[ty] Use separate Rust types for bound and unbound type variables#19796
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[ty] Use separate Rust types for bound and unbound type variables#19796
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primarily for legacy typevar defaults
dcreager
requested review from
AlexWaygood,
MichaReiser,
carljm and
sharkdp
as code owners
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@carljm and I concurrently realized that we didn't need a new from typing import Generic, TypeVar
T = TypeVar("T")
U = TypeVar("U", default=T)The use of
This was a good suggestion, which I've implemented. |
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Doh! The size of |
* origin/main: [ty] Implemented support for "rename" language server feature (#19551) [ty] Reduce size of member table (#19572) [ty] Move server capabilities creation (#19798) [ty] Repurpose `FunctionType.into_bound_method_type` to return `BoundMethodType` (#19793) [ty] Validate writes to `TypedDict` keys (#19782) [ty] Add support for using the test command emitted when a mdtest fails (#19794)
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Diagnostic diff on typing conformance testsChanges were detected when running ty on typing conformance tests--- old-output.txt 2025-08-11 17:44:43.096472962 +0000
+++ new-output.txt 2025-08-11 17:44:43.163473111 +0000
@@ -84,9 +84,9 @@
aliases_typealiastype.py:63:42: error[invalid-type-form] Boolean operations are not allowed in type expressions
aliases_typealiastype.py:64:42: error[invalid-type-form] F-strings are not allowed in type expressions
aliases_typealiastype.py:66:47: error[unresolved-reference] Name `BadAlias21` used when not defined
-aliases_variance.py:18:24: error[non-subscriptable] Cannot subscript object of type `<class 'ClassA[T_co]'>` with no `__class_getitem__` method
-aliases_variance.py:28:16: error[non-subscriptable] Cannot subscript object of type `<class 'ClassA[T_co]'>` with no `__class_getitem__` method
-aliases_variance.py:44:16: error[non-subscriptable] Cannot subscript object of type `<class 'ClassB[T_co, T_contra]'>` with no `__class_getitem__` method
+aliases_variance.py:18:24: error[non-subscriptable] Cannot subscript object of type `<class 'ClassA[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+aliases_variance.py:28:16: error[non-subscriptable] Cannot subscript object of type `<class 'ClassA[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+aliases_variance.py:44:16: error[non-subscriptable] Cannot subscript object of type `<class 'ClassB[typing.TypeVar("T_co"), typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
annotations_forward_refs.py:22:7: error[unresolved-reference] Name `ClassA` used when not defined
annotations_forward_refs.py:23:12: error[unresolved-reference] Name `ClassA` used when not defined
annotations_forward_refs.py:49:10: error[invalid-type-form] Variable of type `Literal[1]` is not allowed in a type expression
@@ -400,7 +400,7 @@
generics_defaults_referential.py:95:1: error[type-assertion-failure] Argument does not have asserted type `@Todo`
generics_defaults_specialization.py:26:5: error[type-assertion-failure] Argument does not have asserted type `SomethingWithNoDefaults[int, str]`
generics_defaults_specialization.py:27:5: error[type-assertion-failure] Argument does not have asserted type `SomethingWithNoDefaults[int, bool]`
-generics_defaults_specialization.py:30:1: error[non-subscriptable] Cannot subscript object of type `<class 'SomethingWithNoDefaults[int, DefaultStrT]'>` with no `__class_getitem__` method
+generics_defaults_specialization.py:30:1: error[non-subscriptable] Cannot subscript object of type `<class 'SomethingWithNoDefaults[int, typing.TypeVar("DefaultStrT", default=str)]'>` with no `__class_getitem__` method
generics_defaults_specialization.py:45:1: error[type-assertion-failure] Argument does not have asserted type `@Todo`
generics_paramspec_basic.py:27:38: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `int`
generics_paramspec_components.py:83:18: error[parameter-already-assigned] Multiple values provided for parameter 1 (`x`) of function `foo`
@@ -436,16 +436,16 @@
generics_self_advanced.py:18:1: error[type-assertion-failure] Argument does not have asserted type `ParentA`
generics_self_advanced.py:19:1: error[type-assertion-failure] Argument does not have asserted type `ChildA`
generics_self_advanced.py:28:25: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Self@method1`
-generics_self_advanced.py:35:9: error[type-assertion-failure] Argument does not have asserted type `Self`
-generics_self_advanced.py:36:9: error[type-assertion-failure] Argument does not have asserted type `list[Self]`
-generics_self_advanced.py:37:9: error[type-assertion-failure] Argument does not have asserted type `Self`
-generics_self_advanced.py:38:9: error[type-assertion-failure] Argument does not have asserted type `Self`
-generics_self_advanced.py:43:9: error[type-assertion-failure] Argument does not have asserted type `list[Self]`
-generics_self_advanced.py:44:9: error[type-assertion-failure] Argument does not have asserted type `Self`
-generics_self_advanced.py:45:9: error[type-assertion-failure] Argument does not have asserted type `Self`
