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narrow membership tests against named concrete containers (#4469) - #4816

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shobhitmehro:fix/4469-membership-narrow-named-containers
Open

narrow membership tests against named concrete containers (#4469)#4816
shobhitmehro wants to merge 1 commit into
facebook:mainfrom
shobhitmehro:fix/4469-membership-narrow-named-containers

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@shobhitmehro

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named containers fell through membership narrowing since only inline literals used their element type. this narrows list, set, frozenset, and deque through the same equality-aware path as ==, so it doesn't over-narrow stuff like float against set[int]. abstract containers and custom __contains__ stay untouched since they don't have to follow equality.

fixes #4469

Test Plan

python3 test.py

named containers like `set[str]` fell through membership narrowing since only
inline literals used their element type. this adds a check for concrete
builtin containers (list, set, frozenset, deque) and narrows through the same
equality-aware path as `==`, so types that can still compare equal across a
nominal boundary, like `float` against `set[int]`, don't get over-narrowed.
abstract containers and custom `__contains__` are left alone since their
membership check doesn't have to follow equality.

fixes facebook#4469
@meta-cla meta-cla Bot added the cla signed label Sep 4, 2026
@github-actions github-actions Bot added the size/s label Sep 4, 2026
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meta-codesync Bot commented Sep 4, 2026

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This pull request has been imported. If you are a Meta employee, you can view this in D118862655. (Because this pull request was imported automatically, there will not be any future comments.)

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github-actions Bot commented Sep 4, 2026

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Diff from mypy_primer, showing the effect of this PR on open source code:

============================================================
SUMMARY
============================================================
Total: +13 new errors, -52 fixed errors
By preset: +3/-44 (default), +3/-44 (strict)

Projects with changes (20):
  openlibrary: +2 -3
  rotki: +1 -2
  pytest: +0 -2
  alerta: +3 -3
  pwndbg: +1 -0
  schemathesis: +0 -1
  beartype: +0 -4
  streamlit: +0 -3
  ibis: +0 -2
  zulip: +0 -2
  Tanjun: +0 -1
  websockets: +0 -2
  mypy: +2 -6
  meson: +0 -2
  core: +1 -6
  trio: +0 -2
  sphinx: +0 -2
  spack: +2 -4
  pylint: +1 -4
  archinstall: +0 -1
============================================================

FULL DIFF DETAILS
------------------------------------------------------------

openlibrary (https://github.com/internetarchive/openlibrary)
- ERROR openlibrary/catalog/marc/marc_binary.py:137:23-71: Yielded type `tuple[Unknown | None, Unknown]` is not assignable to declared yield type `tuple[str, BinaryDataField | str]` [invalid-yield]
+ ERROR openlibrary/catalog/marc/marc_binary.py:137:23-71: Yielded type `tuple[str | Unknown | None, Unknown]` is not assignable to declared yield type `tuple[str, BinaryDataField | str]` [invalid-yield]
- ERROR openlibrary/catalog/marc/marc_binary.py:139:23-55: Yielded type `tuple[Unknown | None, BinaryDataField]` is not assignable to declared yield type `tuple[str, BinaryDataField | str]` [invalid-yield]
+ ERROR openlibrary/catalog/marc/marc_binary.py:139:23-55: Yielded type `tuple[str | Unknown | None, BinaryDataField]` is not assignable to declared yield type `tuple[str, BinaryDataField | str]` [invalid-yield]
- ERROR openlibrary/core/lending.py:580:59-72: Argument `object | Unknown` is not assignable to parameter `key` with type `str` in function `dict.get` [bad-argument-type]

rotki (https://github.com/rotki/rotki)
- ERROR rotkehlchen/chain/evm/decoding/yearn/decoder.py:166:58-71: Argument `ChecksumAddress | None` is not assignable to parameter `vault_address` with type `ChecksumAddress` in function `_get_vault_token_name` [bad-argument-type]
+ ERROR rotkehlchen/chain/evm/node_inquirer.py:1674:46-47: Unused `# type: ignore` comment [unused-type-ignore]
- ERROR rotkehlchen/serialization/deserialize.py:756:38-46: Argument `ChainID` is not assignable to parameter `chain_id` with type `Literal[ChainID.BASE, ChainID.OPTIMISM, ChainID.SCROLL]` in function `rotkehlchen.externalapis.etherscan_like.EtherscanLikeApi.get_l1_fee` [bad-argument-type]

pytest (https://github.com/pytest-dev/pytest)
- ERROR src/_pytest/config/__init__.py:594:21-597:22: The type of this argument is unknown [unknown-argument-type]
- ERROR src/_pytest/config/__init__.py:596:25-37: Object of class `NoneType` has no attribute `replace` [missing-attribute]

