checkout master &&
@@ -79,11 +104,11 @@ test_expect_success 'add work same to upstream' '
 '
 
 changes='our and their changes'
-test_rebase_same_head success noop same --onto B B
-test_rebase_same_head success noop same --onto B... B
-test_rebase_same_head failure work same --onto master... master
-test_rebase_same_head failure work same --fork-point --onto B B
-test_rebase_same_head failure work same --fork-point --onto B... B
-test_rebase_same_head failure work same --fork-point --onto master... master
+test_rebase_same_head success noop same success noop-force diff --onto B B
+test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head failure work same success work diff --onto master... master
+test_rebase_same_head failure work same success work diff --fork-point --onto B B
+test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head failure work same success work diff --fork-point --onto master... master
 
 test_done

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 670096c065..22c4f1ff93 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1264,21 +1264,27 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 			    struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
-		return 0;
+		goto done;
 
 	merge_bases = get_merge_bases(onto, head);
-	if (merge_bases && !merge_bases->next) {
-		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
-	} else {
+	if (!merge_bases || merge_bases->next) {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
-	free_commit_list(merge_bases);
+
+	oidcpy(merge_base, &merge_bases->item->object.oid);
+	if (!oideq(merge_base, &onto->object.oid))
+		goto done;
+
+	res = 1;
+
+done:
+	if (merge_bases)
+		free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 22c4f1ff93..bdb1d922a4 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1260,8 +1260,8 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
 	struct commit_list *merge_bases = NULL;
@@ -1280,6 +1280,17 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (!upstream)
+		goto done;
+
+	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (!merge_bases || merge_bases->next)
+		goto done;
+
+	if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+		goto done;
+
 	res = 1;
 
 done:
@@ -2028,13 +2039,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * in which case we could fast-forward without replacing the commits
+	 * with new commits recreated by replaying their changes. This
+	 * optimization must not be done if this is an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
+		    &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 80b23fd326..d7c724bea3 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase --am and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 461dd539ff..3cc9052f10 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1058,7 +1058,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 02b2516595..d9957e5f1e 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -106,9 +106,9 @@ test_expect_success 'add work same to upstream' '
 changes='our and their changes'
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head failure work same success work diff --onto master... master
+test_rebase_same_head success noop same success work diff --onto master... master
 test_rebase_same_head failure work same success work diff --fork-point --onto B B
 test_rebase_same_head failure work same success work diff --fork-point --onto B... B
-test_rebase_same_head failure work same success work diff --fork-point --onto master... master
+test_rebase_same_head success noop same success work diff --fork-point --onto master... master
 
 test_done

builtin/rebase.c, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index bdb1d922a4..b78bd92002 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1261,6 +1261,7 @@ static int is_linear_history(struct commit *from, struct commit *to)
 }
 
 static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct commit *restrict_revision,
 			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
@@ -1280,6 +1281,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+		goto done;
+
 	if (!upstream)
 		goto done;
 
@@ -2043,9 +2047,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * with new commits recreated by replaying their changes. This
 	 * optimization must not be done if this is an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
-		    &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision) {
+	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+		    &options.orig_head, &merge_base) &&
+	    !is_interactive(&options)) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d9957e5f1e..fbedfe7b4a 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -70,32 +70,32 @@ test_rebase_same_head_ () {
 }
 
 changes='no changes'
-test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success work same
 test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
 test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success work same success work same --fork-point master
-test_rebase_same_head failure noop same success work diff --fork-point --onto B B
-test_rebase_same_head failure work same success work diff --fork-point --onto B... B
-test_rebase_same_head success work same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --fork-point master
+test_rebase_same_head success noop same success work diff --fork-point --onto B B
+test_rebase_same_head success noop same success work diff --fork-point --onto B... B
+test_rebase_same_head success noop same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success work same
 test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
 test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success work same success work same --fork-point master
-test_rebase_same_head failure work same success work diff --fork-point --onto B B
-test_rebase_same_head failure work same success work diff --fork-point --onto B... B
-test_rebase_same_head success work same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --fork-point master
+test_rebase_same_head success noop same success work diff --fork-point --onto B B
+test_rebase_same_head success noop same success work diff --fork-point --onto B... B
+test_rebase_same_head success noop same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to upstream' '
 	git checkout master &&