-generics_self_attributes.py:26:33: error[invalid-argument-type] Argument is incorrect: Expected `Self | None`, found `LinkedList[int]`
-generics_self_attributes.py:29:5: error[invalid-assignment] Object of type `OrdinalLinkedList` is not assignable to attribute `next` of type `Self | None`
-generics_self_attributes.py:32:5: error[invalid-assignment] Object of type `LinkedList[int]` is not assignable to attribute `next` of type `Self | None`
+generics_self_advanced.py:35:9: error[type-assertion-failure] Argument does not have asserted type `typing.Self`
+generics_self_advanced.py:36:9: error[type-assertion-failure] Argument does not have asserted type `list[typing.Self]`
+generics_self_advanced.py:37:9: error[type-assertion-failure] Argument does not have asserted type `typing.Self`
+generics_self_advanced.py:38:9: error[type-assertion-failure] Argument does not have asserted type `typing.Self`
+generics_self_advanced.py:43:9: error[type-assertion-failure] Argument does not have asserted type `list[typing.Self]`
+generics_self_advanced.py:44:9: error[type-assertion-failure] Argument does not have asserted type `typing.Self`
+generics_self_advanced.py:45:9: error[type-assertion-failure] Argument does not have asserted type `typing.Self`
+generics_self_attributes.py:26:33: error[invalid-argument-type] Argument is incorrect: Expected `typing.Self | None`, found `LinkedList[int]`
+generics_self_attributes.py:29:5: error[invalid-assignment] Object of type `OrdinalLinkedList` is not assignable to attribute `next` of type `typing.Self | None`
+generics_self_attributes.py:32:5: error[invalid-assignment] Object of type `LinkedList[int]` is not assignable to attribute `next` of type `typing.Self | None`
generics_self_basic.py:14:9: error[type-assertion-failure] Argument does not have asserted type `Self@set_scale`
generics_self_basic.py:20:16: error[invalid-return-type] Return type does not match returned value: expected `Self@method2`, found `Shape`
generics_self_basic.py:33:16: error[invalid-return-type] Return type does not match returned value: expected `Self@cls_method2`, found `Shape`
@@ -473,7 +473,7 @@
generics_self_usage.py:121:37: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Self@__new__`
generics_self_usage.py:125:37: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `list[Self@__mul__]`
generics_syntax_compatibility.py:23:38: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `V@ClassC | K@method1`
-generics_syntax_compatibility.py:26:41: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `M@method2 | K`
+generics_syntax_compatibility.py:26:41: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `M@method2 | K@method2`
generics_syntax_declarations.py:17:1: error[invalid-generic-class] Cannot both inherit from `typing.Generic` and use PEP 695 type variables
generics_syntax_declarations.py:25:20: error[invalid-generic-class] Cannot both inherit from subscripted `Protocol` and use PEP 695 type variables
generics_syntax_declarations.py:32:9: error[unresolved-attribute] Type `T@ClassD` has no attribute `is_integer`
@@ -580,20 +580,20 @@
generics_variance.py:14:6: error[invalid-legacy-type-variable] A legacy `typing.TypeVar` cannot be both covariant and contravariant
generics_variance.py:26:27: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Iterator[T_co@ImmutableList]`
generics_variance.py:57:28: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `B_co@func`
-generics_variance.py:175:25: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:175:35: error[non-subscriptable] Cannot subscript object of type `<class 'Co[T_co]'>` with no `__class_getitem__` method
-generics_variance.py:179:29: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:179:39: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:183:21: error[non-subscriptable] Cannot subscript object of type `<class 'Co[T_co]'>` with no `__class_getitem__` method
-generics_variance.py:183:27: error[non-subscriptable] Cannot subscript object of type `<class 'Co[T_co]'>` with no `__class_getitem__` method
-generics_variance.py:187:25: error[non-subscriptable] Cannot subscript object of type `<class 'Co[T_co]'>` with no `__class_getitem__` method
-generics_variance.py:187:31: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:191:33: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:191:43: error[non-subscriptable] Cannot subscript object of type `<class 'Co[T_co]'>` with no `__class_getitem__` method
-generics_variance.py:191:49: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:196:5: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:196:15: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
-generics_variance.py:196:25: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[T_contra]'>` with no `__class_getitem__` method
