bpo-32505: dataclasses: raise TypeError if a member variable is of type Field, but doesn't have a type annotation. (GH-6192)

If a dataclass has a member variable that's of type Field, but it doesn't have a type annotation, raise TypeError.
(cherry picked from commit 56970b8ce9)

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

Lib/test/test_dataclasses.py

@@ -24,6 +24,14 @@ class TestCase(unittest.TestCase):
         o = C()
         self.assertEqual(len(fields(C)), 0)
 
+    def test_no_fields_but_member_variable(self):
+        @dataclass
+        class C:
+            i = 0
+
+        o = C()
+        self.assertEqual(len(fields(C)), 0)
+
     def test_one_field_no_default(self):
         @dataclass
         class C:
@@ -1906,6 +1914,41 @@ class TestCase(unittest.TestCase):
                                              'z': 'typing.Any'})
 
 
+class TestFieldNoAnnotation(unittest.TestCase):
+    def test_field_without_annotation(self):
+        with self.assertRaisesRegex(TypeError,
+                                    "'f' is a field but has no type annotation"):
+            @dataclass
+            class C:
+                f = field()
+
+    def test_field_without_annotation_but_annotation_in_base(self):
+        @dataclass
+        class B:
+            f: int
+
+        with self.assertRaisesRegex(TypeError,
+                                    "'f' is a field but has no type annotation"):
+            # This is still an error: make sure we don't pick up the
+            # type annotation in the base class.
+            @dataclass
+            class C(B):
+                f = field()
+
+    def test_field_without_annotation_but_annotation_in_base_not_dataclass(self):
+        # Same test, but with the base class not a dataclass.
+        class B:
+            f: int
+
+        with self.assertRaisesRegex(TypeError,
+                                    "'f' is a field but has no type annotation"):
+            # This is still an error: make sure we don't pick up the
+            # type annotation in the base class.
+            @dataclass
+            class C(B):
+                f = field()
+
+
 class TestDocString(unittest.TestCase):
     def assertDocStrEqual(self, a, b):
         # Because 3.6 and 3.7 differ in how inspect.signature work