diff --git a/t/t3421-rebase-topology-linear.sh b/t/t3421-rebase-topology-linear.sh
index 7274dca40b..b847064f91 100755
--- a/t/t3421-rebase-topology-linear.sh
+++ b/t/t3421-rebase-topology-linear.sh
@@ -31,6 +31,16 @@ test_run_rebase success -m
 test_run_rebase success -i
 test_have_prereq !REBASE_P || test_run_rebase success -p
 
+test_expect_success 'setup branches and remote tracking' '
+	git tag -l >tags &&
+	for tag in $(cat tags)
+	do
+		git branch branch-$tag $tag || return 1
+	done &&
+	git remote add origin "file://$PWD" &&
+	git fetch origin
+'
+
 test_run_rebase () {
 	result=$1
 	shift
@@ -57,10 +67,28 @@ test_run_rebase () {
 	"
 }
 test_run_rebase success ''
+test_run_rebase success --fork-point
 test_run_rebase success -m
 test_run_rebase success -i
 test_have_prereq !REBASE_P || test_run_rebase failure -p
 
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* -f rewrites even if remote upstream is an ancestor" "
+		reset_rebase &&
+		git rebase $* -f branch-b branch-e &&
+		! test_cmp_rev branch-e origin/branch-e &&
+		test_cmp_rev branch-b HEAD~2 &&
+		test_linear_range 'd e' branch-b..
+	"
+}
+test_run_rebase success ''
+test_run_rebase success --fork-point
+test_run_rebase success -m
+test_run_rebase success -i
+test_have_prereq !REBASE_P || test_run_rebase success -p
+
 test_run_rebase () {
 	result=$1
 	shift
@@ -71,6 +99,7 @@ test_run_rebase () {
 	"
 }
 test_run_rebase success ''
+test_run_rebase success --fork-point
 test_run_rebase success -m
 test_run_rebase success -i
 test_have_prereq !REBASE_P || test_run_rebase success -p

Documentation/git-rebase.txt, builtin/rebase.c, contrib/completion/git-completion.bash, t/t3416-rebase-onto-threedots.sh, t/t3431-rebase-fork-point.sh, t/t3432-rebase-fast-forward.sh

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 6156609cf7..3146c1592d 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -8,8 +8,8 @@ git-rebase - Reapply commits on top of another base tip
 SYNOPSIS
 --------
 [verse]
-'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
-	[<upstream> [<branch>]]
+'git rebase' [-i | --interactive] [<options>] [--exec <cmd>]
+	[--onto <newbase> | --keep-base] [<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [<options>] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
 'git rebase' (--continue | --skip | --abort | --quit | --edit-todo | --show-current-patch)
@@ -217,6 +217,24 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+--keep-base::
+	Set the starting point at which to create the new commits to the
+	merge base of <upstream> <branch>. Running
+	'git rebase --keep-base <upstream> <branch>' is equivalent to
+	running 'git rebase --onto <upstream>... <upstream>'.
++
+This option is useful in the case where one is developing a feature on
+top of an upstream branch. While the feature is being worked on, the
+upstream branch may advance and it may not be the best idea to keep
+rebasing on top of the upstream but to keep the base commit as-is.
++
+Although both this option and --fork-point find the merge base between
+<upstream> and <branch>, this option uses the merge base as the _starting
+point_ on which new commits will be created, whereas --fork-point uses
+the merge base to determine the _set of commits_ which will be rebased.
++
+See also INCOMPATIBLE OPTIONS below.
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
@@ -369,6 +387,10 @@ ends up being empty, the <upstream> will be used as a fallback.
 +
 If either <upstream> or --root is given on the command line, then the
 default is `--no-fork-point`, otherwise the default is `--fork-point`.
++
+If your branch was based on <upstream> but <upstream> was rewound and
+your branch contains commits which were dropped, this option can be used
+with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
 --whitespace=<option>::
@@ -545,6 +567,8 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --rebase-merges
  * --rebase-merges and --strategy
  * --rebase-merges and --strategy-option
+ * --keep-base and --onto
+ * --keep-base and --root
 
