bug: fix use of skip_current_dir

The method sometimes destroyed an internal invariant by not decreasing
`oldest_opened`. That then leads to panics in `push`. We fix this by
calling the canonical `pop` function, which is what should have happened
from the beginning.

This includes a regression test that fails without this fix.

Fixes #118, Closes #124

src/lib.rs

@@ -724,10 +724,7 @@ impl IntoIter {
     /// [`filter_entry`]: #method.filter_entry
     pub fn skip_current_dir(&mut self) {
         if !self.stack_list.is_empty() {
-            self.stack_list.pop();
+            self.pop();
-        }
-        if !self.stack_path.is_empty() {
-            self.stack_path.pop();
         }
     }
 

src/tests/recursive.rs

@@ -990,3 +990,23 @@ fn same_file_system() {
     ];
     assert_eq!(expected, r.sorted_paths());
 }
+
+// Tests that skip_current_dir doesn't destroy internal invariants.
+//
+// See: https://github.com/BurntSushi/walkdir/issues/118
+#[test]
+fn regression_skip_current_dir() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/a/b");
+    dir.mkdirp("foo/1/2");
+
+    let mut wd = WalkDir::new(dir.path()).max_open(1).into_iter();
+    wd.next();
+    wd.next();
+    wd.next();
+    wd.next();
+
+    wd.skip_current_dir();
+    wd.skip_current_dir();
+    wd.next();
+}