Merge branch 'ph/diff-src-dst-prefix-config'

"git diff" and friends learned two extra configuration variables,
diff.srcPrefix and diff.dstPrefix.

* ph/diff-src-dst-prefix-config:
  diff.*Prefix: use camelCase in the doc and test titles
  diff: add diff.srcPrefix and diff.dstPrefix configuration variables

Documentation/config/diff.txt

@@ -108,9 +108,15 @@ diff.mnemonicPrefix::
 `git diff --no-index a b`;;
 	compares two non-git things (1) and (2).
 
-diff.noprefix::
+diff.noPrefix::
 	If set, 'git diff' does not show any source or destination prefix.
 
+diff.srcPrefix::
+	If set, 'git diff' uses this source prefix. Defaults to "a/".
+
+diff.dstPrefix::
+	If set, 'git diff' uses this destination prefix. Defaults to "b/".
+
 diff.relative::
 	If set to 'true', 'git diff' does not show changes outside of the directory
 	and show pathnames relative to the current directory.

Documentation/diff-options.txt

@@ -865,8 +865,9 @@ endif::git-format-patch[]
 
 --default-prefix::
 	Use the default source and destination prefixes ("a/" and "b/").
-	This is usually the default already, but may be used to override
+	This overrides configuration variables such as `diff.noprefix`,
-	config such as `diff.noprefix`.
+	`diff.srcPrefix`, `diff.dstPrefix`, and `diff.mnemonicPrefix`
+	(see `git-config`(1)).
 
 --line-prefix=<prefix>::
 	Prepend an additional prefix to every line of output.

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 = "a/";
+static const char *diff_dst_prefix = "b/";
 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;
@@ -3425,8 +3433,8 @@ void diff_set_noprefix(struct diff_options *options)
 
 void diff_set_default_prefix(struct diff_options *options)
 {
-	options->a_prefix = "a/";
+	options->a_prefix = diff_src_prefix;
-	options->b_prefix = "b/";
+	options->b_prefix = diff_dst_prefix;
 }
 
 struct userdiff_driver *get_textconv(struct repository *r,
@@ -5362,6 +5370,8 @@ static int diff_opt_default_prefix(const struct option *opt,
 
 	BUG_ON_OPT_NEG(unset);
 	BUG_ON_OPT_ARG(optarg);
+	diff_src_prefix = "a/";
+	diff_dst_prefix = "b/";
 	diff_set_default_prefix(options);
 	return 0;
 }

t/t4013-diff-various.sh

@@ -633,8 +633,8 @@ check_prefix () {
 	test_cmp expect actual.paths
 }
 
-test_expect_success 'diff-files does not respect diff.noprefix' '
+test_expect_success 'diff-files does not respect diff.noPrefix' '
-	git -c diff.noprefix diff-files -p >actual &&
+	git -c diff.noPrefix diff-files -p >actual &&
 	check_prefix actual a/file0 b/file0
 '
 
@@ -643,23 +643,58 @@ test_expect_success 'diff-files respects --no-prefix' '
 	check_prefix actual file0 file0
 '
 
-test_expect_success 'diff respects diff.noprefix' '
+test_expect_success 'diff respects diff.noPrefix' '
-	git -c diff.noprefix diff >actual &&
+	git -c diff.noPrefix diff >actual &&
 	check_prefix actual file0 file0
 '
 
-test_expect_success 'diff --default-prefix overrides diff.noprefix' '
+test_expect_success 'diff --default-prefix overrides diff.noPrefix' '
-	git -c diff.noprefix diff --default-prefix >actual &&
+	git -c diff.noPrefix diff --default-prefix >actual &&
 	check_prefix actual a/file0 b/file0
 '
 
-test_expect_success 'diff respects diff.mnemonicprefix' '
+test_expect_success 'diff respects diff.mnemonicPrefix' '
-	git -c diff.mnemonicprefix diff >actual &&
+	git -c diff.mnemonicPrefix diff >actual &&
 	check_prefix actual i/file0 w/file0
 '
 
-test_expect_success 'diff --default-prefix overrides diff.mnemonicprefix' '
+test_expect_success 'diff --default-prefix overrides diff.mnemonicPrefix' '
-	git -c diff.mnemonicprefix diff --default-prefix >actual &&
+	git -c diff.mnemonicPrefix diff --default-prefix >actual &&
+	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-prefix overrides diff.srcPrefix' '
+	git -c diff.srcPrefix=y/ diff --src-prefix=z/ >actual &&
+	check_prefix actual z/file0 b/file0
+'
+
+test_expect_success 'diff --dst-prefix overrides diff.dstPrefix' '
+	git -c diff.dstPrefix=y/ diff --dst-prefix=z/ >actual &&
+	check_prefix actual a/file0 z/file0
+'
+
+test_expect_success 'diff.{src,dst}Prefix 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,dst}Prefix 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.{src,dst}Prefix ignored with --default-prefix' '
+	git -c diff.dstPrefix=x/ -c diff.srcPrefix=y/ diff --default-prefix >actual &&
 	check_prefix actual a/file0 b/file0
 '