 BEHAVIORAL DIFFERENCES
 -----------------------
@@ -870,7 +894,7 @@ NOTE: While an "easy case recovery" sometimes appears to be successful
       --interactive` will be **resurrected**!
 
 The idea is to manually tell 'git rebase' "where the old 'subsystem'
-ended and your 'topic' began", that is, what the old merge-base
+ended and your 'topic' began", that is, what the old merge base
 between them was.  You will have to find a way to name the last commit
 of the old 'subsystem', for example:
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index b78bd92002..1a49060973 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -29,8 +29,8 @@
 #include "rebase-interactive.h"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
@@ -1397,6 +1397,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	struct rebase_options options = REBASE_OPTIONS_INIT;
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
@@ -1415,6 +1416,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
@@ -1568,6 +1571,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		warning(_("git rebase --preserve-merges is deprecated. "
 			  "Use --rebase-merges instead."));
 
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
 	if (action != ACTION_NONE && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
@@ -1903,12 +1913,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index e087c4bf00..71e7159694 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -2030,7 +2030,7 @@ _git_rebase ()
 			--autosquash --no-autosquash
 			--fork-point --no-fork-point
 			--autostash --no-autostash
-			--verify --no-verify
+			--verify --no-verify --keep-base
 			--keep-empty --root --force-rebase --no-ff
 			--rerere-autoupdate
 			--exec
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 2d5c6e641e..78851b9a2a 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase () {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
 test_rebase 'G F E D B A' --fork-point refs/heads/master
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
 test_rebase 'G F C E D B A' refs/heads/master
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index fbedfe7b4a..2f9f82be10 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -75,11 +75,15 @@ test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --keep-base master
+test_rebase_same_head success noop same success noop-force same --keep-base
 test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --keep-base --keep-base master
 
 test_expect_success 'add work same to side' '
 	test_commit E
@@ -91,11 +95,15 @@ test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --keep-base master
+test_rebase_same_head success noop same success noop-force same --keep-base
 test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --fork-point --keep-base master
 
 test_expect_success 'add work same to upstream' '
 	git checkout master &&
@@ -107,8 +115,11 @@ changes='our and their changes'
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success work diff --onto master... master
+test_rebase_same_head success noop same success work diff --keep-base master
+test_rebase_same_head success noop same success work diff --keep-base
 test_rebase_same_head failure work same success work diff --fork-point --onto B B
 test_rebase_same_head failure work same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work diff --fork-point --onto master... master
+test_rebase_same_head success noop same success work diff --fork-point --keep-base master
 