alerta (https://github.com/alerta/alerta)
- ERROR alerta/models/alarms/alerta.py:149:16-22: Implicit conversion of `Unknown | None` to `bool` is not allowed [implicit-bool]
+ ERROR alerta/models/alarms/alerta.py:149:16-22: Implicit conversion of `str | Unknown | None` to `bool` is not allowed [implicit-bool]
- ERROR alerta/models/alarms/alerta.py:248:16-22: Implicit conversion of `Unknown | None` to `bool` is not allowed [implicit-bool]
+ ERROR alerta/models/alarms/alerta.py:248:16-22: Implicit conversion of `str | Unknown | None` to `bool` is not allowed [implicit-bool]
- ERROR alerta/models/alarms/alerta.py:248:16-48: Implicit conversion of `Unknown | None` to `bool` is not allowed [implicit-bool]
+ ERROR alerta/models/alarms/alerta.py:248:16-48: Implicit conversion of `Literal[''] | bool | Unknown | None` to `bool` is not allowed [implicit-bool]

pwndbg (https://github.com/pwndbg/pwndbg)
+ ERROR pwndbg/aglib/elf.py:445:55-56: Unused `# type: ignore` comment [unused-type-ignore]

schemathesis (https://github.com/schemathesis/schemathesis)
- ERROR src/schemathesis/specs/openapi/coverage/_schema.py:1003:17-20: The type of this argument is unknown [unknown-argument-type]

beartype (https://github.com/beartype/beartype)
- ERROR beartype/_check/convert/_reduce/_nonpep/api/redapinumpy.py:305:55-69: Cannot index into `_IsSubclassFactory` [bad-index]
- ERROR beartype/_check/error/_pep/pep484585/errpep484585container.py:65:13-38: Cannot index into `dict[HintSign, range]` [bad-index]
- ERROR beartype/_check/error/_pep/pep484585/errpep484585container.py:124:9-34: Argument `HintSign | None` is not assignable to parameter `key` with type `HintSign` in function `dict.get` [bad-argument-type]
- ERROR beartype/_check/error/_pep/pep484585/errpep484585mapping.py:58:59-84: Cannot index into `dict[HintSign, range]` [bad-index]

streamlit (https://github.com/streamlit/streamlit)
- ERROR lib/streamlit/elements/heading.py:502:20-27: Returned type `Literal[False] | str | None` is not assignable to declared return type `str` [bad-return]
- ERROR lib/streamlit/elements/lib/built_in_chart_utils.py:820:58-66: `not in` is not supported between `None` and `str` [unsupported-operation]
- ERROR lib/streamlit/elements/lib/built_in_chart_utils.py:821:30-38: Argument `str | None` is not assignable to parameter `value` with type `str` in function `list.remove` [bad-argument-type]

ibis (https://github.com/ibis-project/ibis)
- ERROR ibis/backends/tests/test_udf.py:124:25-26: Cannot index into `dict[LiteralString, int]` [bad-index]
- ERROR ibis/backends/tests/test_udf.py:124:25-26: Cannot set item in `dict[LiteralString, int]` [unsupported-operation]

zulip (https://github.com/zulip/zulip)
- ERROR zerver/actions/message_send.py:586:38-66: Argument `list[tuple[int | Unknown, int | Unknown | None]]` is not assignable to parameter `message_triggered_bot_tuples` with type `list[tuple[int, int]]` in function `RecipientInfoResult.__init__` [bad-argument-type]
- ERROR zproject/computed_settings.py:1148:35-56: Argument `str | None` is not assignable to parameter `value` with type `str` in function `list.remove` [bad-argument-type]

Tanjun (https://github.com/FasterSpeeding/Tanjun)
- ERROR tanjun/context/menu.py:144:16-28: Returned type `CommandType` is not assignable to declared return type `Literal[CommandType.MESSAGE, CommandType.USER]` [bad-return]

websockets (https://github.com/aaugustin/websockets)
- ERROR src/websockets/extensions/permessage_deflate.py:275:46-51: Argument `str | None` is not assignable to parameter `x` with type `Buffer | SupportsIndex | SupportsInt | SupportsTrunc | str` in function `int.__new__` [bad-argument-type]
- ERROR src/websockets/extensions/permessage_deflate.py:285:46-51: Argument `str | None` is not assignable to parameter `x` with type `Buffer | SupportsIndex | SupportsInt | SupportsTrunc | str` in function `int.__new__` [bad-argument-type]

mypy (https://github.com/python/mypy)
- ERROR mypy/semanal.py:4435:49-56: `None` is not subscriptable [unsupported-operation]
- ERROR mypy/stubutil.py:672:21-32: `+` is not supported between `Literal['_']` and `None` [unsupported-operation]
- ERROR mypy/stubutil.py:673:12-41: Implicit conversion of `Literal[True] | str | Unknown | None` to `bool` is not allowed [implicit-bool]
+ ERROR mypy/stubutil.py:673:12-41: Implicit conversion of `Literal[True] | str | None` to `bool` is not allowed [implicit-bool]
- ERROR mypy/stubutil.py:675:16-21: Implicit conversion of `str | Unknown | None` to `bool` is not allowed [implicit-bool]
+ ERROR mypy/stubutil.py:675:16-21: Implicit conversion of `str | None` to `bool` is not allowed [implicit-bool]
- ERROR mypyc/irbuild/util.py:227:13-23: Cannot set item in `MypycAttrs` [unsupported-operation]
- ERROR mypyc/irbuild/util.py:228:19-22: Cannot set item in `dict[MypycAttr, int]` [unsupported-operation]

