1 files changed, 55 insertions, 0 deletions
diff --git a/src/path.c b/src/path.c
index 77f8d8858..d29b992fe 100644
--- a/src/path.c
+++ b/src/path.c
@@ -750,6 +750,61 @@ int git_path_cmp(
 	return (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
 }
 
+int git_path_make_relative(git_buf *path, const char *parent)
+{
+	const char *p, *q, *p_dirsep, *q_dirsep;
+	size_t plen = path->size, newlen, depth = 1, i;
+
+	for (p_dirsep = p = path->ptr, q_dirsep = q = parent; *p && *q; p++, q++) {
+		if (*p == '/' && *q == '/') {
+			p_dirsep = p;
+			q_dirsep = q;
+		}
+		else if (*p != *q)
+			break;
+	}
+
+	/* need at least 1 common path segment */
+	if ((p_dirsep == path->ptr || q_dirsep == parent) &&
+		(*p_dirsep != '/' || *q_dirsep != '/')) {
+		giterr_set(GITERR_INVALID,
+			"%s is not a parent of %s", parent, path->ptr);
+		return GIT_ENOTFOUND;
+	}
+
+	if (*p == '/' && !*q)
+		p++;
+	else if (!*p && *q == '/')
+		q++;
+	else if (!*p && !*q)
+		return git_buf_clear(path), 0;
+	else {
+		p = p_dirsep + 1;
+		q = q_dirsep + 1;
+	}
+
+	plen -= (p - path->ptr);
+
+	if (!*q)
+		return git_buf_set(path, p, plen);
+
+	for (; (q = strchr(q, '/')) && *(q + 1); q++)
+		depth++;
+
+	newlen = (depth * 3) + plen;
+
+	if (git_buf_try_grow(path, newlen + 1, 1, 0) < 0)
+		return -1;
+
+	memmove(path->ptr + (depth * 3), p, plen + 1);
+
+	for (i = 0; i < depth; i++)
+		memcpy(path->ptr + (i * 3), "../", 3);
+
+	path->size = newlen;
+	return 0;
+}
+
 bool git_path_has_non_ascii(const char *path, size_t pathlen)
 {
 	const uint8_t *scan = (const uint8_t *)path, *end;