[PATCH 09/14] range-diff: relieve callers of low-level configuration burden

[Eric Sunshine <sunshine@sunshineco.com>]

There are a number of very low-level configuration details which need to
be managed precisely to generate a proper range-diff. In particular,
'diff_options' output format, header suppression, indentation, and
dual-color mode must all be set appropriately to ensure proper behavior.

Handle these details locally in the libified range-diff back-end rather
than forcing each caller to have specialized knowledge of these
implementation details, and to avoid duplication as new callers are
added.

While at it, localize these tweaks to be active only while generating
the range-diff, so they don't clobber the caller-provided
'diff_options', which might be used beyond range-diff generation.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---
 builtin/range-diff.c | 23 ++++-------------------
 range-diff.c         | 24 ++++++++++++++++++++++--
 range-diff.h         |  3 ++-
 3 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/builtin/range-diff.c b/builtin/range-diff.c
index bbe6b05ae9..91463a1df6 100644
--- a/builtin/range-diff.c
+++ b/builtin/range-diff.c
@@ -11,11 +11,6 @@ N_("git range-diff [<options>] <base> <old-tip> <new-tip>"),
 NULL
 };
 
-static struct strbuf *output_prefix_cb(struct diff_options *opt, void *data)
-{
-	return data;
-}
-
 int cmd_range_diff(int argc, const char **argv, const char *prefix)
 {
 	int creation_factor = RANGE_DIFF_CREATION_FACTOR_DEFAULT;
@@ -29,17 +24,11 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 	int i, j, res = 0;
-	struct strbuf four_spaces = STRBUF_INIT;
 	struct strbuf range1 = STRBUF_INIT, range2 = STRBUF_INIT;
 
 	git_config(git_diff_ui_config, NULL);
 
 	diff_setup(&diffopt);
-	diffopt.output_format = DIFF_FORMAT_PATCH;
-	diffopt.flags.suppress_diff_headers = 1;
-	diffopt.output_prefix = output_prefix_cb;
-	strbuf_addstr(&four_spaces, "    ");
-	diffopt.output_prefix_data = &four_spaces;
 
 	argc = parse_options(argc, argv, NULL, options,
 			     builtin_range_diff_usage, PARSE_OPT_KEEP_UNKNOWN);
@@ -55,12 +44,9 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 	argc = j;
 	diff_setup_done(&diffopt);
 
-	if (simple_color < 1) {
-		if (!simple_color)
-			/* force color when --dual-color was used */
-			diffopt.use_color = 1;
-		diffopt.flags.dual_color_diffed_diffs = 1;
-	}
+	/* force color when --dual-color was used */
+	if (!simple_color)
+		diffopt.use_color = 1;
 
 	if (argc == 2) {
 		if (!strstr(argv[0], ".."))
@@ -96,11 +82,10 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 	}
 
 	res = show_range_diff(range1.buf, range2.buf, creation_factor,
-			      &diffopt);
+			      simple_color < 1, &diffopt);
 
 	strbuf_release(&range1);
 	strbuf_release(&range2);
-	strbuf_release(&four_spaces);
 
 	return res;
 }
diff --git a/range-diff.c b/range-diff.c
index 76e053c2b2..091fc344cd 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -414,8 +414,14 @@ static void output(struct string_list *a, struct string_list *b,
 	strbuf_release(&dashes);
 }
 
+static struct strbuf *output_prefix_cb(struct diff_options *opt, void *data)
+{
+	return data;
+}
+
 int show_range_diff(const char *range1, const char *range2,
-		    int creation_factor, struct diff_options *diffopt)
+		    int creation_factor, int dual_color,
+		    struct diff_options *diffopt)
 {
 	int res = 0;
 
@@ -428,9 +434,23 @@ int show_range_diff(const char *range1, const char *range2,
 		res = error(_("could not parse log for '%s'"), range2);
 
 	if (!res) {
+		struct diff_options opts;
+		struct strbuf indent = STRBUF_INIT;
+
+		memcpy(&opts, diffopt, sizeof(opts));
+		opts.output_format = DIFF_FORMAT_PATCH;
+		opts.flags.suppress_diff_headers = 1;
+		opts.flags.dual_color_diffed_diffs = dual_color;
+		opts.output_prefix = output_prefix_cb;
+		strbuf_addstr(&indent, "    ");
+		opts.output_prefix_data = &indent;
+		diff_setup_done(&opts);
+
 		find_exact_matches(&branch1, &branch2);
 		get_correspondences(&branch1, &branch2, creation_factor);
-		output(&branch1, &branch2, diffopt);
+		output(&branch1, &branch2, &opts);
+
+		strbuf_release(&indent);
 	}
 
 	string_list_clear(&branch1, 1);
diff --git a/range-diff.h b/range-diff.h
index 73d6e232fe..bf265594f3 100644
--- a/range-diff.h
+++ b/range-diff.h
@@ -6,6 +6,7 @@
 #define RANGE_DIFF_CREATION_FACTOR_DEFAULT 60
 
 int show_range_diff(const char *range1, const char *range2,
-		    int creation_factor, struct diff_options *diffopt);
+		    int creation_factor, int dual_color,
+		    struct diff_options *diffopt);
 
 #endif
-- 
2.18.0.345.g5c9ce644c3