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Fix type variable inference for T | Wrapper[T] union patterns#21619

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Fix type variable inference for T | Wrapper[T] union patterns#21619
majidfeiz wants to merge 2 commits into
python:masterfrom
majidfeiz:fix/typevar-union-inference

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@majidfeiz majidfeiz commented Jun 16, 2026

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Fix type variable inference for T | Wrapper[T] union patterns

Summary

Fixes incorrect Never inference when calling a generic function whose parameter type
is a union of a bare TypeVar and a parameterized generic containing that same TypeVar,
such as T | list[T] or T | dict[str, T].

Closes #21615

Problem

Given this function:

from typing import TypeVar, Union, List

T = TypeVar("T")

def f(x: Union[T, List[T]]) -> List[T]: ...

reveal_type(f([1, 2, 3]))  # was: list[Never]  (wrong — also raised a type error)
reveal_type(f([1, 2, 3]))  # now: list[int]     (correct)

Mypy was inferring T = Never for any call where the argument matched the
Wrapper[T] branch of the union instead of the bare T branch.

Root Cause

In _infer_constraints (mypy/constraints.py), when the template is a UnionType
and the direction is SUPERTYPE_OF, mypy calls any_constraints() with one option
per union item:

Branch Constraint produced
T T ≥ list[int] (overly broad)
list[T] T = int (correct)

Because these two options are structurally incompatible, any_constraints() gives up
and returns []. With no constraints, the solver falls back to T = Never.

The existing helper handle_recursive_union() already resolves this correctly: it
tries the non-TypeVar items first (yielding the precise bound T = int from list[T])
and falls back to the bare TypeVar items only when needed. However, it was only invoked
when has_recursive_types(template) was True, which is False for ordinary generic
function signatures.

Fix

Extended the fallback condition in _infer_constraints to also call
handle_recursive_union() when any_constraints() returns empty and the union
template contains:

  1. at least one bare TypeVarType item, and
  2. at least one non-TypeVarType item that itself contains TypeVars (e.g. list[T])

The second condition is the key guard. It ensures the fix applies only to genuine
T | Wrapper[T] patterns and not to unrelated unions such as AnyStr | int, where
int carries no TypeVars and the existing behavior is correct.

# mypy/constraints.py  (simplified diff)

- elif has_recursive_types(template) and not has_recursive_types(actual):
+ elif (
+     has_recursive_types(template)
+     or (
+         any(isinstance(t, TypeVarType) for t in template.items)
+         and any(
+             not isinstance(t, TypeVarType) and has_type_vars(t)
+             for t in template.items
+         )
+     )
+ ) and not has_recursive_types(actual):
      return handle_recursive_union(template, actual, direction)

The docstring of handle_recursive_union() was also updated to document the broader
use case.

Test Plan

  • Updated testUnionInference in test-data/unit/check-inference.test: removed the
    stale expected-error annotation on g(['a']) that was documenting the bug (including
    the comment that called it an "awkward error message").
  • Added testUnionInferenceTypeVarWrapper covering T | list[T] and T | dict[str, T]
    with both scalar and container arguments.
  • Ran the full inference, union, generics, and recursive-types test suites — all pass.
1169 passed, 7 skipped, 1 xfailed   (inference / union / generics)
146  passed, 2 skipped               (recursive types)

Behavior After Fix

from typing import TypeVar, Union, List

T = TypeVar("T")

def f(x: Union[T, List[T]]) -> List[T]: ...

reveal_type(f(1))        # list[int]       ✓
reveal_type(f([]))       # list[Never]     (unchanged — empty list is a separate issue)
reveal_type(f([1, 2, 3]))  # list[int]    ✓  (was list[Never] + type error)
reveal_type(f(["a"]))   # list[str]       ✓  (was list[Never] + type error)

Note: The f([]) case still produces list[Never] because an empty list literal
has type list[Never] before any context is applied. This is a pre-existing
limitation shared with Pyright and is outside the scope of this fix.

majidfeiz and others added 2 commits June 16, 2026 14:15
@majidfeiz
Fix type variable inference for T | Wrapper[T] union patterns
0c7d2b8 
When inferring type arguments for a generic function with a parameter
of the form `T | list[T]` (or any `T | Wrapper[T]` pattern), mypy
incorrectly inferred `T = Never` instead of the element type.

