[PATCH] diff: add diff.srcprefix and diff.dstprefix option support

[Peter Hutterer <peter.hutterer@who-t.net>]

The git option equivalent to --src-prefix and --dst-prefix.
Both of these are of lower precedence than the diff.noprefix and
diff.mnemonicprefix option.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
---
As David already mentioned [1] my main motivation here is to use
a prefix of "./" because that is patch -p1 compatible *and* supports
double-click highlighting of the file path in most terminals.

The current approach of a/ and b/ fail at the latter and diff.noprefix
fails at the former.

[1] https://lore.kernel.org/git/f80aaf4a-ffea-48e6-b279-c3b7a6a53996@ixit.cz/

 Documentation/config/diff.txt |  6 ++++++
 diff.c                        | 18 ++++++++++++++++++
 diff.h                        |  1 +
 t/t4013-diff-various.sh       | 20 ++++++++++++++++++++
 4 files changed, 45 insertions(+)

diff --git a/Documentation/config/diff.txt b/Documentation/config/diff.txt
index 6c7e09a1ef5e..888632955b30 100644
--- a/Documentation/config/diff.txt
+++ b/Documentation/config/diff.txt
@@ -111,6 +111,12 @@ diff.mnemonicPrefix::
 diff.noprefix::
 	If set, 'git diff' does not show any source or destination prefix.
 
+diff.srcprefix::
+	If set, 'git diff' uses this source prefix.
+
+diff.dstprefix::
+	If set, 'git diff' uses this destination prefix.
+
 diff.relative::
 	If set to 'true', 'git diff' does not show changes outside of the directory
 	and show pathnames relative to the current directory.
diff --git a/diff.c b/diff.c
index e50def45383e..52a476737def 100644
--- a/diff.c
+++ b/diff.c
@@ -62,6 +62,8 @@ static const char *diff_order_file_cfg;
 int diff_auto_refresh_index = 1;
 static int diff_mnemonic_prefix;
 static int diff_no_prefix;
+static const char *diff_src_prefix;
+static const char *diff_dst_prefix;
 static int diff_relative;
 static int diff_stat_name_width;
 static int diff_stat_graph_width;
@@ -408,6 +410,12 @@ int git_diff_ui_config(const char *var, const char *value,
 		diff_no_prefix = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "diff.srcprefix")) {
+		return git_config_string(&diff_src_prefix, var, value);
+	}
+	if (!strcmp(var, "diff.dstprefix")) {
+		return git_config_string(&diff_dst_prefix, var, value);
+	}
 	if (!strcmp(var, "diff.relative")) {
 		diff_relative = git_config_bool(var, value);
 		return 0;
@@ -3429,6 +3437,14 @@ void diff_set_default_prefix(struct diff_options *options)
 	options->b_prefix = "b/";
 }
 
+void diff_set_custom_prefix(struct diff_options *options, const char *src_prefix, const char *dst_prefix)
+{
+	if (src_prefix)
+		options->a_prefix = src_prefix;
+	if (dst_prefix)
+		options->b_prefix = dst_prefix;
+}
+
 struct userdiff_driver *get_textconv(struct repository *r,
 				     struct diff_filespec *one)
 {
@@ -4736,6 +4752,8 @@ void repo_diff_setup(struct repository *r, struct diff_options *options)
 		diff_set_noprefix(options);
 	} else if (!diff_mnemonic_prefix) {
 		diff_set_default_prefix(options);
+		if (diff_src_prefix || diff_dst_prefix)
+			diff_set_custom_prefix(options, diff_src_prefix, diff_dst_prefix);
 	}
 
 	options->color_moved = diff_color_moved_default;
diff --git a/diff.h b/diff.h
index 66bd8aeb2936..ab4dd5ec70f3 100644
--- a/diff.h
+++ b/diff.h
@@ -499,6 +499,7 @@ void diff_tree_combined_merge(const struct commit *commit, struct rev_info *rev)
 void diff_set_mnemonic_prefix(struct diff_options *options, const char *a, const char *b);
 void diff_set_noprefix(struct diff_options *options);
 void diff_set_default_prefix(struct diff_options *options);
+void diff_set_custom_prefix(struct diff_options *options, const char *src_prefix, const char *dst_prefix);
 
 int diff_can_quit_early(struct diff_options *);
 
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 1e3b2dbea484..86834186fdba 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -663,6 +663,26 @@ test_expect_success 'diff --default-prefix overrides diff.mnemonicprefix' '
 	check_prefix actual a/file0 b/file0
 '
 
+test_expect_success 'diff respects diff.srcprefix' '
+	git -c diff.srcprefix=x/ diff >actual &&
+	check_prefix actual x/file0 b/file0
+'
+
+test_expect_success 'diff respects diff.dstprefix' '
+	git -c diff.dstprefix=y/ diff >actual &&
+	check_prefix actual a/file0 y/file0
+'
+
+test_expect_success 'diff src/dstprefix ignored with diff.noprefix' '
+	git -c diff.dstprefix=y/ -c diff.srcprefix=x/ -c diff.noprefix diff >actual &&
+	check_prefix actual file0 file0
+'
+
+test_expect_success 'diff src/dstprefix ignored with diff.mnemonicprefix' '
+	git -c diff.dstprefix=x/ -c diff.srcprefix=y/ -c diff.mnemonicprefix diff >actual &&
+	check_prefix actual i/file0 w/file0
+'
+
 test_expect_success 'diff --no-renames cannot be abbreviated' '
 	test_expect_code 129 git diff --no-rename >actual 2>error &&
 	test_must_be_empty actual &&
-- 
2.44.0