 test_done

diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
new file mode 100755
index 0000000000..2d5c6e641e
--- /dev/null
+++ b/t/t3431-rebase-fork-point.sh
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='git rebase --fork-point test'
+
+. ./test-lib.sh
+
+# A---B---D---E    (master)
+#      \
+#       C*---F---G (side)
+#
+# C was formerly part of master but master was rewound to remove C
+#
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	git branch -t side &&
+	git reset --hard HEAD^ &&
+	test_commit D &&
+	test_commit E &&
+	git checkout side &&
+	test_commit F &&
+	test_commit G
+'
+
+test_rebase () {
+	expected="$1" &&
+	shift &&
+	test_expect_success "git rebase $*" "
+		git checkout master &&
+		git reset --hard E &&
+		git checkout side &&
+		git reset --hard G &&
+		git rebase $* &&
+		test_write_lines $expected >expect &&
+		git log --pretty=%s >actual &&
+		test_cmp expect actual
+	"
+}
+
+test_rebase 'G F E D B A'
+test_rebase 'G F D B A' --onto D
+test_rebase 'G F C E D B A' --no-fork-point
+test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F E D B A' --fork-point refs/heads/master
+test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F C E D B A' refs/heads/master
+test_rebase 'G F C D B A' --onto D refs/heads/master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
new file mode 100755
index 0000000000..f49af274e0
--- /dev/null
+++ b/t/t3432-rebase-fast-forward.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Denton Liu
+#
+
+test_description='ensure rebase fast-forwards commits when possible'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	test_commit C &&
+	test_commit D &&
+	git checkout -t -b side
+'
+
+test_rebase_same_head () {
+	status="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is no-op" "
+		oldhead=\$(git rev-parse HEAD) &&
+		test_when_finished 'git reset --hard \$oldhead' &&
+		git rebase $* &&
+		newhead=\$(git rev-parse HEAD) &&
+		test_cmp_rev \$oldhead \$newhead
+	"
+}
+
+changes='no changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to side' '
+	test_commit E
+'
+
+changes='our changes'
+test_rebase_same_head success
+test_rebase_same_head success master
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head success --onto master... master
+test_rebase_same_head success --no-fork-point
+test_rebase_same_head success --fork-point master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head success --fork-point --onto master... master
+
+test_expect_success 'add work to upstream' '
+	git checkout master &&
+	test_commit F &&
+	git checkout side
+'
+
+changes='our and their changes'
+test_rebase_same_head success --onto B B
+test_rebase_same_head success --onto B... B
+test_rebase_same_head failure --onto master... master
+test_rebase_same_head failure --fork-point --onto B B
+test_rebase_same_head failure --fork-point --onto B... B
+test_rebase_same_head failure --fork-point --onto master... master
+
+test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index f49af274e0..d9f20fa07c 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -18,55 +18,72 @@ test_expect_success setup '
 test_rebase_same_head () {
 	status="$1" &&
 	shift &&
-	test_expect_$status "git rebase $* with $changes is no-op" "
+	what="$1" &&
+	shift &&
+	cmp="$1" &&
+	shift &&
+	test_expect_$status "git rebase $* with $changes is $what" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
-		git rebase $* &&
+		git rebase $* >stdout &&
+		if test $what = work
+		then
+			test_i18ngrep 'rewinding head' stdout
+		elif test $what = noop
+		then
+			test_i18ngrep 'is up to date' stdout
+		fi &&
 		newhead=\$(git rev-parse HEAD) &&
-		test_cmp_rev \$oldhead \$newhead
+		if test $cmp = same
+		then
+			test_cmp_rev \$oldhead \$newhead
+		elif test $cmp = diff
+		then
+			! test_cmp_rev \$oldhead \$newhead
+		fi
 	"
 }
 
 changes='no changes'
-test_rebase_same_head success
-test_rebase_same_head success master
-test_rebase_same_head success --onto B B
-test_rebase_same_head success --onto B... B
-test_rebase_same_head success --onto master... master
-test_rebase_same_head success --no-fork-point
-test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success work same
+test_rebase_same_head success noop same master
+test_rebase_same_head success noop same --onto B B
+test_rebase_same_head success noop same --onto B... B
+test_rebase_same_head success noop same --onto master... master
+test_rebase_same_head success noop same --no-fork-point
+test_rebase_same_head success work same --fork-point master
+test_rebase_same_head failure noop same --fork-point --onto B B
+test_rebase_same_head failure work same --fork-point --onto B... B
+test_rebase_same_head success work same --fork-point --onto master... master
 
