Put type checker global state in separate module

python · ilevkivskyi · May 30, 2025 · Apr 19, 2025 · Apr 19, 2025 · Apr 20, 2025
commit 5b3190a1670ee5ddcc0e9f0d4d92c251d3243a63
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -13,6 +13,7 @@
 from mypy import errorcodes as codes, join, message_registry, nodes, operators
 from mypy.binder import ConditionalTypeBinder, Frame, get_declaration
 from mypy.checker_shared import CheckerScope, TypeCheckerSharedApi, TypeRange
+from mypy.checker_state import checker_state
 from mypy.checkmember import (
     MemberContext,
     analyze_class_attribute_access,
@@ -455,7 +456,7 @@ def check_first_pass(self) -> None:
         Deferred functions will be processed by check_second_pass().
         """
         self.recurse_into_functions = True
-        with state.strict_optional_set(self.options.strict_optional), state.type_checker_set(self):
+        with state.strict_optional_set(self.options.strict_optional), checker_state.set(self):
             self.errors.set_file(
                 self.path, self.tree.fullname, scope=self.tscope, options=self.options
             )
@@ -496,7 +497,7 @@ def check_second_pass(
         This goes through deferred nodes, returning True if there were any.
         """
         self.recurse_into_functions = True
-        with state.strict_optional_set(self.options.strict_optional), state.type_checker_set(self):
+        with state.strict_optional_set(self.options.strict_optional), checker_state.set(self):
             if not todo and not self.deferred_nodes:
                 return False
             self.errors.set_file(

diff --git a/mypy/checker_state.py b/mypy/checker_state.py
@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+from collections.abc import Iterator
+from contextlib import contextmanager
+from typing import Final
+
+from mypy.checker_shared import TypeCheckerSharedApi
+
+# This is global mutable state. Don't add anything here unless there's a very
+# good reason.
+
+
+class TypeCheckerState:
+    # Wrap this in a class since it's faster that using a module-level attribute.
+
+    def __init__(self, type_checker: TypeCheckerSharedApi | None) -> None:
+        # Value varies by file being processed
+        self.type_checker = type_checker
+
+    @contextmanager
+    def set(self, value: TypeCheckerSharedApi) -> Iterator[None]:
+        saved = self.type_checker
+        self.type_checker = value
+        try:
+            yield
+        finally:
+            self.type_checker = saved
+
+
+checker_state: Final = TypeCheckerState(type_checker=None)
diff --git a/mypy/expandtype.py b/mypy/expandtype.py
@@ -4,6 +4,7 @@
 from typing import Final, TypeVar, cast, overload
 
 from mypy.nodes import ARG_STAR, FakeInfo, Var
+from mypy.state import state
 from mypy.types import (
     ANY_STRATEGY,
     AnyType,
@@ -543,8 +544,6 @@ def remove_trivial(types: Iterable[Type]) -> list[Type]:
         * Remove everything else if there is an `object`
         * Remove strict duplicate types
     """
-    from mypy.state import state
-
     removed_none = False
     new_types = []
     all_types = set()

diff --git a/mypy/state.py b/mypy/state.py
@@ -4,19 +4,16 @@
 from contextlib import contextmanager
 from typing import Final
 
-from mypy.checker_shared import TypeCheckerSharedApi
-
 # These are global mutable state. Don't add anything here unless there's a very
 # good reason.
 
 
-class SubtypeState:
+class StrictOptionalState:
     # Wrap this in a class since it's faster that using a module-level attribute.
 
-    def __init__(self, strict_optional: bool, type_checker: TypeCheckerSharedApi | None) -> None:
-        # Values vary by file being processed
+    def __init__(self, strict_optional: bool) -> None:
+        # Value varies by file being processed
         self.strict_optional = strict_optional
-        self.type_checker = type_checker
 
     @contextmanager
     def strict_optional_set(self, value: bool) -> Iterator[None]:
@@ -27,15 +24,6 @@ def strict_optional_set(self, value: bool) -> Iterator[None]:
         finally:
             self.strict_optional = saved
 
-    @contextmanager
-    def type_checker_set(self, value: TypeCheckerSharedApi) -> Iterator[None]:
-        saved = self.type_checker
-        self.type_checker = value
-        try:
-            yield
-        finally:
-            self.type_checker = saved
-
 
-state: Final = SubtypeState(strict_optional=True, type_checker=None)
+state: Final = StrictOptionalState(strict_optional=True)
 find_occurrences: tuple[str, str] | None = None
diff --git a/mypy/subtypes.py b/mypy/subtypes.py
@@ -8,6 +8,7 @@
 import mypy.applytype
 import mypy.constraints
 import mypy.typeops
+from mypy.checker_state import checker_state
 from mypy.erasetype import erase_type
 from mypy.expandtype import (
     expand_self_type,
@@ -1267,7 +1268,7 @@ def find_member(
     class_obj: bool = False,
     is_lvalue: bool = False,
 ) -> Type | None:
-    type_checker = state.type_checker
+    type_checker = checker_state.type_checker
     if type_checker is None:
         # Unfortunately, there are many scenarios where someone calls is_subtype() before
         # type checking phase. In this case we fallback to old (incomplete) logic.

diff --git a/mypy/types.py b/mypy/types.py
@@ -32,6 +32,7 @@
     SymbolNode,
 )
 from mypy.options import Options
+from mypy.state import state
 from mypy.util import IdMapper
 
 T = TypeVar("T")
@@ -2978,8 +2979,6 @@ def accept(self, visitor: TypeVisitor[T]) -> T:
 
     def relevant_items(self) -> list[Type]:
         """Removes NoneTypes from Unions when strict Optional checking is off."""
-        from mypy.state import state
-
         if state.strict_optional:
             return self.items
         else: