vfs: fix virtual entries leak in removed directory

Deleting the contents of a directory and then the directory itself,
before a listing has confirmed the deletes, left the directory's
virtual entries behind. They are counted in every parent directory, and
a directory which counts virtual entries refuses to forget its cache, so
vfs/forget could not make changes made outside rclone visible.

This lasted until the removed directory's own cleanup timer purged its
entries, which happens 2 x --dir-cache-time later.

This fix drops the removed directory's virtual entries once it has been
removed.

Fixes #10083

vfs/dir.go

@@ -1142,6 +1142,15 @@ func (d *Dir) Remove() error {
 		fs.Errorf(d, "Dir.Remove failed to remove directory: %v", err)
 		return err
 	}
+	// The directory is gone, so no listing will resolve its virtual
+	// entries, which can only be deletes as it was empty. They must be
+	// removed now, or they will be counted in every parent and
+	// cache forgets blocked as a consequence
+	d.mu.Lock()
+	for leaf := range d.virtual {
+		d._deleteVirtual(leaf)
+	}
+	d.mu.Unlock()
 	// Remove the item from the parent directory listing
 	if d.parent != nil {
 		d.parent.delObject(d.Name())

vfs/dir_test.go

@@ -553,6 +553,24 @@ func TestDirRemove(t *testing.T) {
 	assert.Equal(t, EROFS, err)
 }
 
+// Removing a directory leaves no virtual entries counted in its parent, so the
+// parent can still forget its cache.
+func TestDirRemoveVirtuals(t *testing.T) {
+	_, vfs, dir, _ := dirCreate(t)
+	root, err := vfs.Root()
+	require.NoError(t, err)
+
+	// Remove the directory's contents and then the directory, before a
+	// listing has confirmed the contents are gone.
+	require.NoError(t, dir.RemoveName("file1"))
+	require.NoError(t, root.RemoveName("dir"))
+
+	assert.False(t, root.ForgetAll(), "root holds virtual entries after rmdir")
+
+	dir.ForgetAll()
+	assert.False(t, root.ForgetAll(), "root holds virtual entries after the removed dir is forgotten")
+}
+
 func TestDirRemoveAll(t *testing.T) {
 	r, vfs, dir, _ := dirCreate(t)