Fix method override check

Author: michaelm-openai

mypy/checker.py

@@ -155,7 +155,10 @@
 from mypy.semanal_enum import ENUM_BASES, ENUM_SPECIAL_PROPS
 from mypy.semanal_shared import SemanticAnalyzerCoreInterface
 from mypy.sharedparse import BINARY_MAGIC_METHODS
-from mypy.disallow_str_iteration_state import disallow_str_iteration_state
+from mypy.disallow_str_iteration_state import (
+    STR_ITERATION_PROTOCOL_BASES,
+    disallow_str_iteration_state,
+)
 from mypy.state import state
 from mypy.subtypes import (
     find_member,
@@ -2215,7 +2218,15 @@ def check_method_override(
             )
         )
         found_method_base_classes: list[TypeInfo] = []
+        is_str_or_has_str_base = defn.info.fullname == "builtins.str"
         for base in defn.info.mro[1:]:
+            if disallow_str_iteration_state.disallow_str_iteration:
+                if base.fullname == "builtins.str":
+                    is_str_or_has_str_base = True
+
+                if is_str_or_has_str_base and base.fullname in STR_ITERATION_PROTOCOL_BASES:
+                    continue
+
             result = self.check_method_or_accessor_override_for_base(
                 defn, base, check_override_compatibility
             )

test-data/unit/check-flags.test

@@ -2454,7 +2454,7 @@ f(memoryview(b"asdf"))  # E: Argument 1 to "f" has incompatible type "memoryview
 [case testDisallowStrIteration]
 # flags: --disallow-str-iteration
 from abc import abstractmethod
-from typing import Collection, Container, Iterable, Mapping, Protocol, Sequence, TypeVar, Union
+from typing import Collection, Container, Iterable, Mapping, Protocol, Sequence, SupportsIndex, TypeVar, Union
 
 def takes_str(x: str):
     for ch in x:  # E: Iterating over "str" is disallowed  # N: This is because --disallow-str-iteration is enabled
@@ -2489,6 +2489,7 @@ def takes_str_upper_bound(x: T) -> None:
 
 class StrSubclass(str):
     def __contains__(self, x: object) -> bool: ...
+    def __getitem__(self, key: Union[SupportsIndex, slice], /) -> str: ...
 
 def takes_str_subclass(x: StrSubclass):
     for ch in x:  # E: Iterating over "StrSubclass" is disallowed  # N: This is because --disallow-str-iteration is enabled

test-data/unit/fixtures/str-iter.pyi

@@ -1,7 +1,7 @@
 # Builtins stub used in disallow-str-iteration tests.
 
 
-from typing import Generic, Iterator, Mapping, Sequence, TypeVar, overload
+from typing import Generic, Iterator, Mapping, Sequence, SupportsIndex,TypeVar, overload
 
 _T = TypeVar("_T")
 _KT = TypeVar("_KT")
@@ -20,10 +20,7 @@ class str(Sequence[str]):
     def __iter__(self) -> Iterator[str]: pass
     def __len__(self) -> int: pass
     def __contains__(self, item: object) -> bool: pass
-    @overload
-    def __getitem__(self, i: int, /) -> str: ...
-    @overload
-    def __getitem__(self, s: slice, /) -> Sequence[str]: ...
+    def __getitem__(self, key: SupportsIndex | slice, /) -> str: pass
 
 class list(Sequence[_T], Generic[_T]):
     def __iter__(self) -> Iterator[_T]: pass

test-data/unit/fixtures/typing-str-iter.pyi

@@ -17,29 +17,29 @@ _KT_co = TypeVar("_KT_co", covariant=True)  # Key type covariant containers.
 _VT_co = TypeVar("_VT_co", covariant=True)  # Value type covariant containers.
 _TC = TypeVar("_TC", bound=type[object])
 
-@runtime_checkable
 class Iterable(Protocol[_T_co]):
     @abstractmethod
     def __iter__(self) -> Iterator[_T_co]: ...
 
-@runtime_checkable
 class Iterator(Iterable[_T_co], Protocol[_T_co]):
     @abstractmethod
     def __next__(self) -> _T_co: ...
     def __iter__(self) -> Iterator[_T_co]: ...
 
-@runtime_checkable
 class Container(Protocol[_T_co]):
     # This is generic more on vibes than anything else
     @abstractmethod
     def __contains__(self, x: object, /) -> bool: ...
 
-@runtime_checkable
 class Collection(Iterable[_T_co], Container[_T_co], Protocol[_T_co]):
     # Implement Sized (but don't have it as a base class).
     @abstractmethod
     def __len__(self) -> int: ...
 
+class SupportsIndex(Protocol, metaclass=ABCMeta):
+    @abstractmethod
+    def __index__(self) -> int: ...
+
 class Sequence(Collection[_T_co]):
     @overload
     @abstractmethod