Root cause: `any_constraints()` received two competing options from the
union branches — `T >= list[int]` from the bare `T` branch and `T = int`
from the `list[T]` branch. Because these are structurally incompatible,
`any_constraints()` gave up and returned `[]`, leaving T unconstrained
and causing the solver to fall back to `Never`.

`handle_recursive_union()` already resolves this correctly by trying
parameterized items first (yielding precise bounds like `T = int`) and
falling back to bare TypeVar items only when needed. It was gated behind
`has_recursive_types()`, which returns `False` for ordinary generic
function signatures.

The fix extends the fallback condition to also trigger when the union
contains a bare TypeVar alongside a parameterized item that itself
contains TypeVars (e.g. `list[T]`). The guard deliberately excludes
unions like `AnyStr | int` where the non-TypeVar branch carries no
TypeVars, preventing regressions with constrained TypeVars.

Fixes python#21615
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Diff from mypy_primer, showing the effect of this PR on open source code:

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/states.py:373: error: Argument 1 to "StateGroup" has incompatible type "Collection[Never]"; expected "list[State[Any]]"  [arg-type]
+ src/prefect/states.py:373: error: Argument 1 to "StateGroup" has incompatible type "Collection[Any]"; expected "list[State[Any]]"  [arg-type]
- src/prefect/_internal/states.py:243: error: Argument 1 to "StateGroup" has incompatible type "Collection[Never]"; expected "list[State[Any]]"  [arg-type]
+ src/prefect/_internal/states.py:243: error: Argument 1 to "StateGroup" has incompatible type "Collection[Any]"; expected "list[State[Any]]"  [arg-type]
- src/prefect/task_runners.py:109: error: Overloaded function implementation does not accept all possible parameters of signature 1  [misc]
+ src/prefect/task_runners.py:109: error: Overloaded function implementation cannot satisfy signature 1 due to inconsistencies in how they use type variables  [misc]
+ src/prefect/tasks.py:1185: error: Overloaded function implementation cannot satisfy signature 5 due to inconsistencies in how they use type variables  [misc]
- src/prefect/task_engine.py:1867: error: Overloaded function implementation does not accept all possible parameters of signature 1  [misc]
+ src/prefect/task_engine.py:1867: error: Overloaded function implementation cannot satisfy signature 1 due to inconsistencies in how they use type variables  [misc]

