bpo-33116: Add 'Field' to dataclasses.__all__. (GH-6182) (GH-6183)

- Add missing 'Field' to __all__.
- Improve tests to catch this.
(cherry picked from commit 8e4560a9da)

Co-authored-by: Eric V. Smith <ericvsmith@users.noreply.github.com>

Lib/dataclasses.py

@@ -5,6 +5,7 @@ import inspect
 
 __all__ = ['dataclass',
            'field',
+           'Field',
            'FrozenInstanceError',
            'InitVar',
            'MISSING',
@@ -513,7 +514,7 @@ def _get_field(cls, a_name, a_type):
     #  and InitVars are also returned, but marked as such (see
     #  f._field_type).
 
-    # If the default value isn't derived from field, then it's
+    # If the default value isn't derived from Field, then it's
     #  only a normal default value.  Convert it to a Field().
     default = getattr(cls, a_name, MISSING)
     if isinstance(default, Field):

Lib/test/test_dataclasses.py

@@ -1,7 +1,8 @@
-from dataclasses import (
-    dataclass, field, FrozenInstanceError, fields, asdict, astuple,
-    make_dataclass, replace, InitVar, Field, MISSING, is_dataclass,
-)
+# Deliberately use "from dataclasses import *".  Every name in __all__
+# is tested, so they all must be present.  This is a way to catch
+# missing ones.
+
+from dataclasses import *
 
 import pickle
 import inspect

Misc/NEWS.d/next/Library/2018-03-21-16-52-26.bpo-33116.Tvzerj.rst

@@ -0,0 +1 @@
+Add 'Field' to dataclasses.__all__.