bpo-35753: Fix crash in doctest with unwrap-able functions (GH-22981) (#25926)

Ignore objects that inspect.unwrap throws due to
too many wrappers.  This is a very rare case, however
it can easily be surfaced when a module under doctest
imports unitest.mock.call into its namespace.

We simply skip any object that throws this exception.
This should handle the majority of cases.
(cherry picked from commit 565a31804c)

Co-authored-by: Alfred Perlstein <alfred@fb.com>

Lib/test/test_doctest.py

@@ -15,6 +15,7 @@
 import unittest
 import tempfile
 import shutil
+import types
 import contextlib
 
 # NOTE: There are some additional tests relating to interaction with
@@ -443,7 +444,7 @@ def basics(): r"""
     >>> tests = finder.find(sample_func)
 
     >>> print(tests)  # doctest: +ELLIPSIS
-    [<DocTest sample_func from ...:27 (1 example)>]
+    [<DocTest sample_func from test_doctest.py:28 (1 example)>]
 
 The exact name depends on how test_doctest was invoked, so allow for
 leading path components.
@@ -698,6 +699,18 @@ def non_Python_modules(): r"""
 
 class TestDocTestFinder(unittest.TestCase):
 
+    def test_issue35753(self):
+        # This import of `call` should trigger issue35753 when
+        # `support.run_doctest` is called due to unwrap failing,
+        # however with a patched doctest this should succeed.
+        from unittest.mock import call
+        dummy_module = types.ModuleType("dummy")
+        dummy_module.__dict__['inject_call'] = call
+        try:
+            support.run_doctest(dummy_module, verbosity=True)
+        except ValueError as e:
+            raise support.TestFailed("Doctest unwrap failed") from e
+
     def test_empty_namespace_package(self):
         pkg_name = 'doctest_empty_pkg'
         with tempfile.TemporaryDirectory() as parent_dir: