[PATCH 2/2] format-patch: handle range-diff on notes correctly for single patches

[kristofferhaugsbakk@fastmail.com]

From: Kristoffer Haugsbakk <code@khaugsbakk.name>

No `--[no-]notes` options are sent to the range-diff subprocess in
`range-diff.c` when making a single patch.  This means that you can get
different Git notes below the commit message and in the range-diff
part.  (See the previous commit for elaboration.)

Use the struct member that we introduced and populated in the
previous commit.

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
---

Notes (series):
    I’ve tried to conform to 6caa96c2 (t3206: test_when_finished before
    dirtying operations, not after, 2024-08-06) in the test here.

 log-tree.c            |  3 ++-
 t/t3206-range-diff.sh | 16 +++++++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/log-tree.c b/log-tree.c
index 73d21f71764..831284288f9 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -718,7 +718,8 @@ static void show_diff_of_diff(struct rev_info *opt)
 			.creation_factor = opt->creation_factor,
 			.dual_color = 1,
 			.max_memory = RANGE_DIFF_MAX_MEMORY_DEFAULT,
-			.diffopt = &opts
+			.diffopt = &opts,
+			.other_arg = &opt->rdiff_other_arg
 		};
 
 		memcpy(&dq, &diff_queued_diff, sizeof(diff_queued_diff));
diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
index e091df6d01d..1e812df806b 100755
--- a/t/t3206-range-diff.sh
+++ b/t/t3206-range-diff.sh
@@ -707,7 +707,7 @@ test_expect_success 'format-patch --range-diff does not compare notes by default
 	! grep "note" 0000-*
 '
 
-test_expect_success 'format-patch --notes=custom --range-diff only compares custom notes' '
+test_expect_success 'format-patch --notes=custom --range-diff --cover-letter only compares custom notes' '
 	test_when_finished "git notes remove topic unmodified || :" &&
 	git notes add -m "topic note" topic &&
 	git notes add -m "unmodified note" unmodified &&
@@ -721,6 +721,20 @@ test_expect_success 'format-patch --notes=custom --range-diff only compares cust
 	! grep "## Notes ##" 0000-*
 '
 
+# --range-diff on a single commit requires --no-cover-letter
+test_expect_success 'format-patch --notes=custom --range-diff on single commit only compares custom notes' '
+	test_when_finished "git notes remove HEAD unmodified || :" &&
+	git notes add -m "topic note" HEAD &&
+	test_when_finished "git notes --ref=custom remove HEAD unmodified || :" &&
+	git notes add -m "unmodified note" unmodified &&
+	git notes --ref=custom add -m "topic note (custom)" HEAD &&
+	git notes --ref=custom add -m "unmodified note (custom)" unmodified &&
+	git format-patch --notes=custom --range-diff=$prev \
+		-1 --stdout >actual &&
+	test_grep "## Notes (custom) ##" actual &&
+	test_grep ! "## Notes ##" actual
+'
+
 test_expect_success 'format-patch --range-diff with --no-notes' '
 	test_when_finished "git notes remove topic unmodified || :" &&
 	git notes add -m "topic note" topic &&
-- 
2.51.0.270.gdb73cbc1bc1