[PATCH 1/7] Add a prefix output callback to diff output.

[Bo Yang <struggleyb.nku@gmail.com>]

The callback allow to output some prefix string for
each line of diff output.

Signed-off-by: Bo Yang <struggleyb.nku@gmail.com>
---
 diff.c |   11 ++++++++---
 diff.h |    5 +++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/diff.c b/diff.c
index e49f14a..2a38bef 100644
--- a/diff.c
+++ b/diff.c
@@ -282,11 +282,16 @@ static void check_blank_at_eof(mmfile_t *mf1, mmfile_t *mf2,
 	ecbdata->blank_at_eof_in_postimage = (at - l2) + 1;
 }
 
-static void emit_line_0(FILE *file, const char *set, const char *reset,
+static void emit_line_0(struct diff_options *o, const char *set, const char *reset,
 			int first, const char *line, int len)
 {
 	int has_trailing_newline, has_trailing_carriage_return;
 	int nofirst;
+	FILE *file = o->file;
+
+	if (o->output_prefix) {
+		o->output_prefix(file, 1, o->output_prefix_data);
+	}
 
 	if (len == 0) {
 		has_trailing_newline = (first == '\n');
@@ -316,10 +321,10 @@ static void emit_line_0(FILE *file, const char *set, const char *reset,
 		fputc('\n', file);
 }
 
-static void emit_line(FILE *file, const char *set, const char *reset,
+static void emit_line(struct diff_options *o, const char *set, const char *reset,
 		      const char *line, int len)
 {
-	emit_line_0(file, set, reset, line[0], line+1, len-1);
+	emit_line_0(o, set, reset, line[0], line+1, len-1);
 }
 
 static int new_blank_line_at_eof(struct emit_callback *ecbdata, const char *line, int len)
diff --git a/diff.h b/diff.h
index 6a71013..0031dd8 100644
--- a/diff.h
+++ b/diff.h
@@ -9,6 +9,7 @@
 struct rev_info;
 struct diff_options;
 struct diff_queue_struct;
+struct strbuf;
 
 typedef void (*change_fn_t)(struct diff_options *options,
 		 unsigned old_mode, unsigned new_mode,
@@ -25,6 +26,8 @@ typedef void (*add_remove_fn_t)(struct diff_options *options,
 typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
 		struct diff_options *options, void *data);
 
+typedef struct strbuf *(*diff_prefix_fn_t)(FILE *file, int print, void *data);
+
 #define DIFF_FORMAT_RAW		0x0001
 #define DIFF_FORMAT_DIFFSTAT	0x0002
 #define DIFF_FORMAT_NUMSTAT	0x0004
@@ -122,6 +125,8 @@ struct diff_options {
 	add_remove_fn_t add_remove;
 	diff_format_fn_t format_callback;
 	void *format_callback_data;
+	diff_prefix_fn_t output_prefix;
+	void *output_prefix_data;
 };
 
 enum color_diff {
-- 
1.7.1.94.gc3269