gh-109413: Add a custom script for running mypy on libregrtest

Lib/test/libregrtest/mypy.ini

@@ -31,3 +31,6 @@ strict_optional = False
 # Various internal modules that typeshed deliberately doesn't have stubs for:
 [mypy-_abc.*,_opcode.*,_overlapped.*,_testcapi.*,_testinternalcapi.*,test.*]
 ignore_missing_imports = True
+
+[mypy-test.support.*]
+disable_error_code = attr-defined,var-annotated,index,assignment

Lib/test/support/__init__.py

@@ -18,6 +18,7 @@
 import types
 import unittest
 import warnings
+from collections.abc import Callable
 
 from .testresult import get_test_runner
 
@@ -183,12 +184,12 @@ def get_attribute(obj, name):
     else:
         return attribute
 
-verbose = 1              # Flag set to 0 by regrtest.py
-use_resources = None     # Flag set to [] by regrtest.py
-max_memuse = 0           # Disable bigmem tests (they will still be run with
-                         # small sizes, to make sure they work.)
+verbose = 1                                     # Flag set to 0 by regrtest.py
+use_resources: tuple[str, ...] | None = None    # Flag set to a tuple by regrtest.py
+max_memuse = 0                                  # Disable bigmem tests (they will still be run with
+                                                # small sizes, to make sure they work.)
 real_max_memuse = 0
-junit_xml_list = None    # list of testsuite XML elements
+junit_xml_list: list | None = None              # list of testsuite XML elements
 failfast = False
 
 # _original_stdout is meant to hold stdout at the time regrtest began.
@@ -1325,6 +1326,18 @@ def flush_std_streams():
         sys.stderr.flush()
 
 
+class WarningsPrinter:
+    def __init__(self, func: Callable[[str], None]) -> None:
+        self.func = func
+        # bpo-39983: Store the original sys.stderr at Python startup to be able to
+        # log warnings even if sys.stderr is captured temporarily by a test.
+        self.orig_stderr = sys.stderr
+
+    def __call__(self, msg: str) -> None:
+        return self.func(msg)
+
+
+@WarningsPrinter
 def print_warning(msg):
     # bpo-45410: Explicitly flush stdout to keep logs in order
     flush_std_streams()
@@ -1333,10 +1346,6 @@ def print_warning(msg):
         print(f"Warning -- {line}", file=stream)
     stream.flush()
 
-# bpo-39983: Store the original sys.stderr at Python startup to be able to
-# log warnings even if sys.stderr is captured temporarily by a test.
-print_warning.orig_stderr = sys.stderr
-
 
 # Flag used by saved_test_environment of test.libregrtest.save_env,
 # to check if a test modified the environment. The flag should be set to False

Tools/scripts/run_mypy_on_regrtest.py

@@ -0,0 +1,58 @@
+"""
+Script to run mypy on Lib/test/libregrtest.
+
+This script is necessary due to the fact that,
+if you invoke mypy directly on anything inside the Lib/ directory,
+it (amusingly) thinks that everything in the stdlib is being "shadowed"
+by the modules inside `Lib/`.
+"""
+
+import argparse
+import os
+import shutil
+import subprocess
+import tempfile
+from pathlib import Path
+from typing import TypeAlias
+
+ReturnCode: TypeAlias = int
+
+
+def run_mypy_on_libregrtest(root_dir: Path) -> ReturnCode:
+    test_dot_support_dir = root_dir / "Lib/" / "test" / "support"
+    # Copy `Lib/test/support/` into a tempdir and point MYPYPATH towards the tempdir,
+    # so that mypy can see the classes and functions defined in `Lib/test/support/`
+    with tempfile.TemporaryDirectory() as td:
+        td_path = Path(td)
+        (td_path / "test").mkdir()
+        shutil.copytree(test_dot_support_dir, td_path / "test" / "support")
+        mypy_command = [
+            "mypy",
+            "--config-file",
+            "Lib/test/libregrtest/mypy.ini",
+        ]
+        result = subprocess.run(
+            mypy_command, cwd=root_dir, env=os.environ | {"MYPYPATH": td}
+        )
+        return result.returncode
+
+
+def main() -> ReturnCode:
+    parser = argparse.ArgumentParser("Script to run mypy on Lib/test/regrtest/")
+    parser.add_argument(
+        "--root-dir",
+        "-r",
+        type=Path,
+        required=True,
+        help="path to the CPython repo root",
+    )
+    args = parser.parse_args()
+    root_dir = args.root_dir
+    test_dot_support_dir = root_dir / "Lib" / "test" / "support"
+    if not (test_dot_support_dir.exists() and test_dot_support_dir.is_dir()):
+        parser.error("--root-dir must point to the root of a CPython clone!")
+    return run_mypy_on_libregrtest(root_dir)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())