ftw: Include sub-directories in the result of `scandir'.

* module/ice-9/ftw.scm (scandir)[skip]: Keep NAME in the resulting list.

* test-suite/tests/ftw.test ("scandir")["top-srcdir"]: New test.

module/ice-9/ftw.scm

@@ -530,7 +530,7 @@ of file names is sorted according to ENTRY<?, which defaults to
 
   (define (skip name stat result)
     ;; All the sub-directories are skipped.
-    result)
+    (cons (basename name) result))
 
   (and=> (file-system-fold enter? leaf down up skip #f name stat)
          (lambda (files)

test-suite/tests/ftw.test

@@ -169,6 +169,18 @@
 
 (with-test-prefix "scandir"
 
+  (pass-if "top-srcdir"
+    (let ((valid? (negate (cut string-any #\/ <>))))
+      (match (scandir %top-srcdir)
+        (((? valid? files) ...)
+         ;; Both subdirs and files must be included.
+         (let ((expected '("libguile" "README" "COPYING"
+                           "test-suite" "Makefile.am"
+                           "." "..")))
+           (lset= string=?
+                  (lset-intersection string=? files expected)
+                  expected))))))
+
   (pass-if "test-suite"
     (let ((select? (cut string-suffix? ".test" <>)))
       (match (scandir (string-append %test-dir "/tests") select?)