utf8.c: add utf8_strnwidth() with the ability to skip ansi sequences

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

utf8.c

@@ -266,18 +266,26 @@ int utf8_width(const char **start, size_t *remainder_p)
  * string, assuming that the string is utf8.  Returns strlen() instead
  * if the string does not look like a valid utf8 string.
  */
-int utf8_strwidth(const char *string)
+int utf8_strnwidth(const char *string, int len, int skip_ansi)
 {
 	int width = 0;
 	const char *orig = string;
 
-	while (1) {
-		if (!string)
-			return strlen(orig);
-		if (!*string)
-			return width;
+	if (len == -1)
+		len = strlen(string);
+	while (string && string < orig + len) {
+		int skip;
+		while (skip_ansi &&
+		       (skip = display_mode_esc_sequence_len(string)) != 0)
+			string += skip;
 		width += utf8_width(&string, NULL);
 	}
+	return string ? width : len;
+}
+
+int utf8_strwidth(const char *string)
+{
+	return utf8_strnwidth(string, -1, 0);
 }
 
 int is_utf8(const char *text)

utf8.h

@@ -4,6 +4,7 @@
 typedef unsigned int ucs_char_t;  /* assuming 32bit int */
 
 int utf8_width(const char **start, size_t *remainder_p);
+int utf8_strnwidth(const char *string, int len, int skip_ansi);
 int utf8_strwidth(const char *string);
 int is_utf8(const char *text);
 int is_encoding_utf8(const char *name);