diff: handle diffstat of rewritten binary files

The logic in builtin_diffstat assumes that a
complete_rewrite pair should have its lines counted. This is
nonsensical for binary files and leads to confusing things
like:

  $ git diff --stat --summary HEAD^ HEAD
   foo.rand |  Bin 4096 -> 4096 bytes
   1 files changed, 0 insertions(+), 0 deletions(-)

  $ git diff --stat --summary -B HEAD^ HEAD
   foo.rand |   34 +++++++++++++++-------------------
   1 files changed, 15 insertions(+), 19 deletions(-)
   rewrite foo.rand (100%)

So let's reorder the function to handle binary files first
(which from diffstat's perspective look like complete
rewrites anyway), then rewrites, then actual diffstats.

There are two bonus prizes to this reorder:

  1. It gets rid of a now-superfluous goto.

  2. The binary case is at the top, which means we can
     further optimize it in the next patch.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -1811,34 +1811,38 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 		data->is_unmerged = 1;
 		return;
 	}
-	if (complete_rewrite) {
+
+	if (diff_filespec_is_binary(one) || diff_filespec_is_binary(two)) {
+		if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0)
+			die("unable to read files to diff");
+		data->is_binary = 1;
+		data->added = mf2.size;
+		data->deleted = mf1.size;
+	}
+
+	else if (complete_rewrite) {
 		diff_populate_filespec(one, 0);
 		diff_populate_filespec(two, 0);
 		data->deleted = count_lines(one->data, one->size);
 		data->added = count_lines(two->data, two->size);
-		goto free_and_return;
 	}
-	if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0)
-		die("unable to read files to diff");
 
-	if (diff_filespec_is_binary(one) || diff_filespec_is_binary(two)) {
-		data->is_binary = 1;
-		data->added = mf2.size;
-		data->deleted = mf1.size;
-	} else {
+	else {
 		/* Crazy xdl interfaces.. */
 		xpparam_t xpp;
 		xdemitconf_t xecfg;
 		xdemitcb_t ecb;
 
+		if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0)
+			die("unable to read files to diff");
+
 		memset(&xpp, 0, sizeof(xpp));
 		memset(&xecfg, 0, sizeof(xecfg));
 		xpp.flags = XDF_NEED_MINIMAL | o->xdl_opts;
 		xdi_diff_outf(&mf1, &mf2, diffstat_consume, diffstat,
 			      &xpp, &xecfg, &ecb);
 	}
 
- free_and_return:
 	diff_free_filespec_data(one);
 	diff_free_filespec_data(two);
 }

t/t4031-diff-rewrite-binary.sh

@@ -44,6 +44,13 @@ test_expect_success 'rewrite diff can show binary patch' '
 	grep "GIT binary patch" diff
 '
 
+test_expect_success 'rewrite diff --stat shows binary changes' '
+	git diff -B --stat --summary >diff &&
+	grep "Bin" diff &&
+	grep "0 insertions.*0 deletions" diff &&
+	grep " rewrite file" diff
+'
+
 {
 	echo "#!$SHELL_PATH"
 	cat <<'EOF'