-test_expect_success 'add work to side' '
+test_expect_success 'add work same to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success
-test_rebase_same_head success master
-test_rebase_same_head success --onto B B
-test_rebase_same_head success --onto B... B
-test_rebase_same_head success --onto master... master
-test_rebase_same_head success --no-fork-point
-test_rebase_same_head success --fork-point master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head success --fork-point --onto master... master
+test_rebase_same_head success work same
+test_rebase_same_head success noop same master
+test_rebase_same_head success noop same --onto B B
+test_rebase_same_head success noop same --onto B... B
+test_rebase_same_head success noop same --onto master... master
+test_rebase_same_head success noop same --no-fork-point
+test_rebase_same_head success work same --fork-point master
+test_rebase_same_head failure work same --fork-point --onto B B
+test_rebase_same_head failure work same --fork-point --onto B... B
+test_rebase_same_head success work same --fork-point --onto master... master
 
-test_expect_success 'add work to upstream' '
+test_expect_success 'add work same to upstream' '
 	git checkout master &&
 	test_commit F &&
 	git checkout side
 '
 
 changes='our and their changes'
-test_rebase_same_head success --onto B B
-test_rebase_same_head success --onto B... B
-test_rebase_same_head failure --onto master... master
-test_rebase_same_head failure --fork-point --onto B B
-test_rebase_same_head failure --fork-point --onto B... B
-test_rebase_same_head failure --fork-point --onto master... master
+test_rebase_same_head success noop same --onto B B
+test_rebase_same_head success noop same --onto B... B
+test_rebase_same_head failure work same --onto master... master
+test_rebase_same_head failure work same --fork-point --onto B B
+test_rebase_same_head failure work same --fork-point --onto B... B
+test_rebase_same_head failure work same --fork-point --onto master... master
 
 test_done

diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d9f20fa07c..02b2516595 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -16,22 +16,47 @@ test_expect_success setup '
 '
 
 test_rebase_same_head () {
+	status_n="$1" &&
+	shift &&
+	what_n="$1" &&
+	shift &&
+	cmp_n="$1" &&
+	shift &&
+	status_f="$1" &&
+	shift &&
+	what_f="$1" &&
+	shift &&
+	cmp_f="$1" &&
+	shift &&
+	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+}
+
+test_rebase_same_head_ () {
 	status="$1" &&
 	shift &&
 	what="$1" &&
 	shift &&
 	cmp="$1" &&
 	shift &&
-	test_expect_$status "git rebase $* with $changes is $what" "
+	flag="$1"
+	shift &&
+	test_expect_$status "git rebase$flag $* with $changes is $what with $cmp HEAD" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
-		git rebase $* >stdout &&
+		git rebase$flag $* >stdout &&
 		if test $what = work
 		then
+			# Must check this case first, for 'is up to
+			# date, rebase forced[...]rewinding head' cases
 			test_i18ngrep 'rewinding head' stdout
 		elif test $what = noop
 		then
-			test_i18ngrep 'is up to date' stdout
+			test_i18ngrep 'is up to date' stdout &&
+			! test_i18ngrep 'rebase forced' stdout
+		elif test $what = noop-force
+		then
+			test_i18ngrep 'is up to date, rebase forced' stdout
 		fi &&
 		newhead=\$(git rev-parse HEAD) &&
 		if test $cmp = same
@@ -45,32 +70,32 @@ test_rebase_same_head () {
 }
 
