Add test_imports (#77728)

That validates that every PyTorch submodule can be imported

Prevents regressions like the one described in https://github.com/pytorch/pytorch/issues/77441 from happening in the future

Pull Request resolved: https://github.com/pytorch/pytorch/pull/77728
Approved by: https://github.com/seemethere, https://github.com/janeyx99

test/test_testing.py

@@ -3,10 +3,13 @@
 import collections
 import doctest
 import functools
+import importlib
+import inspect
 import itertools
 import math
 import os
 import re
+import sys
 import unittest.mock
 from typing import Any, Callable, Iterator, List, Tuple
 
@@ -1762,5 +1765,43 @@ instantiate_parametrized_tests(TestTestParametrization)
 instantiate_device_type_tests(TestTestParametrizationDeviceType, globals())
 
 
+class TestImports(TestCase):
+    def test_circular_dependencies(self) -> None:
+        """ Checks that all modules inside torch can be imported
+        Prevents regression reported in https://github.com/pytorch/pytorch/issues/77441 """
+        ignored_modules = ["torch.utils.tensorboard",  # deps on tensorboard
+                           "torch.distributed.elastic.rendezvous",  # depps on etcd
+                           "torch.backends._coreml",  # depends on pycoreml
+                           "torch.contrib.",  # something weird
+                           "torch.testing._internal.common_fx2trt",  # needs fx
+                           "torch.testing._internal.distributed.",  # just fails
+                           ]
+        # See https://github.com/pytorch/pytorch/issues/77801
+        if not sys.version_info >= (3, 9):
+            ignored_modules.append("torch.utils.benchmark")
+        if IS_WINDOWS:
+            # Distributed does not work on Windows
+            ignored_modules.append("torch.distributed.")
+            ignored_modules.append("torch.testing._internal.dist_utils")
+
+        torch_dir = os.path.dirname(torch.__file__)
+        for base, folders, files in os.walk(torch_dir):
+            prefix = os.path.relpath(base, os.path.dirname(torch_dir)).replace(os.path.sep, ".")
+            for f in files:
+                if not f.endswith(".py"):
+                    continue
+                mod_name = f"{prefix}.{f[:-3]}" if f != "__init__.py" else prefix
+                # Do not attempt to import executable modules
+                if f == "__main__.py":
+                    continue
+                if any(mod_name.startswith(x) for x in ignored_modules):
+                    continue
+                try:
+                    mod = importlib.import_module(mod_name)
+                except Exception as e:
+                    raise RuntimeError(f"Failed to import {mod_name}: {e}") from e
+                self.assertTrue(inspect.ismodule(mod))
+
+
 if __name__ == '__main__':
     run_tests()