pretty: support truncating in %>, %< and %><

%>(N,trunc) truncates the right part after N columns and replace the
last two letters with "..". ltrunc does the same on the left. mtrunc
cuts the middle out.

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

utf8.c

@@ -421,6 +421,52 @@ void strbuf_add_wrapped_bytes(struct strbuf *buf, const char *data, int len,
 	free(tmp);
 }
 
+void strbuf_utf8_replace(struct strbuf *sb_src, int pos, int width,
+			 const char *subst)
+{
+	struct strbuf sb_dst = STRBUF_INIT;
+	char *src = sb_src->buf;
+	char *end = src + sb_src->len;
+	char *dst;
+	int w = 0, subst_len = 0;
+
+	if (subst)
+		subst_len = strlen(subst);
+	strbuf_grow(&sb_dst, sb_src->len + subst_len);
+	dst = sb_dst.buf;
+
+	while (src < end) {
+		char *old;
+		size_t n;
+
+		while ((n = display_mode_esc_sequence_len(src))) {
+			memcpy(dst, src, n);
+			src += n;
+			dst += n;
+		}
+
+		old = src;
+		n = utf8_width((const char**)&src, NULL);
+		if (!src) 	/* broken utf-8, do nothing */
+			return;
+		if (n && w >= pos && w < pos + width) {
+			if (subst) {
+				memcpy(dst, subst, subst_len);
+				dst += subst_len;
+				subst = NULL;
+			}
+			w += n;
+			continue;
+		}
+		memcpy(dst, old, src - old);
+		dst += src - old;
+		w += n;
+	}
+	strbuf_setlen(&sb_dst, dst - sb_dst.buf);
+	strbuf_attach(sb_src, strbuf_detach(&sb_dst, NULL),
+		      sb_dst.len, sb_dst.alloc);
+}
+
 int is_encoding_utf8(const char *name)
 {
 	if (!name)