bpo-45324: Capture data in FrozenImporter.find_spec() to use in exec_module(). (gh-28633)

Before this change we end up duplicating effort and throwing away data in FrozenImporter.find_spec().  Now we do the work once in find_spec() and the only thing we do in FrozenImporter.exec_module() is turn the raw frozen data into a code object and then exec it.

We've added _imp.find_frozen(), add an arg to _imp.get_frozen_object(), and updated FrozenImporter.  We've also moved some code around to reduce duplication, get a little more consistency in outcomes, and be more efficient.

Note that this change is mostly necessary if we want to set __file__ on frozen stdlib modules. (See https://bugs.python.org/issue21736.)

https://bugs.python.org/issue45324

Lib/test/test_importlib/frozen/test_loader.py

@@ -4,7 +4,9 @@ from .. import util
 machinery = util.import_importlib('importlib.machinery')
 
 from test.support import captured_stdout, import_helper
+import _imp
 import contextlib
+import marshal
 import types
 import unittest
 import warnings
@@ -33,11 +35,14 @@ class ExecModuleTests(abc.LoaderTests):
     def exec_module(self, name):
         with import_helper.frozen_modules():
             is_package = self.machinery.FrozenImporter.is_package(name)
+            code = _imp.get_frozen_object(name)
+        data = marshal.dumps(code)
         spec = self.machinery.ModuleSpec(
             name,
             self.machinery.FrozenImporter,
             origin='frozen',
             is_package=is_package,
+            loader_state=data,
         )
         module = types.ModuleType(name)
         module.__spec__ = spec
@@ -61,6 +66,7 @@ class ExecModuleTests(abc.LoaderTests):
             self.assertEqual(getattr(module, attr), value)
         self.assertEqual(output, 'Hello world!\n')
         self.assertTrue(hasattr(module, '__spec__'))
+        self.assertIsNone(module.__spec__.loader_state)
 
     def test_package(self):
         name = '__phello__'
@@ -73,6 +79,7 @@ class ExecModuleTests(abc.LoaderTests):
                                  name=name, attr=attr, given=attr_value,
                                  expected=value))
         self.assertEqual(output, 'Hello world!\n')
+        self.assertIsNone(module.__spec__.loader_state)
 
     def test_lacking_parent(self):
         name = '__phello__.spam'