Pull thread-local into _compat module to fix cloudpickling.

Because cloudpickle tries to pickle a function's globals, when it
pickled an attrs instance, it would try to pickle the `__repr__` method
and its globals, which included a `threading.local`. This broke
cloudpickle for all attrs classes unless they explicitly specified
`repr=False`. Modules, however, are pickled by reference, not by value,
so moving the repr into a different module means we can put `_compat`
into the function's globals and not worry about direct references.

src/attr/_compat.py

@@ -2,6 +2,7 @@
 
 import platform
 import sys
+import threading
 import types
 import warnings
 
@@ -243,3 +244,17 @@ def func():
 
 
 set_closure_cell = make_set_closure_cell()
+
+# Thread-local global to track attrs instances which are already being repr'd.
+# This is needed because there is no other (thread-safe) way to pass info
+# about the instances that are already being repr'd through the call stack
+# in order to ensure we don't perform infinite recursion.
+#
+# For instance, if an instance contains a dict which contains that instance,
+# we need to know that we're already repr'ing the outside instance from within
+# the dict's repr() call.
+#
+# This lives here rather than in _make.py so that the functions in _make.py
+# don't have a direct reference to the thread-local in their globals dict.
+# If they have such a reference, it breaks cloudpickle.
+repr_context = threading.local()

src/attr/_make.py

@@ -4,24 +4,11 @@
 import inspect
 import linecache
 import sys
-import threading
 import warnings
 
 from operator import itemgetter
 
-from . import _config, setters
-from ._compat import (
- HAS_F_STRINGS,
- PY2,
- PY310,
- PYPY,
- isclass,
- iteritems,
- metadata_proxy,
- new_class,
- ordered_dict,
- set_closure_cell,
-)
+from . import _compat, _config, setters
 from .exceptions import (
  DefaultAlreadySetError,
  FrozenInstanceError,
@@ -31,7 +18,7 @@
 )
 
 
-if not PY2:
+if not _compat.PY2:
  import typing
 
 
@@ -53,7 +40,7 @@
 # (when slots=True)
 _hash_cache_field = "_attrs_cached_hash"
 
-_empty_metadata_singleton = metadata_proxy({})
+_empty_metadata_singleton = _compat.metadata_proxy({})
 
 # Unique object for unequivocal getattr() defaults.
 _sentinel = object()
@@ -103,7 +90,7 @@ class _CacheHashWrapper(int):
  See GH #613 for more details.
  """
 
- if PY2:
+ if _compat.PY2:
  # For some reason `type(None)` isn't callable in Python 2, but we don't
  # actually need a constructor for None objects, we just need any
  # available function that returns None.
@@ -521,9 +508,9 @@ def _transform_attrs(
  anns = _get_annotations(cls)
 
  if these is not None:
- ca_list = [(name, ca) for name, ca in iteritems(these)]
+ ca_list = [(name, ca) for name, ca in _compat.iteritems(these)]
 
- if not isinstance(these, ordered_dict):
+ if not isinstance(these, _compat.ordered_dict):
  ca_list.sort(key=_counter_getter)
  elif auto_attribs is True:
  ca_names = {
@@ -613,7 +600,7 @@ def _transform_attrs(
  return _Attributes((AttrsClass(attrs), base_attrs, base_attr_map))
 
 
-if PYPY:
+if _compat.PYPY:
 
  def _frozen_setattrs(self, name, value):
  """
@@ -795,7 +782,7 @@ def _create_slots_class(self):
  """
  cd = {
  k: v
- for k, v in iteritems(self._cls_dict)
+ for k, v in _compat.iteritems(self._cls_dict)
  if k not in tuple(self._attr_names) + ("__dict__", "__weakref__")
  }
 
@@ -850,7 +837,7 @@ def _create_slots_class(self):
  # we collect them here and update the class dict
  reused_slots = {
  slot: slot_descriptor
- for slot, slot_descriptor in iteritems(existing_slots)
+ for slot, slot_descriptor in _compat.iteritems(existing_slots)
  if slot in slot_names
  }
  slot_names = [name for name in slot_names if name not in reused_slots]
@@ -893,7 +880,7 @@ def _create_slots_class(self):
  pass
  else:
  if match:
- set_closure_cell(cell, cls)
+ _compat.set_closure_cell(cell, cls)
 
  return cls
 
@@ -1475,7 +1462,7 @@ def attrs(
  .. versionchanged:: 21.1.0 *cmp* undeprecated
  .. versionadded:: 21.3.0 *match_args*
  """
- if auto_detect and PY2:
+ if auto_detect and _compat.PY2:
  raise PythonTooOldError(
  "auto_detect only works on Python 3 and later."
  )
@@ -1591,7 +1578,7 @@ def wrap(cls):
  )
 
  if (
- PY310
+ _compat.PY310
  and match_args
  and not _has_own_attribute(cls, "__match_args__")
  ):
@@ -1614,7 +1601,7 @@ def wrap(cls):
 """
 