 changes='no changes'
-test_rebase_same_head success work same
-test_rebase_same_head success noop same master
-test_rebase_same_head success noop same --onto B B
-test_rebase_same_head success noop same --onto B... B
-test_rebase_same_head success noop same --onto master... master
-test_rebase_same_head success noop same --no-fork-point
-test_rebase_same_head success work same --fork-point master
-test_rebase_same_head failure noop same --fork-point --onto B B
-test_rebase_same_head failure work same --fork-point --onto B... B
-test_rebase_same_head success work same --fork-point --onto master... master
+test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success noop-force same master
+test_rebase_same_head success noop same success noop-force diff --onto B B
+test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success work same success work same --fork-point master
+test_rebase_same_head failure noop same success work diff --fork-point --onto B B
+test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head success work same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success work same
-test_rebase_same_head success noop same master
-test_rebase_same_head success noop same --onto B B
-test_rebase_same_head success noop same --onto B... B
-test_rebase_same_head success noop same --onto master... master
-test_rebase_same_head success noop same --no-fork-point
-test_rebase_same_head success work same --fork-point master
-test_rebase_same_head failure work same --fork-point --onto B B
-test_rebase_same_head failure work same --fork-point --onto B... B
-test_rebase_same_head success work same --fork-point --onto master... master
+test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success noop-force same master
+test_rebase_same_head success noop same success noop-force diff --onto B B
+test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success work same success work same --fork-point master
+test_rebase_same_head failure work same success work diff --fork-point --onto B B
+test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head success work same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to upstream' '
 	git checkout master &&
@@ -79,11 +104,11 @@ test_expect_success 'add work same to upstream' '
 '
 
 changes='our and their changes'
-test_rebase_same_head success noop same --onto B B
-test_rebase_same_head success noop same --onto B... B
-test_rebase_same_head failure work same --onto master... master
-test_rebase_same_head failure work same --fork-point --onto B B
-test_rebase_same_head failure work same --fork-point --onto B... B
-test_rebase_same_head failure work same --fork-point --onto master... master
+test_rebase_same_head success noop same success noop-force diff --onto B B
+test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head failure work same success work diff --onto master... master
+test_rebase_same_head failure work same success work diff --fork-point --onto B B
+test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head failure work same success work diff --fork-point --onto master... master
 
 test_done

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 670096c065..1ddad46126 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1264,20 +1264,25 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 			    struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
-		return 0;
+		goto done;
 
 	merge_bases = get_merge_bases(onto, head);
-	if (merge_bases && !merge_bases->next) {
-		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
-	} else {
+	if (!merge_bases || merge_bases->next) {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
+
+	oidcpy(merge_base, &merge_bases->item->object.oid);
+	if (!oideq(merge_base, &onto->object.oid))
+		goto done;
+
+	res = 1;
+
+done:
 	free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }

builtin/rebase.c, t/t3400-rebase.sh, t/t3404-rebase-interactive.sh, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 1ddad46126..1e1406c8ba 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1260,8 +1260,8 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
 	struct commit_list *merge_bases = NULL;
@@ -1280,6 +1280,17 @@ static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (!upstream)
+		goto done;
+
+	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (!merge_bases || merge_bases->next)
+		goto done;
+
+	if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+		goto done;
+
 	res = 1;
 
 done:
@@ -2027,13 +2038,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * in which case we could fast-forward without replacing the commits
+	 * with new commits recreated by replaying their changes. This
+	 * optimization must not be done if this is an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
+		    &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 80b23fd326..d7c724bea3 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -295,7 +295,7 @@ test_expect_success 'rebase --am and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase --onto init HEAD^ &&
+		test_must_fail git rebase -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 461dd539ff..3cc9052f10 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1058,7 +1058,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git reset --hard &&
 	git checkout conflict-branch &&
 	set_fake_editor &&
-	test_must_fail git rebase --onto HEAD~2 HEAD~ &&
+	test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
 	test_must_fail git rebase --edit-todo &&
 	git rebase --abort
 '
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 02b2516595..d9957e5f1e 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -106,9 +106,9 @@ test_expect_success 'add work same to upstream' '
 changes='our and their changes'
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head failure work same success work diff --onto master... master
+test_rebase_same_head success noop same success work diff --onto master... master
 test_rebase_same_head failure work same success work diff --fork-point --onto B B
 test_rebase_same_head failure work same success work diff --fork-point --onto B... B
-test_rebase_same_head failure work same success work diff --fork-point --onto master... master
+test_rebase_same_head success noop same success work diff --fork-point --onto master... master
 
 test_done

builtin/rebase.c, t/t3432-rebase-fast-forward.sh

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 1e1406c8ba..7ef9095e7c 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1261,6 +1261,7 @@ static int is_linear_history(struct commit *from, struct commit *to)
 }
 
 static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct commit *restrict_revision,
 			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
@@ -1280,6 +1281,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
 	if (!oideq(merge_base, &onto->object.oid))
 		goto done;
 
