synthesize a traceback to get a normal exc_info from an exception

- as per https://docs.python.org/3.12/whatsnew/3.12.html#shutil, we must expect only an exception
  and *not* the full exc_info from the new onexc function (the documentation of this is very
  misleading and still uses the label "excinfo":
  https://docs.python.org/3.12/library/shutil.html#shutil.rmtree)

Author: cosmicexplorer

src/pip/_internal/utils/misc.py

@@ -1,5 +1,6 @@
 import contextlib
 import errno
+import functools
 import getpass
 import hashlib
 import io
@@ -14,7 +15,8 @@
 from functools import partial
 from io import StringIO
 from itertools import filterfalse, tee, zip_longest
-from types import TracebackType
+from pathlib import Path
+from types import FunctionType, TracebackType
 from typing import (
     Any,
     BinaryIO,
@@ -67,6 +69,8 @@
 ExcInfo = Tuple[Type[BaseException], BaseException, TracebackType]
 VersionInfo = Tuple[int, int, int]
 NetlocTuple = Tuple[str, Tuple[Optional[str], Optional[str]]]
+OnExc = Callable[[FunctionType, Path, BaseException], Any]
+OnErr = Callable[[FunctionType, Path, ExcInfo], Any]
 
 
 def get_pip_version() -> str:
@@ -121,22 +125,44 @@ def get_prog() -> str:
     return "pip"
 
 
+def bare_exc_to_onexc(exc_val: BaseException) -> ExcInfo:
+    exc_ty = type(exc_val)
+    tb = exc_val.__traceback__
+    if tb is None:
+        import inspect
+
+        frame = inspect.currentframe()
+        assert frame is not None
+        tb = TracebackType(None, frame, frame.f_lasti, frame.f_lineno)
+    return (exc_ty, exc_val, tb)
+
+
+def extract_exc_info_arg(f: OnErr) -> OnExc:
+    def g(fn: FunctionType, p: Path, e: BaseException) -> Any:
+        info = bare_exc_to_onexc(e)
+        return f(fn, p, info)
+
+    return functools.update_wrapper(g, f)
+
+
 # Retry every half second for up to 3 seconds
 # Tenacity raises RetryError by default, explicitly raise the original exception
 @retry(reraise=True, stop=stop_after_delay(3), wait=wait_fixed(0.5))
 def rmtree(
     dir: str,
     ignore_errors: bool = False,
-    onexc: Optional[Callable[[Any, Any, Any], Any]] = None,
+    onexc: Optional[OnErr] = None,
 ) -> None:
     if ignore_errors:
         onexc = _onerror_ignore
-    elif onexc is None:
+    if onexc is None:
         onexc = _onerror_reraise
+    handler: OnErr = partial(rmtree_errorhandler, onexc=onexc)
     if sys.version_info >= (3, 12):
-        shutil.rmtree(dir, onexc=partial(rmtree_errorhandler, onexc=onexc))
+        exc_handler = extract_exc_info_arg(handler)
+        shutil.rmtree(dir, onexc=exc_handler)
     else:
-        shutil.rmtree(dir, onerror=partial(rmtree_errorhandler, onexc=onexc))
+        shutil.rmtree(dir, onerror=handler)
 
 
 def _onerror_ignore(*_args: Any) -> None:

src/pip/_internal/utils/temp_dir.py

@@ -5,6 +5,7 @@
 import tempfile
 import traceback
 from contextlib import ExitStack, contextmanager
+from pathlib import Path
 from typing import (
     Any,
     Callable,
@@ -189,7 +190,7 @@ def cleanup(self) -> None:
 
         def onerror(
             func: Callable[[str], Any],
-            path: str,
+            path: Path,
             exc_info: Tuple[Type[BaseException], BaseException, Any],
         ) -> None:
             """Log a warning for a `rmtree` error and continue"""