Fix incorrect check for symlink in fake os.walk

- proposed by @giladreti
- fixes #559

CHANGES.md

@@ -12,6 +12,7 @@ The released versions correspond to PyPi releases.
   * add possibility to set file system OS via `FakeFilesystem.os` 
 
 #### Fixes
+  * fix check for link in `os.walk` (see [#559](../../issues/559))
   * fix handling of real files in combination with `home` if simulating
     Posix under Windows (see [#558](../../issues/558))
   * do not call fake `open` if called from skipped module  

pyfakefs/fake_scandir.py

@@ -241,12 +241,11 @@ def do_walk(top_dir, top_most=False):
                 yield top_contents
 
             for directory in top_contents[1]:
-                if not followlinks and filesystem.islink(directory):
+                path = filesystem.joinpaths(top_dir, directory)
+                if not followlinks and filesystem.islink(path):
                     continue
-                for contents in do_walk(filesystem.joinpaths(top_dir,
-                                                             directory)):
+                for contents in do_walk(path):
                     yield contents
-
             if not topdown:
                 yield top_contents
 

pyfakefs/tests/fake_os_test.py

@@ -4572,6 +4572,20 @@ def test_walk_followsymlink_enabled(self):
                                self.os.path.join(base_dir, 'created_link'),
                                followlinks=True)
 
+    def test_walk_linked_file_in_subdir(self):
+        # regression test for #559 (tested for link on incomplete path)
+        self.check_posix_only()
+        # need to have a top-level link to reproduce the bug - skip real fs
+        self.skip_real_fs()
+        file_path = '/foo/bar/baz'
+        self.create_file(file_path)
+        self.create_symlink('bar', file_path)
+        expected = [
+            ('/foo', ['bar'], []),
+            ('/foo/bar', [], ['baz'])
+        ]
+        self.assertWalkResults(expected, '/foo')
+
     def test_base_dirpath(self):
         # regression test for #512
         file_path = self.make_path('foo', 'bar', 'baz')