hydra-zen (https://github.com/mit-ll-responsible-ai/hydra-zen)
- src/hydra_zen/typing/_builds_overloads.py:229: error: Overloaded function implementation does not accept all possible parameters of signature 3  [misc]
- src/hydra_zen/typing/_builds_overloads.py:229: error: Overloaded function implementation does not accept all possible parameters of signature 5  [misc]
- src/hydra_zen/typing/_builds_overloads.py:229: error: Overloaded function implementation does not accept all possible parameters of signature 7  [misc]
- src/hydra_zen/typing/_builds_overloads.py:229: error: Overloaded function implementation does not accept all possible parameters of signature 9  [misc]
- src/hydra_zen/typing/_builds_overloads.py:468: error: Overloaded function implementation does not accept all possible parameters of signature 2  [misc]
- src/hydra_zen/typing/_builds_overloads.py:468: error: Overloaded function implementation does not accept all possible parameters of signature 4  [misc]
- src/hydra_zen/typing/_builds_overloads.py:468: error: Overloaded function implementation does not accept all possible parameters of signature 6  [misc]
- src/hydra_zen/typing/_builds_overloads.py:468: error: Overloaded function implementation does not accept all possible parameters of signature 8  [misc]
- src/hydra_zen/typing/_builds_overloads.py:468: error: Overloaded function implementation does not accept all possible parameters of signature 10  [misc]
- src/hydra_zen/typing/_builds_overloads.py:654: error: Overloaded function implementation does not accept all possible parameters of signature 1  [misc]
- src/hydra_zen/typing/_builds_overloads.py:654: error: Overloaded function implementation does not accept all possible parameters of signature 5  [misc]
- src/hydra_zen/structured_configs/_implementations.py:502: error: Need type annotation for "out"  [var-annotated]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 3 due to inconsistencies in how they use type variables  [misc]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 4 due to inconsistencies in how they use type variables  [misc]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 5 due to inconsistencies in how they use type variables  [misc]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 6 due to inconsistencies in how they use type variables  [misc]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 7 due to inconsistencies in how they use type variables  [misc]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 8 due to inconsistencies in how they use type variables  [misc]
+ src/hydra_zen/structured_configs/_implementations.py:1604: error: Overloaded function implementation cannot satisfy signature 9 due to inconsistencies in how they use type variables  [misc]
- tests/annotations/declarations.py:798: error: Not all union combinations were tried because there are too many unions  [misc]
- tests/annotations/declarations.py:800: error: Argument "zen_partial" has incompatible type "bool | None"; expected "Literal[False] | None"  [arg-type]
- tests/annotations/declarations.py:817: error: Not all union combinations were tried because there are too many unions  [misc]
- tests/annotations/declarations.py:819: error: Argument "zen_partial" to "__call__" of "FullBuilds" has incompatible type "bool | None"; expected "Literal[False] | None"  [arg-type]
- tests/annotations/declarations.py:836: error: Not all union combinations were tried because there are too many unions  [misc]
- tests/annotations/declarations.py:836: error: Need type annotation for "pout"  [var-annotated]
- tests/annotations/declarations.py:837: error: Argument 1 to "__call__" of "PBuilds" has incompatible type "Callable[[int], str]"; expected "def (*Never, **Never) -> Never"  [arg-type]
- tests/annotations/declarations.py:876: error: Argument "zen_partial" has incompatible type "bool | None"; expected "Literal[False] | None"  [arg-type]
- tests/annotations/declarations.py:878: error: Unused "type: ignore" comment  [unused-ignore]
- tests/annotations/declarations.py:895: error: Need type annotation for "maybe_full_sig"  [var-annotated]
- tests/annotations/declarations.py:895: error: Argument 1 to "__call__" of "PBuilds" has incompatible type "Callable[[int], Any]"; expected "def (*Never, **Never) -> Never"  [arg-type]
- tests/annotations/declarations.py:895: error: Argument "zen_partial" to "__call__" of "StdBuilds" has incompatible type "bool | None"; expected "Literal[False] | None"  [arg-type]
- tests/annotations/declarations.py:897: error: Unused "type: ignore" comment  [unused-ignore]
- tests/annotations/declarations.py:914: error: Argument "zen_partial" to "__call__" of "FullBuilds" has incompatible type "bool | None"; expected "Literal[False] | None"  [arg-type]
- tests/annotations/declarations.py:916: error: Unused "type: ignore" comment  [unused-ignore]
- tests/annotations/declarations.py:922: error: Argument "zen_partial" to "__call__" of "FullBuilds" has incompatible type "bool | None"; expected "Literal[False] | None"  [arg-type]

