dirtree->name is an array, not a pointer, so can't be zero. Remove the test.
We dereference plen without checking it for null but calling dirtree_path(0, 0)
is pilot error: only the _first_ call can have plen = 0. Add a comment.
// Return path to this node, assembled recursively.
+// Initial call can pass in NULL to plen, or point to an int initialized to 0
+// to return the length of the path, or a value greater than 0 to allocate
+// extra space if you want to append your own text to the string.
+
char *dirtree_path(struct dirtree *node, int *plen)
{
char *path;
int len;
- if (!node || !node->name) {
+ if (!node) {
path = xmalloc(*plen);
*plen = 0;
return path;