[PATCH 6/6] combine-diff: treat --dirstat like --stat

[Jeff King <peff@peff.net>]

Currently "--cc --dirstat" will show nothing for a merge.  Like
--shortstat and --summary in the previous two patches, it probably makes
sense to treat it like we do --stat, and show a stat against the
first-parent.

This case is less obviously correct than for --shortstat and --summary,
as those are basically variants of --stat themselves. It's possible we
could develop a multi-parent combined dirstat format, in which case we
might regret defining this first-parent behavior. But the same could be
said for --stat, and in the 12+ years of it showing first-parent stats,
nobody has complained.

So showing the first-parent dirstat is at least _useful_, and if we
later develop a clever multi-parent stat format, we'd probably have to
deal with --stat anyway.

Signed-off-by: Jeff King <peff@peff.net>
---
 combine-diff.c                                   | 1 +
 t/t4013-diff-various.sh                          | 1 +
 t/t4013/diff.diff_--dirstat_--cc_master~1_master | 3 +++
 3 files changed, 5 insertions(+)
 create mode 100644 t/t4013/diff.diff_--dirstat_--cc_master~1_master

diff --git a/combine-diff.c b/combine-diff.c
index f42b41d884..23d8fabe75 100644
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -1327,6 +1327,7 @@ static const char *path_path(void *obj)
 #define STAT_FORMAT_MASK (DIFF_FORMAT_NUMSTAT \
 			  | DIFF_FORMAT_SHORTSTAT \
 			  | DIFF_FORMAT_SUMMARY \
+			  | DIFF_FORMAT_DIRSTAT \
 			  | DIFF_FORMAT_DIFFSTAT)
 
 /* find set of paths that every parent touches */
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index e28953975b..9f8f0e84ad 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -358,6 +358,7 @@ diff --line-prefix=abc master master^ side
 diff --dirstat master~1 master~2
 diff --dirstat initial rearrange
 diff --dirstat-by-file initial rearrange
+diff --dirstat --cc master~1 master
 # No-index --abbrev and --no-abbrev
 diff --raw initial
 :noellipses diff --raw initial
diff --git a/t/t4013/diff.diff_--dirstat_--cc_master~1_master b/t/t4013/diff.diff_--dirstat_--cc_master~1_master
new file mode 100644
index 0000000000..fba4e34175
--- /dev/null
+++ b/t/t4013/diff.diff_--dirstat_--cc_master~1_master
@@ -0,0 +1,3 @@
+$ git diff --dirstat --cc master~1 master
+  40.0% dir/
+$
-- 
2.20.1.842.g8986705066