Add comment lines to patch format

[Nguyen Thai Ngoc Duy <pclouds@gmail.com>]

Hi,

This is just an idea to help spot subtle changes in patch form
(e.g. visible over email). A line starting with '=' (or something
else) is treated like a comment line and ignored by "git apply". We
could use this line to mark special things in the previous line.

One thing is trailing space, like demonstrated in the patch below,
because trailing spaces may be intentional sometimes. But I'd like to
incorporate some word-diff goodness in patch format using this comment
line to spot few/single character addition/removal.

For example, instead of showing

-  "this is a  string"
+  N_("this is a string")

we could show

-  "this is a  string"
=  ..... .. . ^.......
+  N_("this is a string")
=  ^^^..... .. . .......^

If anyone knows a tool with similar feature, I'd greatly appreciate it
(as the Internet taught me, everything I think of is already thought
of/implemented by someone)

-- 8< --
diff --git a/diff.c b/diff.c
index 77edd50..09d8c19 100644
--- a/diff.c
+++ b/diff.c
@@ -1110,6 +1110,30 @@ static void find_lno(const char *line, struct emit_callback *ecbdata)
 	ecbdata->lno_in_postimage = strtol(p + 1, NULL, 10);
 }
 
+static void annotate_line(struct emit_callback *ecbdata,
+			  const char *line, unsigned long len)
+{
+	char *buf, *s;
+	int trailing = 1;
+	if (!isspace(line[len-2]))   
=	.. .......................^^^
+		return;
+	buf = malloc(len);
+	memcpy(buf, line, len);
+	buf[0] = '=';
+	for (s = buf + len - 2; s > buf; s--) {
+		if (trailing && isspace(*s))
+			*s = '^';
+		else
+			trailing = 0;
+		if (!trailing && !isspace(*s))
+			*s = '.';
+	}
+	emit_line(ecbdata->opt,
+		  diff_get_color(ecbdata->color_diff, DIFF_PLAIN),
+		  diff_get_color(ecbdata->color_diff, DIFF_RESET), buf, len);
+	free(buf);
+}
+
 static void fn_out_consume(void *priv, char *line, unsigned long len)
 {
 	struct emit_callback *ecbdata = priv;
@@ -1208,17 +1232,26 @@ static void fn_out_consume(void *priv, char *line, unsigned long len)
 		return;
 	}
 
-	if (line[0] != '+') {
-		const char *color =
-			diff_get_color(ecbdata->color_diff,
-				       line[0] == '-' ? DIFF_FILE_OLD : DIFF_PLAIN);
+	switch (line[0]) {
+	case '-':
 		ecbdata->lno_in_preimage++;
-		if (line[0] == ' ')
-			ecbdata->lno_in_postimage++;
-		emit_line(ecbdata->opt, color, reset, line, len);
-	} else {
+		emit_line(ecbdata->opt,
+			  diff_get_color(ecbdata->color_diff, DIFF_FILE_OLD),
+			  reset, line, len);
+		annotate_line(ecbdata, line, len);
+		break;
+	case '+':
 		ecbdata->lno_in_postimage++;
 		emit_add_line(reset, ecbdata, line + 1, len - 1);
+		annotate_line(ecbdata, line, len);
+		break;
+	case ' ':
+		ecbdata->lno_in_preimage++;
+			ecbdata->lno_in_postimage++;
+		emit_line(ecbdata->opt, plain, reset, line, len);
+		break;
+	default:
+		die("huh? a diff line starting with '%c'??", line[0]);
 	}
 }
 
-- 8< --
-- 
Duy

-- 
Duy