Fix the stubgen test flake.

mypy/stubgen.py

@@ -153,13 +153,6 @@ def find_module_path_and_all(module: str, pyversion: Tuple[int, int],
             try:
                 mod = importlib.import_module(module)
             except Exception:
-                # Print some debugging output that might help diagnose problems.
-                print('=== debug dump follows ===')
-                traceback.print_exc()
-                dump_sys_path()
-                print('PYTHONPATH: %s' % os.getenv("PYTHONPATH"))
-                dump_dir(os.getcwd())
-                print('=== end of debug dump ===')
                 raise CantImport(module)
             if is_c_module(mod):
                 return None
@@ -175,31 +168,6 @@ def find_module_path_and_all(module: str, pyversion: Tuple[int, int],
     return module_path, module_all
 
 
-def dump_sys_path() -> None:
-    print('sys.path:')
-    for entry in sys.path:
-        print('    %r' % entry)
-        if entry in sys.path_importer_cache:
-            x = sys.path_importer_cache[entry]
-            print('      path_importer: %r / %r' % (x, getattr(x, '__dict__', None)))
-            try:
-                print('      stat: %s ' % str(os.stat(entry)))
-            except Exception as e:
-                pass
-
-
-def dump_dir(path: str) -> None:
-    for root, dirs, files in os.walk(os.getcwd()):
-        print('%s:' % root)
-        for d in dirs:
-            print('    %s/' % d)
-        for f in files:
-            path = os.path.join(root, f)
-            print('    %s (%d bytes)' % (f, os.path.getsize(path)))
-        if not dirs and not files:
-            print('    (empty)')
-
-
 def load_python_module_info(module: str, interpreter: str) -> Tuple[str, Optional[List[str]]]:
     """Return tuple (module path, module __all__) for a Python 2 module.
 

mypy/test/teststubgen.py

@@ -1,5 +1,4 @@
 import glob
-import importlib
 import os.path
 import shutil
 import sys
@@ -125,7 +124,7 @@ def test_stubgen(testcase: DataDrivenTestCase) -> None:
         handle.close()
         # Without this we may sometimes be unable to import the module below, as importlib
         # caches os.listdir() results in Python 3.3+ (Guido explained this to me).
-        reset_importlib_caches()
+        reset_importlib_cache('stubgen-test-path')
         try:
             if testcase.name.endswith('_import'):
                 generate_stub_for_module(name, out_dir, quiet=True,
@@ -145,11 +144,16 @@ def test_stubgen(testcase: DataDrivenTestCase) -> None:
         shutil.rmtree(out_dir)
 
 
-def reset_importlib_caches() -> None:
-    try:
-        importlib.invalidate_caches()
-    except (ImportError, AttributeError):
-        pass
+def reset_importlib_cache(entry: str) -> None:
+    # importlib.invalidate_caches() is insufficient, since it doesn't
+    # clear cache entries that indicate that a directory on the path
+    # does not exist, which can cause failures.  Just directly clear
+    # the sys.path_importer_cache entry ourselves.  Other possible
+    # workarounds include always using different paths in the sys.path
+    # (perhaps by using the full path name) or removing the entry from
+    # sys.path after each run.
+    if entry in sys.path_importer_cache:
+        del sys.path_importer_cache[entry]
 
 
 def load_output(dirname: str) -> List[str]: