diff --shortstat --dirstat: remove duplicate output

When --shortstat is used in conjunction with --dirstat=changes, git diff will
output the dirstat information twice: first as calculated by the 'lines'
algorithm, then as calculated by the 'changes' algorithm:

    $ git diff --dirstat=changes,10 --shortstat v2.2.0..v2.2.1
     23 files changed, 453 insertions(+), 54 deletions(-)
      33.5% Documentation/RelNotes/
      26.2% t/
      46.6% Documentation/RelNotes/
      16.6% t/

The same duplication happens for --shortstat together with --dirstat=files, but
not for --shortstat together with --dirstat=lines.

Limit output to only include one dirstat part, calculated as specified
by the --dirstat parameter. Also, add test for this.

Signed-off-by: Mårten Kongstad <marten.kongstad@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -4528,7 +4528,7 @@ void diff_flush(struct diff_options *options)
 			show_stats(&diffstat, options);
 		if (output_format & DIFF_FORMAT_SHORTSTAT)
 			show_shortstats(&diffstat, options);
-		if (output_format & DIFF_FORMAT_DIRSTAT)
+		if (output_format & DIFF_FORMAT_DIRSTAT && dirstat_by_line)
 			show_dirstat_by_line(&diffstat, options);
 		free_diffstat_info(&diffstat);
 		separator++;

t/t4047-diff-dirstat.sh

@@ -973,4 +973,18 @@ test_expect_success 'diff.dirstat=future_param,0,lines should warn, but still wo
 	test_i18ngrep -q "diff\\.dirstat" actual_error
 '
 
+test_expect_success '--shortstat --dirstat should output only one dirstat' '
+	git diff --shortstat --dirstat=changes HEAD^..HEAD >out &&
+	grep " dst/copy/changed/$" out >actual_diff_shortstat_dirstat_changes &&
+	test_line_count = 1 actual_diff_shortstat_dirstat_changes &&
+
+	git diff --shortstat --dirstat=lines HEAD^..HEAD >out &&
+	grep " dst/copy/changed/$" out >actual_diff_shortstat_dirstat_lines &&
+	test_line_count = 1 actual_diff_shortstat_dirstat_lines &&
+
+	git diff --shortstat --dirstat=files HEAD^..HEAD >out &&
+	grep " dst/copy/changed/$" out >actual_diff_shortstat_dirstat_files &&
+	test_line_count = 1 actual_diff_shortstat_dirstat_files
+'
+
 test_done