gh-125063: marshal: Add version 5, improve documentation (GH-126829)

* Document that slices can be marshalled
* Deduplicate and organize the list of supported types
  in docs
* Organize the type code list in marshal.c, to make
  it more obvious that this is a versioned format
* Back-fill some historical info

Co-authored-by: Michael Droettboom <mdboom@gmail.com>

Lib/test/test_marshal.py

@@ -28,6 +28,13 @@ class HelperMixin:
         finally:
             os_helper.unlink(os_helper.TESTFN)
 
+def omit_last_byte(data):
+    """return data[:-1]"""
+    # This file's code is used in CompatibilityTestCase,
+    # but slices need marshal version 5.
+    # Avoid the slice literal.
+    return data[slice(0, -1)]
+
 class IntTestCase(unittest.TestCase, HelperMixin):
     def test_ints(self):
         # Test a range of Python ints larger than the machine word size.
@@ -241,7 +248,8 @@ class BugsTestCase(unittest.TestCase):
     def test_patch_873224(self):
         self.assertRaises(Exception, marshal.loads, b'0')
         self.assertRaises(Exception, marshal.loads, b'f')
-        self.assertRaises(Exception, marshal.loads, marshal.dumps(2**65)[:-1])
+        self.assertRaises(Exception, marshal.loads,
+                          omit_last_byte(marshal.dumps(2**65)))
 
     def test_version_argument(self):
         # Python 2.4.0 crashes for any call to marshal.dumps(x, y)
@@ -594,6 +602,19 @@ class InterningTestCase(unittest.TestCase, HelperMixin):
         s2 = sys.intern(s)
         self.assertNotEqual(id(s2), id(s))
 
+class SliceTestCase(unittest.TestCase, HelperMixin):
+    def test_slice(self):
+        for obj in (
+            slice(None), slice(1), slice(1, 2), slice(1, 2, 3),
+            slice({'set'}, ('tuple', {'with': 'dict'}, ), self.helper.__code__)
+        ):
+            with self.subTest(obj=str(obj)):
+                self.helper(obj)
+
+                for version in range(4):
+                    with self.assertRaises(ValueError):
+                        marshal.dumps(obj, version)
+
 @support.cpython_only
 @unittest.skipUnless(_testcapi, 'requires _testcapi')
 class CAPI_TestCase(unittest.TestCase, HelperMixin):
@@ -654,7 +675,7 @@ class CAPI_TestCase(unittest.TestCase, HelperMixin):
             self.assertEqual(r, obj)
 
             with open(os_helper.TESTFN, 'wb') as f:
-                f.write(data[:1])
+                f.write(omit_last_byte(data))
             with self.assertRaises(EOFError):
                 _testcapi.pymarshal_read_last_object_from_file(os_helper.TESTFN)
             os_helper.unlink(os_helper.TESTFN)
@@ -671,7 +692,7 @@ class CAPI_TestCase(unittest.TestCase, HelperMixin):
             self.assertEqual(p, len(data))
 
             with open(os_helper.TESTFN, 'wb') as f:
-                f.write(data[:1])
+                f.write(omit_last_byte(data))
             with self.assertRaises(EOFError):
                 _testcapi.pymarshal_read_object_from_file(os_helper.TESTFN)
             os_helper.unlink(os_helper.TESTFN)