Ensure builtin modules are from typeshed sooner

It should work now with custom-typeshed-dir.

Fixes python#1876

mypy/build.py

@@ -605,6 +605,31 @@ def __init__(self, data_dir: str,
  self.fscache = fscache
  self.find_module_cache = FindModuleCache(self.search_paths, self.fscache, self.options,
  source_set=self.source_set)
+ for module in CORE_BUILTIN_MODULES:
+ if options.use_builtins_fixtures:
+ continue
+ if module == "_importlib_modulespec":
+ continue
+ path = self.find_module_cache.find_module(module)
+ if not isinstance(path, str):
+ raise CompileError([
+ f"Failed to find builtin module {module}, perhaps typeshed is broken?",
+ ])
+ if is_typeshed_file(path):
+ continue
+ if is_stub_package_file(path):
+ continue
+ if options.custom_typeshed_dir is not None:
+ # Check if module lives under custom_typeshed_dir subtree
+ custom_typeshed_dir = os.path.abspath(options.custom_typeshed_dir)
+ if os.path.commonpath((path, custom_typeshed_dir)) == custom_typeshed_dir:
+ continue
+
+ raise CompileError([
+ f'mypy: "{os.path.relpath(path)}" shadows library module "{module}"',
+ f'note: A user-defined top-level module with name "{module}" is not supported'
+ ])
+
  self.metastore = create_metastore(options)
 
  # a mapping from source files to their corresponding shadow files
@@ -2459,15 +2484,6 @@ def find_module_and_diagnose(manager: BuildManager,
  if is_sub_path(result, dir):
  # Silence errors in site-package dirs and typeshed
  follow_imports = 'silent'
- if (id in CORE_BUILTIN_MODULES
- and not is_typeshed_file(result)
- and not is_stub_package_file(result)
- and not options.use_builtins_fixtures
- and not options.custom_typeshed_dir):
- raise CompileError([
- f'mypy: "{os.path.relpath(result)}" shadows library module "{id}"',
- f'note: A user-defined top-level module with name "{id}" is not supported'
- ])
  return (result, follow_imports)
  else:
  # Could not find a module. Typically the reason is a

mypy/test/testgraph.py

@@ -38,6 +38,7 @@ def test_scc(self) -> None:
  def _make_manager(self) -> BuildManager:
  errors = Errors()
  options = Options()
+ options.use_builtins_fixtures = True
  fscache = FileSystemCache()
  search_paths = SearchPaths((), (), (), ())
  manager = BuildManager(

mypy/util.py

@@ -51,6 +51,8 @@
  "__init__", "__new__", "__call__", "__init_subclass__", "__class_getitem__",
 ))
 
+TYPESHED_DIR: Final = os.path.join(os.path.dirname(__file__), 'typeshed')
+
 
 def is_dunder(name: str, exclude_special: bool = False) -> bool:
  """Returns whether name is a dunder name.
@@ -745,16 +747,15 @@ def format_error(
 
 
 def is_typeshed_file(file: str) -> bool:
- # gross, but no other clear way to tell
- return 'typeshed' in os.path.abspath(file).split(os.sep)
+ return os.path.commonpath((TYPESHED_DIR, os.path.abspath(file))) == TYPESHED_DIR
 
 
 def is_stub_package_file(file: str) -> bool:
  # Use hacky heuristics to check whether file is part of a PEP 561 stub package.
  if not file.endswith('.pyi'):
  return False
  return any(component.endswith('-stubs')
- for component in os.path.abspath(file).split(os.sep))
+ for component in os.path.split(os.path.abspath(file)))
 
 
 def unnamed_function(name: Optional[str]) -> bool:

test-data/unit/cmdline.test

@@ -1425,3 +1425,22 @@ b\.c \d+
 # cmd: mypy --enable-incomplete-features a.py
 [file a.py]
 pass
+
+[case testShadowTypingModuleEarlyLoad]
+# cmd: mypy .
+from typing import Union
+
+def foo(a: Union[int, str]) -> str:
+ return str
+[file typing.py]
+import sys
+import os
+del sys.modules["typing"]
+path = sys.path
+sys.path.remove(os.getcwd())
+from typing import *
+sys.path = path
+[out]
+mypy: "tmp/typing.py" shadows library module "typing"
+note: A user-defined top-level module with name "typing" is not supported
+== Return code: 2