antidote (https://github.com/Finistere/antidote)
+ src/antidote/lib/interface_ext/_interface.py:462: error: Value of type variable "Weight" of "__register_implementation" of "ImplementsImpl" cannot be "object"  [type-var]
+ src/antidote/lib/interface_ext/_interface.py:464: error: Value of type variable "Weight" of "create_conditions" cannot be "object"  [type-var]
+ src/antidote/lib/interface_ext/__init__.py:1266: error: Signature of "when" incompatible with supertype "implements"  [override]
+ src/antidote/lib/interface_ext/__init__.py:1266: note:      Superclass:
+ src/antidote/lib/interface_ext/__init__.py:1266: note:          def [Weight: ImplementationWeight] when(self, *conditions: Predicate[Weight] | Predicate[NeutralWeight] | Weight | NeutralWeight | bool | None, qualified_by: object = ...) -> Callable[[Any], Any]
+ src/antidote/lib/interface_ext/__init__.py:1266: note:      Subclass:
+ src/antidote/lib/interface_ext/__init__.py:1266: note:          def [Weight: ImplementationWeight] when(self, *conditions: Predicate[Weight] | Predicate[NeutralWeight] | Weight | NeutralWeight | bool | None, qualified_by: object = ...) -> Callable[[C], C]
+ src/antidote/lib/interface_ext/__init__.py:1372: error: Signature of "when" incompatible with supertype "implements"  [override]
+ src/antidote/lib/interface_ext/__init__.py:1372: note:      Superclass:
+ src/antidote/lib/interface_ext/__init__.py:1372: note:          def [Weight: ImplementationWeight] when(self, *conditions: Predicate[Weight] | Predicate[NeutralWeight] | Weight | NeutralWeight | bool | None, qualified_by: object = ...) -> Callable[[Any], Any]
+ src/antidote/lib/interface_ext/__init__.py:1372: note:      Subclass:
+ src/antidote/lib/interface_ext/__init__.py:1372: note:          def [Weight: ImplementationWeight] when(self, *conditions: Predicate[Weight] | Predicate[NeutralWeight] | Weight | NeutralWeight | bool | None, qualified_by: object = ...) -> Callable[[T], T]
+ tests/lib/interface/test_lazy.py:79: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:401: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:405: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:410: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:414: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:614: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:626: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:641: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_lazy.py:652: error: Value of type variable "Weight" of "when" of "LazyImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:72: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:275: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:279: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:284: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:491: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:501: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:515: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_function.py:525: error: Value of type variable "Weight" of "when" of "FunctionImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_custom.py:213: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Dummy"  [type-var]
+ tests/lib/interface/test_conditions.py:54: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "bool"  [type-var]
+ tests/lib/interface/test_conditions.py:58: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "bool"  [type-var]
+ tests/lib/interface/test_conditions.py:70: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:78: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:116: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "OnlyIf"  [type-var]
+ tests/lib/interface/test_conditions.py:120: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "OnlyIf"  [type-var]
+ tests/lib/interface/test_conditions.py:132: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "object"  [type-var]
+ tests/lib/interface/test_conditions.py:136: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "object"  [type-var]
+ tests/lib/interface/test_conditions.py:193: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | OnlyIf | bool | None"  [type-var]
+ tests/lib/interface/test_conditions.py:217: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:278: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:284: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "WeightAlt | None"  [type-var]
+ tests/lib/interface/test_conditions.py:294: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:300: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:306: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_conditions.py:312: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_class.py:686: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_class.py:691: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_class.py:697: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_class.py:702: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "Weight | None"  [type-var]
+ tests/lib/interface/test_class.py:774: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "bool"  [type-var]
+ tests/lib/interface/test_class.py:780: error: Value of type variable "Weight" of "when" of "ClassImplements" cannot be "bool"  [type-var]

discord.py (https://github.com/Rapptz/discord.py)
- discord/app_commands/commands.py:1013: error: Argument 1 to "maybe_coroutine" has incompatible type "Callable[[Interaction[ClientT]], Coroutine[Any, Any, bool]]"; expected "Callable[[Interaction[Client]], Never | Awaitable[Never]]"  [arg-type]
- discord/ext/commands/cog.py:710: error: Argument 1 to "maybe_coroutine" has incompatible type "Callable[[], Coroutine[Any, Any, None]]"; expected "Callable[[], Never | Awaitable[Never]]"  [arg-type]
- discord/ext/commands/cog.py:727: error: Argument 1 to "maybe_coroutine" has incompatible type "Callable[[], Coroutine[Any, Any, None]]"; expected "Callable[[], Never | Awaitable[Never]]"  [arg-type]
- discord/ext/commands/cog.py:780: error: Argument 1 to "maybe_coroutine" has incompatible type "Callable[[], Coroutine[Any, Any, None]]"; expected "Callable[[], Never | Awaitable[Never]]"  [arg-type]
- discord/ext/commands/hybrid.py:420: error: Argument 1 to "maybe_coroutine" has incompatible type "Callable[[Interaction[ClientT]], Coroutine[Any, Any, bool]]"; expected "Callable[[Interaction[Client]], Never | Awaitable[Never]]"  [arg-type]