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+		goto done;
+
 	if (!upstream)
 		goto done;
 
@@ -2042,9 +2046,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * with new commits recreated by replaying their changes. This
 	 * optimization must not be done if this is an interactive rebase.
 	 */
-	if (can_fast_forward(options.onto, options.upstream, &options.orig_head,
-		    &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision) {
+	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+		    &options.orig_head, &merge_base) &&
+	    !is_interactive(&options)) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index d9957e5f1e..fbedfe7b4a 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -70,32 +70,32 @@ test_rebase_same_head_ () {
 }
 
 changes='no changes'
-test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success work same
 test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
 test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success work same success work same --fork-point master
-test_rebase_same_head failure noop same success work diff --fork-point --onto B B
-test_rebase_same_head failure work same success work diff --fork-point --onto B... B
-test_rebase_same_head success work same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --fork-point master
+test_rebase_same_head success noop same success work diff --fork-point --onto B B
+test_rebase_same_head success noop same success work diff --fork-point --onto B... B
+test_rebase_same_head success noop same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to side' '
 	test_commit E
 '
 
 changes='our changes'
-test_rebase_same_head success work same success work same
+test_rebase_same_head success noop same success work same
 test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
 test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success work same success work same --fork-point master
-test_rebase_same_head failure work same success work diff --fork-point --onto B B
-test_rebase_same_head failure work same success work diff --fork-point --onto B... B
-test_rebase_same_head success work same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --fork-point master
+test_rebase_same_head success noop same success work diff --fork-point --onto B B
+test_rebase_same_head success noop same success work diff --fork-point --onto B... B
+test_rebase_same_head success noop same success work same --fork-point --onto master... master
 
 test_expect_success 'add work same to upstream' '
 	git checkout master &&

diff --git a/t/t3421-rebase-topology-linear.sh b/t/t3421-rebase-topology-linear.sh
index 7274dca40b..b847064f91 100755
--- a/t/t3421-rebase-topology-linear.sh
+++ b/t/t3421-rebase-topology-linear.sh
@@ -31,6 +31,16 @@ test_run_rebase success -m
 test_run_rebase success -i
 test_have_prereq !REBASE_P || test_run_rebase success -p
 
+test_expect_success 'setup branches and remote tracking' '
+	git tag -l >tags &&
+	for tag in $(cat tags)
+	do
+		git branch branch-$tag $tag || return 1
+	done &&
+	git remote add origin "file://$PWD" &&
+	git fetch origin
+'
+
 test_run_rebase () {
 	result=$1
 	shift
@@ -57,10 +67,28 @@ test_run_rebase () {
 	"
 }
 test_run_rebase success ''
+test_run_rebase success --fork-point
 test_run_rebase success -m
 test_run_rebase success -i
 test_have_prereq !REBASE_P || test_run_rebase failure -p
 
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* -f rewrites even if remote upstream is an ancestor" "
+		reset_rebase &&
+		git rebase $* -f branch-b branch-e &&
+		! test_cmp_rev branch-e origin/branch-e &&
+		test_cmp_rev branch-b HEAD~2 &&
+		test_linear_range 'd e' branch-b..
+	"
+}
+test_run_rebase success ''
+test_run_rebase success --fork-point
+test_run_rebase success -m
+test_run_rebase success -i
+test_have_prereq !REBASE_P || test_run_rebase success -p
+
 test_run_rebase () {
 	result=$1
 	shift
@@ -71,6 +99,7 @@ test_run_rebase () {
 	"
 }
 test_run_rebase success ''
+test_run_rebase success --fork-point
 test_run_rebase success -m
 test_run_rebase success -i
 test_have_prereq !REBASE_P || test_run_rebase success -p