fix Support constrained TypeVars #1422

[asukaminato0721]

Summary

Fixes #1422

Adjusted constrained TypeVar handling so return checks accept any constraint and missing-return is suppressed when an isinstance chain covers all constraints, then added a regression test and updated expectations.

Updated constrained TypeVar subtyping to accept any matching constraint.

Added a conservative exhaustive-isinstance check for constrained TypeVar parameters to avoid false missing-return errors.

Test Plan

Added a new return regression test and removed the now-obsolete return-type error expectation.

[Copilot]

Pull request overview

This PR fixes issue #1422 by correctly handling constrained TypeVars in return type checking and missing-return analysis. The key change is recognizing that a constrained TypeVar T = TypeVar("T", int, str) can be satisfied by any of its constraints (not all), and that isinstance chains covering all constraints constitute exhaustive checking.

• Updated subset checking to accept any matching constraint for constrained TypeVars
• Added exhaustive isinstance chain detection to suppress false missing-return errors when all constraints are covered
• Added regression test for constrained TypeVar with isinstance chain

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pyrefly/lib/solver/subset.rs	Changed constrained TypeVar subtype checking from all to any to correctly handle constraint matching
pyrefly/lib/binding/function.rs	Added isinstance chain analysis for constrained TypeVars to detect exhaustive type checking patterns
pyrefly/lib/test/returns.rs	Added regression test for constrained TypeVar with exhaustive isinstance chain
pyrefly/lib/test/generic_restrictions.rs	Removed now-incorrect return type error expectation due to fixed constraint checking

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[github-actions]

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

dulwich (https://github.com/dulwich/dulwich)
- ERROR dulwich/objects.py:243:16-22: Returned type `str` is not assignable to declared return type `PathT` [bad-return]
- ERROR dulwich/objects.py:254:16-24: Returned type `bytes` is not assignable to declared return type `PathT` [bad-return]
- ERROR dulwich/refs.py:1992:12-20: Returned type `dict[Ref, ObjectID | None]` is not assignable to declared return type `T` [bad-return]

hydpy (https://github.com/hydpy-dev/hydpy)
- ERROR hydpy/core/devicetools.py:2541:20-79: Returned type `tuple[(int & t) | (str & t) | None, (int & t) | (str & t) | None] | tuple[t | None, t | None] | t` is not assignable to declared return type `tuple[t | None, t | None]` [bad-return]
+ ERROR hydpy/core/devicetools.py:2541:20-79: Returned type `tuple[int | str | None, int | str | None] | tuple[t | None, t | None] | t` is not assignable to declared return type `tuple[t | None, t | None]` [bad-return]
- ERROR hydpy/core/devicetools.py:2724:20-79: Returned type `tuple[(int & t) | (str & t) | None, (int & t) | (str & t) | None] | tuple[t | None, t | None] | t` is not assignable to declared return type `tuple[t | None, t | None]` [bad-return]
+ ERROR hydpy/core/devicetools.py:2724:20-79: Returned type `tuple[int | str | None, int | str | None] | tuple[t | None, t | None] | t` is not assignable to declared return type `tuple[t | None, t | None]` [bad-return]
+ ERROR hydpy/core/importtools.py:796:32-65: No matching overload found for function `SubmodelAdder.update` called with arguments: (TM_contra, TI_contra, refresh=Literal[False]) [no-matching-overload]
+ ERROR hydpy/core/importtools.py:799:32-84: No matching overload found for function `SubmodelAdder.update` called with arguments: (TM_contra, TI_contra, position=int, refresh=Literal[False]) [no-matching-overload]
+ ERROR hydpy/core/importtools.py:949:29-31: No matching overload found for function `SubmodelAdder.get_wrapped` called with arguments: () [no-matching-overload]
+ ERROR hydpy/core/importtools.py:952:29-31: No matching overload found for function `SubmodelAdder.get_wrapped` called with arguments: () [no-matching-overload]
- ERROR hydpy/core/parametertools.py:1540:20-49: Returned type `float | ndarray[tuple[Any, ...], dtype[float64]]` is not assignable to declared return type `ArrayFloat` [bad-return]
- ERROR hydpy/core/parametertools.py:1542:20-49: Returned type `float | ndarray[tuple[Any, ...], dtype[float64]]` is not assignable to declared return type `ArrayFloat` [bad-return]
- ERROR hydpy/core/parametertools.py:1569:20-49: Returned type `float | ndarray[tuple[Any, ...], dtype[float64]]` is not assignable to declared return type `ArrayFloat` [bad-return]
- ERROR hydpy/core/parametertools.py:1571:20-49: Returned type `float | ndarray[tuple[Any, ...], dtype[float64]]` is not assignable to declared return type `ArrayFloat` [bad-return]
- ERROR hydpy/core/selectiontools.py:715:20-43: Returned type `Node` is not assignable to declared return type `TypeNodeElement` [bad-return]
- ERROR hydpy/core/selectiontools.py:717:20-46: Returned type `Element` is not assignable to declared return type `TypeNodeElement` [bad-return]
- ERROR hydpy/exe/xmltools.py:1868:45-53: Expected class object, got `type[ChangeItem & _TypeGetOrChangeItem]` [invalid-argument]
- ERROR hydpy/exe/xmltools.py:1868:45-53: Expected class object, got `type[GetItem & _TypeGetOrChangeItem]` [invalid-argument]
- ERROR hydpy/exe/xmltools.py:1869:34-38: Argument `ExchangeItem` is not assignable to parameter `object` with type `_TypeGetOrChangeItem` in function `list.append` [bad-argument-type]
- ERROR hydpy/exe/xmltools.py:1873:49-57: Expected class object, got `type[ChangeItem & _TypeGetOrChangeItem]` [invalid-argument]
- ERROR hydpy/exe/xmltools.py:1873:49-57: Expected class object, got `type[GetItem & _TypeGetOrChangeItem]` [invalid-argument]
- ERROR hydpy/exe/xmltools.py:1874:38-42: Argument `ExchangeItem` is not assignable to parameter `object` with type `_TypeGetOrChangeItem` in function `list.append` [bad-argument-type]
- ERROR hydpy/exe/xmltools.py:2373:20-2379:14: `SetItem` is not assignable to variable `item` with type `_TypeSetOrAddOrMultiplyItem` [bad-assignment]