meson (https://github.com/mesonbuild/meson)
- ERROR mesonbuild/mdevenv.py:236:12-29: `in` is not supported between `Literal['bash']` and `None` [not-iterable]
- ERROR mesonbuild/mdevenv.py:247:14-30: Object of class `NoneType` has no attribute `endswith` [missing-attribute]

core (https://github.com/home-assistant/core)
- ERROR homeassistant/components/deconz/services.py:199:42-57: Argument `str | None` is not assignable to parameter `value` with type `str` in function `list.remove` [bad-argument-type]
- ERROR homeassistant/components/deconz/services.py:206:46-61: Argument `str | None` is not assignable to parameter `value` with type `str` in function `list.remove` [bad-argument-type]
+ ERROR homeassistant/components/mqtt/climate.py:728:41-54: Unnecessary `str()` call; argument is already of type `str` [unnecessary-type-conversion]
- ERROR homeassistant/components/network/__init__.py:85:12-65: Returned type `str | None` is not assignable to declared return type `str` [bad-return]
- ERROR homeassistant/components/shelly/event.py:314:33-43: Argument `Any | None` is not assignable to parameter `event_type` with type `str` in function `homeassistant.components.event.EventEntity._trigger_event` [bad-argument-type]
- ERROR homeassistant/components/tibber/sensor.py:936:33-56: Object of class `NoneType` has no attribute `replace` [missing-attribute]
- ERROR homeassistant/components/yolink/device_trigger.py:90:41-65: Cannot index into `dict[str, set[str]]` [bad-index]

trio (https://github.com/python-trio/trio)
- ERROR src/trio/_highlevel_serve_listeners.py:52:41-50: Cannot index into `Mapping[int, str]` [bad-index]
- ERROR src/trio/_highlevel_serve_listeners.py:53:37-46: Argument `int | None` is not assignable to parameter `code` with type `int` in function `os.strerror` [bad-argument-type]

sphinx (https://github.com/sphinx-doc/sphinx)
- ERROR sphinx/domains/c/_symbol.py:565:50-69: Argument `str | None` is not assignable to parameter `docname` with type `str` in function `Symbol._fill_empty` [bad-argument-type]
- ERROR sphinx/domains/cpp/_symbol.py:941:50-69: Argument `str | None` is not assignable to parameter `docname` with type `str` in function `Symbol._fill_empty` [bad-argument-type]

spack (https://github.com/spack/spack)
- ERROR lib/spack/spack/solver/asp.py:3465:52-62: Argument `str | None` is not assignable to parameter `value` with type `str` in function `list.index` [bad-argument-type]
- ERROR lib/spack/spack/test/cmd/dev_build.py:42:27-63: No matching overload found for function `posixpath.join` called with arguments: (Prefix, object | Unknown) [no-matching-overload]
+ ERROR lib/spack/spack/test/cmd/dev_build.py:60:72-73: Unused `# type: ignore` comment [unused-type-ignore]
+ ERROR lib/spack/spack/test/cmd/dev_build.py:81:72-73: Unused `# type: ignore` comment [unused-type-ignore]
- ERROR lib/spack/spack/test/cmd/dev_build.py:222:27-63: No matching overload found for function `posixpath.join` called with arguments: (Prefix, object | Unknown) [no-matching-overload]
- ERROR lib/spack/spack/test/cmd/dev_build.py:265:27-63: No matching overload found for function `posixpath.join` called with arguments: (Prefix, object | Unknown) [no-matching-overload]

pylint (https://github.com/pycqa/pylint)
- ERROR pylint/checkers/method_args.py:117:16-19: Implicit conversion of `list[str | None]` to `bool` is not allowed [implicit-bool]
+ ERROR pylint/checkers/method_args.py:117:16-19: Implicit conversion of `list[str]` to `bool` is not allowed [implicit-bool]
- ERROR pylint/checkers/nested_min_max.py:105:47-55: Object of class `NodeNG` has no attribute `args` [missing-attribute]
- ERROR pylint/checkers/refactoring/implicit_booleaness_checker.py:224:48-56: Argument `NodeNG | str` is not assignable to parameter `operator` with type `str` in function `ImplicitBooleanessChecker._get_suggestion` [bad-argument-type]
- ERROR pylint/checkers/refactoring/implicit_booleaness_checker.py:244:38-46: Argument `NodeNG | str` is not assignable to parameter `operator` with type `str` in function `ImplicitBooleanessChecker._get_suggestion` [bad-argument-type]

archinstall (https://github.com/archlinux/archinstall)
- ERROR archinstall/lib/menu/list_manager.py:83:43-48: Argument `str | ValueT` is not assignable to parameter `action` with type `str` in function `ListManager.handle_action` [bad-argument-type]

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Membership test against a named set does not narrow <type> | None.

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