Make sure that __dir__ returns a new copy of __all__

__dir__ should probably return new copies for each call so that the
result will stay the same regardless of how the result of previous calls
was modified.

Author: lagru

lazy_loader/__init__.py

@@ -90,7 +90,7 @@ def __getattr__(name):
             raise AttributeError(f"No {package_name} attribute {name}")
 
     def __dir__():
-        return __all__
+        return list(__all__)
 
     if os.environ.get("EAGER_IMPORT", ""):
         for attr in set(attr_to_modules.keys()) | submodules:

lazy_loader/tests/test_lazy_loader.py

@@ -104,6 +104,29 @@ def test_lazy_attach():
             assert locls[k] == v
 
 
+def test_lazy_attach_returns_copies():
+    _get, _dir, _all = lazy.attach(
+        __name__, ["my_submodule", "another_submodule"], {"foo": ["some_attr"]}
+    )
+    assert _dir() is not _dir()
+    assert _dir() == _all
+    assert _dir() is not _all
+
+    expected = ["another_submodule", "my_submodule", "some_attr"]
+    assert _dir() == expected
+    assert _all == expected
+    assert _dir() is not _all
+
+    _dir().append("modify_returned_list")
+    assert _dir() == expected
+    assert _all == expected
+    assert _dir() is not _all
+
+    _all.append("modify_returned_all")
+    assert _dir() == expected
+    assert _all == expected + ["modify_returned_all"]
+
+
 def test_attach_same_module_and_attr_name():
     from lazy_loader.tests import fake_pkg