[PATCH] diff: add config option relative

[Laurent Arnoud <laurent@spkdev.net>]

The `diff.relative` boolean option set to `true` to show only changes on the
current directory and show relative pathnames.

Signed-off-by: Laurent Arnoud <laurent@spkdev.net>
---
 Documentation/config/diff.txt   |  4 +++
 diff.c                          |  7 +++++
 t/t9904-diff-relative-config.sh | 48 +++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)
 create mode 100755 t/t9904-diff-relative-config.sh

diff --git Documentation/config/diff.txt Documentation/config/diff.txt
index ff09f1cf73..1d311358d8 100644
--- Documentation/config/diff.txt
+++ Documentation/config/diff.txt
@@ -105,6 +105,10 @@ diff.mnemonicPrefix::
 diff.noprefix::
 	If set, 'git diff' does not show any source or destination prefix.
 
+diff.relative::
+	If set to "true", 'git diff' does not show changes outside of the directory
+	and show pathnames relative.
+
 diff.orderFile::
 	File indicating how to order files within a diff.
 	See the '-O' option to linkgit:git-diff[1] for details.
diff --git diff.c diff.c
index d1ad6a3c4a..24b7a0ae08 100644
--- diff.c
+++ diff.c
@@ -48,6 +48,7 @@ static const char *diff_order_file_cfg;
 int diff_auto_refresh_index = 1;
 static int diff_mnemonic_prefix;
 static int diff_no_prefix;
+static int diff_relative;
 static int diff_stat_graph_width;
 static int diff_dirstat_permille_default = 30;
 static struct diff_options default_diff_options;
@@ -386,6 +387,10 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
 		diff_no_prefix = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "diff.relative")) {
+		diff_relative = git_config_bool(var, value);
+		return 0;
+	}
 	if (!strcmp(var, "diff.statgraphwidth")) {
 		diff_stat_graph_width = git_config_int(var, value);
 		return 0;
@@ -4558,6 +4563,8 @@ void repo_diff_setup(struct repository *r, struct diff_options *options)
 		options->b_prefix = "b/";
 	}
 
+	options->flags.relative_name = diff_relative;
+
 	options->color_moved = diff_color_moved_default;
 	options->color_moved_ws_handling = diff_color_moved_ws_default;
 
diff --git t/t9904-diff-relative-config.sh t/t9904-diff-relative-config.sh
new file mode 100755
index 0000000000..a92d53ca25
--- /dev/null
+++ t/t9904-diff-relative-config.sh
@@ -0,0 +1,48 @@
+#!/bin/sh
+
+test_description='config diff.relative'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	git commit --allow-empty -m empty &&
+	echo content >file1 &&
+	mkdir subdir &&
+	echo other content >subdir/file2 &&
+	git add . &&
+	git commit -m one
+'
+
+check_diff () {
+	dir=$1
+	shift
+	expect=$1
+	shift
+	relative_opt=$1
+	shift
+	short_blob=$(git rev-parse --short "$(git hash-object subdir/file2)")
+	cat >expected <<-EOF
+	diff --git a/$expect b/$expect
+	new file mode 100644
+	index 0000000..$short_blob
+	--- /dev/null
+	+++ b/$expect
+	@@ -0,0 +1 @@
+	+other content
+	EOF
+	test_expect_success "-p $*" "
+		test_config -C $dir diff.relative $relative_opt &&
+		git -C '$dir' diff -p $* HEAD^ >actual &&
+		test_cmp expected actual
+	"
+}
+
+check_diff . file2 false --relative=subdir/
+check_diff . file2 false --relative=subdir
+check_diff . file2 true --relative=subdir/
+check_diff . file2 true --relative=subdir
+check_diff subdir file2 false --relative
+check_diff subdir file2 true --relative
+check_diff subdir file2 true
+
+test_done
-- 
2.26.2