rebase: add documentation and test for --no-rebase-merges

As far as I can tell, --no-rebase-merges has always worked, but has
never been documented. It is especially important to document it before
a rebase.rebaseMerges option is introduced so that users know how to
override the config option on the command line. It's also important to
clarify that --rebase-merges without an argument is not the same as
--no-rebase-merges and not passing --rebase-merges is not the same as
passing --rebase-merges=no-rebase-cousins.

A test case is necessary to make sure that --no-rebase-merges keeps
working after its code is refactored in the following patches of this
series. The test case is a little contrived: It's unlikely that a user
would type both --rebase-merges and --no-rebase-merges at the same time.
However, if an alias is defined which includes --rebase-merges, the user
might decide to add --no-rebase-merges to countermand that part of the
alias but leave alone other flags set by the alias.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index fa2a06c19f..d46d9545f2 100755
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -250,6 +250,16 @@ test_expect_success 'with a branch tip that was cherry-picked already' '
 	EOF
 '
 
+test_expect_success '--no-rebase-merges countermands --rebase-merges' '
+	git checkout -b no-rebase-merges E &&
+	git rebase --rebase-merges --no-rebase-merges C &&
+	test_cmp_graph C.. <<-\EOF
+	* B
+	* D
+	o C
+	EOF
+'
+
 test_expect_success 'do not rebase cousins unless asked for' '
 	git checkout -b cousins main &&
 	before="$(git rev-parse --verify HEAD)" &&