@@ -1349,6 +1370,31 @@ static int try_to_commit(struct repository *r,
 		commit_list_insert(current_head, &parents);
 	}

+	if (opts->committer_date_is_author_date) {
+		struct ident_split ident;
+		struct strbuf date = STRBUF_INIT;
+
+		if (split_ident_line(&ident, author, (int)strlen(author)) < 0) {
+			res = error(_("malformed ident line '%s'"), author);
+			goto out;
+		}
+		if (!ident.date_begin) {
+			res = error(_("corrupted author without date information"));
+			goto out;
+		}
+
+		strbuf_addf(&date, "@%.*s %.*s",
+			    (int)(ident.date_end - ident.date_begin),
+			    ident.date_begin,
+			    (int)(ident.tz_end - ident.tz_begin),
+			    ident.tz_begin);
+		res = setenv("GIT_COMMITTER_DATE", date.buf, 1);

+		strbuf_release(&date);
+
+		if (res)
+			goto out;
+	}
+
 	if (write_index_as_tree(&tree, r->index, r->index_file, 0, NULL)) {
 		res = error(_("git write-tree failed to write a tree"));
 		goto out;

@@ -2532,6 +2578,11 @@ static int read_populate_opts(struct replay_opts *opts)
 			opts->signoff = 1;
 		}

+		if (file_exists(rebase_path_cdate_is_adate())) {
+			opts->allow_ff = 0;
+			opts->committer_date_is_author_date = 1;
+		}
+
 		if (file_exists(rebase_path_reschedule_failed_exec()))
 			opts->reschedule_failed_exec = 1;

@@ -2622,6 +2673,8 @@ int write_basic_state(struct replay_opts *opts, const char *head_name,
 		write_file(rebase_path_drop_redundant_commits(), "%s", "");
 	if (opts->keep_redundant_commits)
 		write_file(rebase_path_keep_redundant_commits(), "%s", "");
+	if (opts->committer_date_is_author_date)
+		write_file(rebase_path_cdate_is_adate(), "%s", "");
 	if (opts->reschedule_failed_exec)
 		write_file(rebase_path_reschedule_failed_exec(), "%s", "");

@@ -3542,6 +3595,10 @@ static int do_merge(struct repository *r,
 			goto leave_merge;
 		}

+		if (opts->committer_date_is_author_date)
+			argv_array_pushf(&cmd.env_array, "GIT_COMMITTER_DATE=%s",
+					 author_date_from_env_array(&cmd.env_array));
+
 		cmd.git_cmd = 1;
 		argv_array_push(&cmd.args, "merge");
 		argv_array_push(&cmd.args, "-s");

@@ -3819,7 +3876,8 @@ static int pick_commits(struct repository *r,
 	setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
 	if (opts->allow_ff)
 		assert(!(opts->signoff || opts->no_commit ||
-				opts->record_origin || opts->edit));
+				opts->record_origin || opts->edit ||
+				opts->committer_date_is_author_date));
 	if (read_and_refresh_cache(r, opts))
 		return -1;

diff --git a/sequencer.h b/sequencer.h
index 0bee85093e..4ab94119ae 100644
--- a/sequencer.h
+++ b/sequencer.h

@@ -45,6 +45,7 @@ struct replay_opts {
 	int verbose;
 	int quiet;
 	int reschedule_failed_exec;
+	int committer_date_is_author_date;

 	int mainline;

diff --git a/t/t3422-rebase-incompatible-options.sh b/t/t3422-rebase-incompatible-options.sh
index 55ca46786d..c8234062c6 100755
--- a/t/t3422-rebase-incompatible-options.sh
+++ b/t/t3422-rebase-incompatible-options.sh

@@ -61,7 +61,6 @@ test_rebase_am_only () {
 }

 test_rebase_am_only --whitespace=fix
-test_rebase_am_only --committer-date-is-author-date
 test_rebase_am_only -C4

 test_expect_success REBASE_P '--preserve-merges incompatible with --signoff' '

diff --git a/t/t3436-rebase-more-options.sh b/t/t3436-rebase-more-options.sh
index 4f8a6e51c9..50a63d8ebe 100755
--- a/t/t3436-rebase-more-options.sh
+++ b/t/t3436-rebase-more-options.sh

@@ -9,6 +9,9 @@ test_description='tests to ensure compatibility between am and interactive backe

 . "$TEST_DIRECTORY"/lib-rebase.sh

+GIT_AUTHOR_DATE="1999-04-02T08:03:20+05:30"
+export GIT_AUTHOR_DATE
+
 # This is a special case in which both am and interactive backends
 # provide the same output. It was done intentionally because
 # both the backends fall short of optimal behaviour.

@@ -21,11 +24,20 @@ test_expect_success 'setup' '
 	test_write_lines "line 1" "new line 2" "line 3" >file &&
 	git commit -am "update file" &&
 	git tag side &&
+	test_commit commit1 foo foo1 &&
+	test_commit commit2 foo foo2 &&
+	test_commit commit3 foo foo3 &&

 	git checkout --orphan master &&
+	rm foo &&
 	test_write_lines "line 1" "        line 2" "line 3" >file &&
 	git commit -am "add file" &&
-	git tag main
+	git tag main &&
+
+	mkdir test-bin &&
+	write_script test-bin/git-merge-test <<-\EOF
+	exec git-merge-recursive "$@"
+	EOF
 '

 test_expect_success '--ignore-whitespace works with apply backend' '

@@ -52,6 +64,50 @@ test_expect_success '--ignore-whitespace is remembered when continuing' '
 	git diff --exit-code side
 '

+test_ctime_is_atime () {
+	git log $1 --format=%ai >authortime &&
+	git log $1 --format=%ci >committertime &&
+	test_cmp authortime committertime
+}
+
+test_expect_success '--committer-date-is-author-date works with apply backend' '
+	GIT_AUTHOR_DATE="@1234 +0300" git commit --amend --reset-author &&
+	git rebase --apply --committer-date-is-author-date HEAD^ &&
+	test_ctime_is_atime -1
+'
+
+test_expect_success '--committer-date-is-author-date works with merge backend' '
+	GIT_AUTHOR_DATE="@1234 +0300" git commit --amend --reset-author &&
+	git rebase -m --committer-date-is-author-date HEAD^ &&
+	test_ctime_is_atime -1
+'
+
+test_expect_success '--committer-date-is-author-date works with rebase -r' '
+	git checkout side &&
+	GIT_AUTHOR_DATE="@1234 +0300" git merge --no-ff commit3 &&
+	git rebase -r --root --committer-date-is-author-date &&
+	test_ctime_is_atime
+'
+
+test_expect_success '--committer-date-is-author-date works when forking merge' '
+	git checkout side &&
+	GIT_AUTHOR_DATE="@1234 +0300" git merge --no-ff commit3 &&
+	PATH="./test-bin:$PATH" git rebase -r --root --strategy=test \
+					--committer-date-is-author-date &&
+	test_ctime_is_atime
+'
+
+test_expect_success '--committer-date-is-author-date works when committing conflict resolution' '
+	git checkout commit2 &&
+	GIT_AUTHOR_DATE="@1980 +0000" git commit --amend --only --reset-author &&
+	test_must_fail git rebase -m --committer-date-is-author-date \
+		--onto HEAD^^ HEAD^ &&
+	echo resolved > foo &&
+	git add foo &&
+	git rebase --continue &&
+	test_ctime_is_atime -1
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
 	test_editor_unchanged
--

2.27.0