 
-if PY2:
+if _compat.PY2:
 
  def _has_frozen_base_class(cls):
  """
@@ -1666,7 +1653,7 @@ def _make_hash(cls, attrs, frozen, cache_hash):
  if not cache_hash:
  hash_def += "):"
  else:
- if not PY2:
+ if not _compat.PY2:
  hash_def += ", *"
 
  hash_def += (
@@ -1864,17 +1851,7 @@ def _add_eq(cls, attrs=None):
  return cls
 
 
-# Thread-local global to track attrs instances which are already being repr'd.
-# This is needed because there is no other (thread-safe) way to pass info
-# about the instances that are already being repr'd through the call stack
-# in order to ensure we don't perform infinite recursion.
-#
-# For instance, if an instance contains a dict which contains that instance,
-# we need to know that we're already repr'ing the outside instance from within
-# the dict's repr() call.
-_already_repring = threading.local()
-
-if HAS_F_STRINGS:
+if _compat.HAS_F_STRINGS:
 
  def _make_repr(attrs, ns, cls):
  unique_filename = "repr"
@@ -1891,7 +1868,7 @@ def _make_repr(attrs, ns, cls):
  for name, r, _ in attr_names_with_reprs
  if r != repr
  }
- globs["_already_repring"] = _already_repring
+ globs["_compat"] = _compat
  globs["AttributeError"] = AttributeError
  globs["NOTHING"] = NOTHING
  attribute_fragments = []
@@ -1919,10 +1896,10 @@ def _make_repr(attrs, ns, cls):
  lines = []
  lines.append("def __repr__(self):")
  lines.append(" try:")
- lines.append(" working_set = _already_repring.working_set")
+ lines.append(" working_set = _compat.repr_context.working_set")
  lines.append(" except AttributeError:")
  lines.append(" working_set = {id(self),}")
- lines.append(" _already_repring.working_set = working_set")
+ lines.append(" _compat.repr_context.working_set = working_set")
  lines.append(" else:")
  lines.append(" if id(self) in working_set:")
  lines.append(" return '...'")
@@ -1962,10 +1939,10 @@ def __repr__(self):
  Automatically created by attrs.
  """
  try:
- working_set = _already_repring.working_set
+ working_set = _compat.repr_context.working_set
  except AttributeError:
  working_set = set()
- _already_repring.working_set = working_set
+ _compat.repr_context.working_set = working_set
 
  if id(self) in working_set:
  return "..."
@@ -2035,7 +2012,7 @@ def fields(cls):
  .. versionchanged:: 16.2.0 Returned tuple allows accessing the fields
  by name.
  """
- if not isclass(cls):
+ if not _compat.isclass(cls):
  raise TypeError("Passed object must be a class.")
  attrs = getattr(cls, "__attrs_attrs__", None)
  if attrs is None:
@@ -2063,14 +2040,14 @@ def fields_dict(cls):
 
  .. versionadded:: 18.1.0
  """
- if not isclass(cls):
+ if not _compat.isclass(cls):
  raise TypeError("Passed object must be a class.")
  attrs = getattr(cls, "__attrs_attrs__", None)
  if attrs is None:
  raise NotAnAttrsClassError(
  "{cls!r} is not an attrs-decorated class.".format(cls=cls)
  )
- return ordered_dict(((a.name, a) for a in attrs))
+ return _compat.ordered_dict(((a.name, a) for a in attrs))
 
 
 def validate(inst):
@@ -2223,7 +2200,7 @@ def _assign_with_converter(attr_name, value_var, has_on_setattr):
  )
 
 
-if PY2:
+if _compat.PY2:
 
  def _unpack_kw_only_py2(attr_name, default=None):
  """
@@ -2497,7 +2474,7 @@ def fmt_setter_with_converter(
  if a.init is True:
  if a.type is not None and a.converter is None:
  annotations[arg_name] = a.type
- elif a.converter is not None and not PY2:
+ elif a.converter is not None and not _compat.PY2:
  # Try to get the type from the converter.
  sig = None
  try:
@@ -2554,7 +2531,7 @@ def fmt_setter_with_converter(
 
  args = ", ".join(args)
  if kw_only_args:
- if PY2:
+ if _compat.PY2:
  lines = _unpack_kw_only_lines_py2(kw_only_args) + lines
 
  args += "%s**_kw_only" % (", " if args else "",) # leading comma
@@ -2673,7 +2650,7 @@ def __init__(
  bound_setattr(
  "metadata",
  (
- metadata_proxy(metadata)
+ _compat.metadata_proxy(metadata)
  if metadata
  else _empty_metadata_singleton
  ),
@@ -2768,7 +2745,7 @@ def _setattrs(self, name_values_pairs):
  else:
  bound_setattr(
  name,
- metadata_proxy(value)
+ _compat.metadata_proxy(value)
  if value
  else _empty_metadata_singleton,
  )
@@ -3044,7 +3021,7 @@ def make_class(name, attrs, bases=(object,), **attributes_arguments):
  if user_init is not None:
  body["__init__"] = user_init
 
- type_ = new_class(name, bases, {}, lambda ns: ns.update(body))
+ type_ = _compat.new_class(name, bases, {}, lambda ns: ns.update(body))
 
  # For pickling to work, the __module__ variable needs to be set to the
  # frame where the class is created. Bypass this step in environments where
@@ -3131,7 +3108,7 @@ def pipe_converter(val):
 
  return val
 
- if not PY2:
+ if not _compat.PY2:
  if not converters:
  # If the converter list is empty, pipe_converter is the identity.
  A = typing.TypeVar("A")