Tanjun (https://github.com/FasterSpeeding/Tanjun)
- tanjun/hooks.py:389: error: Need type annotation for "results" (hint: "results: list[<type>] = ...")  [var-annotated]
- tanjun/dependencies/data.py:220: error: Argument "callback" to "inject" has incompatible type "Callable[..., Coroutine[Any, Any, _T]]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/dependencies/data.py:347: error: Argument "callback" to "inject" has incompatible type "Callable[..., Coroutine[Any, Any, _T]]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/_internal/__init__.py:82: error: Need type annotation for "result"  [var-annotated]
- tanjun/_internal/__init__.py:83: error: Statement is unreachable  [unreachable]
- tanjun/schedules.py:347: error: Argument 1 to "call_with_async_di" of "Client" has incompatible type "_CallbackSigT"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/schedules.py:373: error: Argument 1 to "call_with_async_di" of "Client" has incompatible type "Callable[..., Coroutine[Any, Any, None]]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/schedules.py:396: error: Argument 1 to "call_with_async_di" of "Client" has incompatible type "Callable[..., Coroutine[Any, Any, None]]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/schedules.py:1067: error: Argument 1 to "call_with_async_di" of "Client" has incompatible type "_CallbackSigT"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/checks.py:1140: error: Statement is unreachable  [unreachable]
- tanjun/commands/slash.py:3191: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "_SlashCallbackSigT"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/commands/slash.py:3235: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "def (AutocompleteContext, str, /, *Any, **Any) -> Coroutine[Any, Any, None] | def (AutocompleteContext, float, /, *Any, **Any) -> Coroutine[Any, Any, None] | def (AutocompleteContext, int, /, *Any, **Any) -> Coroutine[Any, Any, None]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/commands/message.py:346: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "_MessageCallbackSigT"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/commands/menu.py:689: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "_AnyMenuCallbackSigT"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]
- tanjun/clients.py:2294: error: Argument 1 to "call_with_async_di" of "Context" has incompatible type "def (MessageContext, /, *Any, **Any) -> Coroutine[Any, Any, Iterable[str]]"; expected "Callable[..., Coroutine[Any, Any, Never] | Never]"  [arg-type]

pandas-stubs (https://github.com/pandas-dev/pandas-stubs)
+ tests/series/complex/test_sub.py:89: error: Expression is of type "Never", not "Series[complex]"  [assert-type]
+ tests/series/complex/test_sub.py:90: error: Statement is unreachable  [unreachable]
+ tests/indexes/complex/test_sub.py:54: error: Expression is of type "Never", not "Index[complex]"  [assert-type]
+ tests/indexes/complex/test_sub.py:55: error: Statement is unreachable  [unreachable]

sympy (https://github.com/sympy/sympy)
+ sympy/polys/euclidtools.py:799: error: Overloaded function implementation cannot satisfy signature 2 due to inconsistencies in how they use type variables  [misc]

anyio (https://github.com/agronholm/anyio)
+ src/anyio/_core/_tempfile.py:97: error: Value of type variable "AnyStr" of "TemporaryFile" cannot be "str | None"  [type-var]
+ src/anyio/_core/_tempfile.py:97: error: Not all union combinations were tried because there are too many unions  [misc]
+ src/anyio/_core/_tempfile.py:98: error: Argument 1 to "TemporaryFile" has incompatible type "Literal['r+', '+r', 'rt+', 'r+t', '+rt', 'tr+', 't+r', '+tr', 'w+', '+w', 'wt+', 'w+t', '+wt', 'tw+', 't+w', '+tw', 'a+', '+a', 'at+', 'a+t', '+at', 'ta+', 't+a', '+ta', 'x+', '+x', 'xt+', 'x+t', '+xt', 'tx+', 't+x', '+tx', 'w', 'wt', 'tw', 'a', 'at', 'ta', 'x', 'xt', 'tx', 'r', 'rt', 'tr', 'U', 'rU', 'Ur', 'rtU', 'rUt', 'Urt', 'trU', 'tUr', 'Utr', 'rb+', 'r+b', '+rb', 'br+', 'b+r', '+br', 'wb+', 'w+b', '+wb', 'bw+', 'b+w', '+bw', 'ab+', 'a+b', '+ab', 'ba+', 'b+a', '+ba', 'xb+', 'x+b', '+xb', 'bx+', 'b+x', '+bx', 'rb', 'br', 'rbU', 'rUb', 'Urb', 'brU', 'bUr', 'Ubr', 'wb', 'bw', 'ab', 'ba', 'xb', 'bx']"; expected "Literal['r+', '+r', 'rt+', 'r+t', '+rt', 'tr+', 't+r', '+tr', 'w+', '+w', 'wt+', 'w+t', '+wt', 'tw+', 't+w', '+tw', 'a+', '+a', 'at+', 'a+t', '+at', 'ta+', 't+a', '+ta', 'x+', '+x', 'xt+', 'x+t', '+xt', 'tx+', 't+x', '+tx'] | Literal['w', 'wt', 'tw', 'a', 'at', 'ta', 'x', 'xt', 'tx'] | Literal['r', 'rt', 'tr', 'U', 'rU', 'Ur', 'rtU', 'rUt', 'Urt', 'trU', 'tUr', 'Utr']"  [arg-type]
+ src/anyio/_core/_tempfile.py:108: error: Argument 1 to "AsyncFile" has incompatible type "TextIOWrapper[_WrappedBuffer]"; expected "IO[bytes]"  [arg-type]

