Add script that prints compiled files when self compiling (#19260)

Patch various things and run setup.py to get compilation targets without
compiling anything. This can be useful for setting up a custom way of
compiling mypy/mypyc.

Author: JukkaL

misc/self_compile_info.py

@@ -0,0 +1,45 @@
+"""Print list of files compiled when compiling self (mypy and mypyc)."""
+
+import argparse
+import sys
+from typing import Any
+
+import setuptools
+
+import mypyc.build
+
+
+class FakeExtension:
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        pass
+
+
+def fake_mypycify(args: list[str], **kwargs: Any) -> list[FakeExtension]:
+    for target in sorted(args):
+        if not target.startswith("-"):
+            print(target)
+    return [FakeExtension()]
+
+
+def fake_setup(*args: Any, **kwargs: Any) -> Any:
+    pass
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(
+        description="Print list of files compiled when compiling self. Run in repository root."
+    )
+    parser.parse_args()
+
+    # Prepare fake state for running setup.py.
+    mypyc.build.mypycify = fake_mypycify  # type: ignore[assignment]
+    setuptools.Extension = FakeExtension  # type: ignore[misc, assignment]
+    setuptools.setup = fake_setup
+    sys.argv = [sys.argv[0], "--use-mypyc"]
+
+    # Run setup.py at the root of the repository.
+    import setup  # noqa: F401
+
+
+if __name__ == "__main__":
+    main()