[PATCH 2/2] format-patch: don't include --stat with --range-diff output

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Fix a regression introduced in my a48e12ef7a ("range-diff: make diff
option behavior (e.g. --stat) consistent", 2018-11-13). Since the
format-patch setup code implicitly sets --stat --summary by default,
we started emitting the --stat output in the cover letter's
range-diff.

As noted in df569c3f31 ("range-diff doc: add a section about output
stability", 2018-11-09) the --stat output is currently rather useless,
and just adds noise.

Perhaps we should detect if --stat or --summary were implicitly passed
to format-patch, and then pass them along, but I think fixing it this
way is fine. If our --stat output ever becomes useful in range-diff we
can revisit this.

There's still cases like e.g. --numstat triggering rather useless
range-diff output, but I think it's OK to just handle the default
case. Users are unlikely to produce a formatted patch with the likes
of --numstat, or indeed any other custom diff option except -U<n> or
maybe -W. If they need weirder combinations of options they can always
manually produce the range-diff.

This whole situation comes about because we're assuming that when the
user passes along e.g. -U10 that they want that some 10-line context
for the range-diff as for the patches themselves. As noted in [1] I
think it's worth re-visiting this and making -U10 just apply to the
patches, and e.g. --range-diff-U10 to the range-diff. But that's left
as a topic for another series less close to a rc2.

1. https://public-inbox.org/git/87d0ri7gbs.fsf@evledraar.gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/log.c         |  7 ++++++-
 t/t3206-range-diff.sh | 12 ------------
 2 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/builtin/log.c b/builtin/log.c
index 0fe6f9ba1e..7cd2db0be9 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1094,9 +1094,13 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 	}
 
 	if (rev->rdiff1) {
+		struct diff_options opts;
+		memcpy(&opts, &rev->diffopt, sizeof(opts));
+		opts.output_format &= ~(DIFF_FORMAT_DIFFSTAT | DIFF_FORMAT_SUMMARY);
+
 		fprintf_ln(rev->diffopt.file, "%s", rev->rdiff_title);
 		show_range_diff(rev->rdiff1, rev->rdiff2,
-				rev->creation_factor, 1, &rev->diffopt);
+				rev->creation_factor, 1, &opts);
 	}
 }
 
@@ -1697,6 +1701,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	if (!use_patch_format &&
 		(!rev.diffopt.output_format ||
 		 rev.diffopt.output_format == DIFF_FORMAT_PATCH))
+		/* Needs to be mirrored in show_range_diff() invocation */
 		rev.diffopt.output_format = DIFF_FORMAT_DIFFSTAT | DIFF_FORMAT_SUMMARY;
 	if (!rev.diffopt.stat_width)
 		rev.diffopt.stat_width = MAIL_DEFAULT_WRAP;
diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
index 0235c038be..90def330bd 100755
--- a/t/t3206-range-diff.sh
+++ b/t/t3206-range-diff.sh
@@ -252,21 +252,9 @@ do
 			master..unmodified >actual.raw &&
 		sed -e "s|^:||" -e "s|:$||" >expect <<-\EOF &&
 		:1:  4de457d = 1:  35b9b25 s/5/A/
-		:     a => b | 0
-		:     1 file changed, 0 insertions(+), 0 deletions(-)
-		:    :
 		:2:  fccce22 = 2:  de345ab s/4/A/
-		:     a => b | 0
-		:     1 file changed, 0 insertions(+), 0 deletions(-)
-		:    :
 		:3:  147e64e = 3:  9af6654 s/11/B/
-		:     a => b | 0
-		:     1 file changed, 0 insertions(+), 0 deletions(-)
-		:    :
 		:4:  a63e992 = 4:  2901f77 s/12/B/
-		:     a => b | 0
-		:     1 file changed, 0 insertions(+), 0 deletions(-)
-		:    :
 		:-- :
 		EOF
 		sed -ne "/^1:/,/^--/p" <actual.raw >actual &&
-- 
2.20.0.rc0.387.gc7a69e6b6c