#11731: simplify/enhance parser/generator API by introducing policy objects.

This new interface will also allow for future planned enhancements
in control over the parser/generator without requiring any additional
complexity in the parser/generator API.

Patch reviewed by Éric Araujo and Barry Warsaw.

Lib/test/test_email/test_generator.py

@@ -0,0 +1,136 @@
+import io
+import textwrap
+import unittest
+from email import message_from_string, message_from_bytes
+from email.generator import Generator, BytesGenerator
+from email import policy
+from test.test_email import TestEmailBase
+
+# XXX: move generator tests from test_email into here at some point.
+
+
+class TestGeneratorBase():
+
+    long_subject = {
+        0: textwrap.dedent("""\
+            To: whom_it_may_concern@example.com
+            From: nobody_you_want_to_know@example.com
+            Subject: We the willing led by the unknowing are doing the
+             impossible for the ungrateful. We have done so much for so long with so little
+             we are now qualified to do anything with nothing.
+
+            None
+            """),
+        40: textwrap.dedent("""\
+            To: whom_it_may_concern@example.com
+            From:\x20
+             nobody_you_want_to_know@example.com
+            Subject: We the willing led by the
+             unknowing are doing the
+             impossible for the ungrateful. We have
+             done so much for so long with so little
+             we are now qualified to do anything
+             with nothing.
+
+            None
+            """),
+        20: textwrap.dedent("""\
+            To:\x20
+             whom_it_may_concern@example.com
+            From:\x20
+             nobody_you_want_to_know@example.com
+            Subject: We the
+             willing led by the
+             unknowing are doing
+             the
+             impossible for the
+             ungrateful. We have
+             done so much for so
+             long with so little
+             we are now
+             qualified to do
+             anything with
+             nothing.
+
+            None
+            """),
+        }
+    long_subject[100] = long_subject[0]
+
+    def maxheaderlen_parameter_test(self, n):
+        msg = self.msgmaker(self.long_subject[0])
+        s = self.ioclass()
+        g = self.genclass(s, maxheaderlen=n)
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), self.long_subject[n])
+
+    def test_maxheaderlen_parameter_0(self):
+        self.maxheaderlen_parameter_test(0)
+
+    def test_maxheaderlen_parameter_100(self):
+        self.maxheaderlen_parameter_test(100)
+
+    def test_maxheaderlen_parameter_40(self):
+        self.maxheaderlen_parameter_test(40)
+
+    def test_maxheaderlen_parameter_20(self):
+        self.maxheaderlen_parameter_test(20)
+
+    def maxheaderlen_policy_test(self, n):
+        msg = self.msgmaker(self.long_subject[0])
+        s = self.ioclass()
+        g = self.genclass(s, policy=policy.default.clone(max_line_length=n))
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), self.long_subject[n])
+
+    def test_maxheaderlen_policy_0(self):
+        self.maxheaderlen_policy_test(0)
+
+    def test_maxheaderlen_policy_100(self):
+        self.maxheaderlen_policy_test(100)
+
+    def test_maxheaderlen_policy_40(self):
+        self.maxheaderlen_policy_test(40)
+
+    def test_maxheaderlen_policy_20(self):
+        self.maxheaderlen_policy_test(20)
+
+    def maxheaderlen_parm_overrides_policy_test(self, n):
+        msg = self.msgmaker(self.long_subject[0])
+        s = self.ioclass()
+        g = self.genclass(s, maxheaderlen=n,
+                          policy=policy.default.clone(max_line_length=10))
+        g.flatten(msg)
+        self.assertEqual(s.getvalue(), self.long_subject[n])
+
+    def test_maxheaderlen_parm_overrides_policy_0(self):
+        self.maxheaderlen_parm_overrides_policy_test(0)
+
+    def test_maxheaderlen_parm_overrides_policy_100(self):
+        self.maxheaderlen_parm_overrides_policy_test(100)
+
+    def test_maxheaderlen_parm_overrides_policy_40(self):
+        self.maxheaderlen_parm_overrides_policy_test(40)
+
+    def test_maxheaderlen_parm_overrides_policy_20(self):
+        self.maxheaderlen_parm_overrides_policy_test(20)
+
+
+class TestGenerator(TestGeneratorBase, TestEmailBase):
+
+    msgmaker = staticmethod(message_from_string)
+    genclass = Generator
+    ioclass = io.StringIO
+
+
+class TestBytesGenerator(TestGeneratorBase, TestEmailBase):
+
+    msgmaker = staticmethod(message_from_bytes)
+    genclass = BytesGenerator
+    ioclass = io.BytesIO
+    long_subject = {key: x.encode('ascii')
+        for key, x in TestGeneratorBase.long_subject.items()}
+
+
+if __name__ == '__main__':
+    unittest.main()