discord.py (https://github.com/Rapptz/discord.py)
- ERROR discord/backoff.py:63:56-61: Default `Literal[False]` is not assignable to parameter `integral` with type `T` [bad-function-definition]

zulip (https://github.com/zulip/zulip)
- ERROR zerver/lib/queue.py:109:17-25: Argument `(ChannelT, Basic.Deliver, BasicProperties, bytes) -> None` is not assignable to parameter `on_message_callback` with type `(Channel, Basic.Deliver, BasicProperties, bytes) -> object` in function `pika.channel.Channel.basic_consume` [bad-argument-type]

koda-validate (https://github.com/keithasaurus/koda-validate)
- ERROR koda_validate/generic.py:321:16-27: Returned type `bytes | str` is not assignable to declared return type `StrOrBytes` [bad-return]
- ERROR koda_validate/generic.py:330:16-27: Returned type `bytes | str` is not assignable to declared return type `StrOrBytes` [bad-return]
- ERROR koda_validate/generic.py:336:16-27: Returned type `bytes | str` is not assignable to declared return type `StrOrBytes` [bad-return]

pyodide (https://github.com/pyodide/pyodide)
- ERROR src/tests/test_static_typing.py:56:20-25: Returned type `float | int | str` is not assignable to declared return type `T` [bad-return]

prefect (https://github.com/PrefectHQ/prefect)
- ERROR src/prefect/utilities/templating.py:199:36-68: `str` is not assignable to variable `template` with type `T` [bad-assignment]
- ERROR src/prefect/utilities/templating.py:201:32-72: `str` is not assignable to variable `template` with type `T` [bad-assignment]
- ERROR src/prefect/utilities/templating.py:323:16-328:10: Returned type `list[dict[str, Any] | Unknown]` is not assignable to declared return type `dict[str, Any] | T` [bad-return]
- ERROR src/prefect/utilities/templating.py:423:24-26: Returned type `Literal['']` is not assignable to declared return type `T` [bad-return]
- ERROR src/prefect/utilities/templating.py:432:36-68: `str` is not assignable to variable `template` with type `T` [bad-assignment]
- ERROR src/prefect/utilities/templating.py:434:36-85: `str` is not assignable to variable `template` with type `T` [bad-assignment]
- ERROR src/prefect/utilities/templating.py:437:16-440:10: Returned type `dict[Unknown, Unknown]` is not assignable to declared return type `T` [bad-return]
- ERROR src/prefect/utilities/templating.py:442:16-83: Returned type `list[Unknown]` is not assignable to declared return type `T` [bad-return]

pandas (https://github.com/pandas-dev/pandas)
- ERROR pandas/core/dtypes/cast.py:409:16-36: Returned type `Index | ndarray[tuple[Any, ...], dtype[signedinteger[_64Bit]]] | NumpyIndexT` is not assignable to declared return type `NumpyIndexT` [bad-return]
- ERROR pandas/core/dtypes/cast.py:411:16-37: Returned type `Index | ndarray[tuple[Any, ...], dtype[unsignedinteger[_64Bit]]] | NumpyIndexT` is not assignable to declared return type `NumpyIndexT` [bad-return]
- ERROR pandas/core/dtypes/cast.py:413:16-38: Returned type `Index | ndarray[tuple[Any, ...], dtype[float64]] | NumpyIndexT` is not assignable to declared return type `NumpyIndexT` [bad-return]
- ERROR pandas/core/resample.py:3143:12-21: Returned type `DatetimeIndex | PeriodIndex | TimedeltaIndex` is not assignable to declared return type `FreqIndexT` [bad-return]
- ERROR pandas/io/stata.py:2253:16-53: Returned type `bytes` is not assignable to declared return type `AnyStr` [bad-return]
- ERROR pandas/io/stata.py:2254:12-48: Returned type `bytes | str` is not assignable to declared return type `AnyStr` [bad-return]

static-frame (https://github.com/static-frame/static-frame)
- ERROR static_frame/core/node_values.py:147:24-155:18: Returned type `Frame[Any, Any, *tuple[Any, ...]]` is not assignable to declared return type `TVContainer_co` [bad-return]
- ERROR static_frame/core/node_values.py:176:20-181:14: Returned type `Series[Any, Any]` is not assignable to declared return type `TVContainer_co` [bad-return]
- ERROR static_frame/core/node_values.py:275:20-284:14: Returned type `Frame[Any, Any, *tuple[Any, ...]] | Index[Any] | IndexHierarchy[*tuple[Any, ...]] | Series[Any, Any]` is not assignable to declared return type `TVContainer_co` [bad-return]

scrapy (https://github.com/scrapy/scrapy)
- ERROR scrapy/utils/datatypes.py:76:16-27: Returned type `bytes | str` is not assignable to declared return type `AnyStr` [bad-return]