xarray (https://github.com/pydata/xarray)
+ xarray/conventions.py: note: In function "decode_cf_variables":
+ xarray/conventions.py:413: error: Argument "concat_characters" to "decode_cf_variable" has incompatible type "object"; expected "bool"  [arg-type]
+ xarray/conventions.py:414: error: Argument "mask_and_scale" to "decode_cf_variable" has incompatible type "object"; expected "bool"  [arg-type]
+ xarray/conventions.py:418: error: Argument "stack_char_dim" to "decode_cf_variable" has incompatible type "object | Any"; expected "bool"  [arg-type]
+ xarray/conventions.py:419: error: Argument "use_cftime" to "decode_cf_variable" has incompatible type "bool | Mapping[str, bool] | None"; expected "bool | None"  [arg-type]
+ xarray/conventions.py:420: error: Argument "decode_timedelta" to "decode_cf_variable" has incompatible type "CFTimedeltaCoder | bool | Mapping[str, bool | CFTimedeltaCoder] | None"; expected "bool | CFTimedeltaCoder | None"  [arg-type]
+ xarray/conventions.py:420: error: Argument "decode_timedelta" to "decode_cf_variable" has incompatible type "Mapping[str, bool | CFTimedeltaCoder] | bool | CFTimedeltaCoder | None"; expected "bool | CFTimedeltaCoder | None"  [arg-type]

ibis (https://github.com/ibis-project/ibis)
+ ibis/common/egraph.py:733: error: Item "function" of "Callable[..., Any] | Pattern | Variable" has no attribute "substitute"  [union-attr]
- ibis/common/egraph.py:731: error: Need type annotation for "rewrite"  [var-annotated]
- ibis/common/egraph.py:731: error: Argument 1 to "promote_list" has incompatible type "list[Rewrite]"; expected "Iterable[Never]"  [arg-type]
- ibis/expr/types/strings.py:973: error: Need type annotation for "pattern"  [var-annotated]
- ibis/expr/types/strings.py:975: error: Argument 1 to "promote_list" has incompatible type "str | StringValue | Deferred | Iterable[str | StringValue | Deferred]"; expected "Iterable[Never]"  [arg-type]
+ ibis/expr/types/strings.py:974: error: Argument 2 to "StringSQLLike" has incompatible type "str | StringValue | Deferred"; expected "Value[String, Any]"  [arg-type]
- ibis/expr/types/strings.py:1019: error: Need type annotation for "pattern"  [var-annotated]
- ibis/expr/types/strings.py:1021: error: Argument 1 to "promote_list" has incompatible type "str | StringValue | Deferred | Iterable[str | StringValue | Deferred]"; expected "Iterable[Never]"  [arg-type]
+ ibis/expr/types/strings.py:1020: error: Argument 2 to "StringSQLILike" has incompatible type "str | StringValue | Deferred"; expected "Value[String, Any]"  [arg-type]
- ibis/expr/types/relations.py:1141: error: Need type annotation for "arg"  [var-annotated]
- ibis/expr/types/relations.py:1143: error: Argument 1 to "promote_list" has incompatible type "Sequence[str | int]"; expected "Iterable[Never]"  [arg-type]
- ibis/expr/types/relations.py:4938: error: Argument 1 to "promote_list" has incompatible type "str | Iterable[str] | Selector"; expected "Selector | Iterable[Selector]"  [arg-type]
+ ibis/expr/types/relations.py:4940: error: Argument 1 to "_to_selector" has incompatible type "list[object]"; expected "str | Selector | Column | Sequence[str | Selector | Column]"  [arg-type]
- ibis/backends/flink/ddl.py:96: error: Argument 1 to "promote_list" has incompatible type "str | Sequence[str] | None"; expected "Iterable[None] | None"  [arg-type]

graphql-core (https://github.com/graphql-python/graphql-core)
+ src/graphql/type/definition.py:1263: error: Unused "type: ignore" comment  [unused-ignore]

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Mypy infers strange types for unions of T | Wrapper[T]

2 participants

@majidfeiz @ilevkivskyi