+generics_variance.py:175:25: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:175:35: error[non-subscriptable] Cannot subscript object of type `<class 'Co[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+generics_variance.py:179:29: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:179:39: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:183:21: error[non-subscriptable] Cannot subscript object of type `<class 'Co[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+generics_variance.py:183:27: error[non-subscriptable] Cannot subscript object of type `<class 'Co[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+generics_variance.py:187:25: error[non-subscriptable] Cannot subscript object of type `<class 'Co[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+generics_variance.py:187:31: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:191:33: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:191:43: error[non-subscriptable] Cannot subscript object of type `<class 'Co[typing.TypeVar("T_co")]'>` with no `__class_getitem__` method
+generics_variance.py:191:49: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:196:5: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:196:15: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
+generics_variance.py:196:25: error[non-subscriptable] Cannot subscript object of type `<class 'Contra[typing.TypeVar("T_contra")]'>` with no `__class_getitem__` method
generics_variance_inference.py:19:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `T3@ClassA`
generics_variance_inference.py:24:5: error[invalid-assignment] Object of type `ClassA[int | float, int, int]` is not assignable to `ClassA[int, int, int]`
generics_variance_inference.py:25:5: error[invalid-assignment] Object of type `ClassA[int | float, int, int]` is not assignable to `ClassA[int | float, int | float, int]` |
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| Lint rule | Added | Removed | Changed |
|---|---|---|---|
unresolved-attribute |
0 | 2,856 | 0 |
invalid-argument-type |
37 | 746 | 21 |
invalid-return-type |
0 | 166 | 1 |
possibly-unbound-attribute |
5 | 43 | 0 |
non-subscriptable |
0 | 0 | 20 |
invalid-assignment |
0 | 14 | 0 |
no-matching-overload |
3 | 0 | 0 |
unused-ignore-comment |
2 | 0 | 0 |
call-non-callable |
1 | 0 | 0 |
not-iterable |
0 | 1 | 0 |
unsupported-operator |
0 | 1 | 0 |
| Total | 48 | 3,827 | 42 |
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Author
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The with some extra debug statements, the two typevars actually have different binding contexts: because the Going to dig into this some more |
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The reason for this was interesting! Whenever we use a typevar in a type context, we need to determine if the typevar is bound at that point in the source. We walk through the enclosing scopes, to see if any of them are a generic class/function that binds the typevar in question. That requires knowing the generic context of said classes/functions. For a generic function, we find the infered type for the definition (which should be a This works because we create a EXCEPT! We don't include the implementation when producing the signature of a function! This is almost always what you want. But not here! For a typevar reference inside the implementation body of an overloaded function, we would grab the signature of last non-implementation overload, and use that as the binding context. The fix is to add an additional method on |
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The remaining new ecosystem diagnostics look to all be from either:
|
carljm
approved these changes
Aug 8, 2025
crates/ty_ide/src/hover.rs
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| typing.TypeVar[T: int = bool] | ||
| --------------------------------------------- | ||
| ```python | ||
| T@Alias | ||
| typing.TypeVar[T: int = bool] |
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Does this display change indicate that we now consider T unbound here? Is that right? The type parameter to list is a type expression, so I would expect this use of T to be inferred as Type::TypeVar, and T should be bound to the type alias context.
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It always was unbound, we just couldn't see it before! You're right that it should be bound, but we're not creating GenericContexts for type aliases yet [playground]:
type Alias[T] = list[T]
reveal_type(Alias[int]) # revealed: @TodoOnce type aliases have a generic context, we can update enclosing_generic_scopes to return those, and then this will become bound as it should. I'll add a TODO comment here.
| func() | ||
| except exception_type as e: | ||
| reveal_type(e) # revealed: T'instance | ||
| reveal_type(e) # revealed: T'instance@silence |
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Clearly it pre-exists this PR, but where does the 'instance in this typevar's name come from?
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T is bound to an exception type, but the actual caught expression will be an instance of that type. So it's not correct to reveal T@silence here, since that would be the type of type(e). Type::to_instance will synthesize a new typevar with this modified name. Though a better representation might be letting NominalInstance wrap a typevar?
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Having NominalInstance wrap a typevar seems like an awkward representation, since it would only be valid for a typevar with upper bound of type[...]. I feel like what we're doing here makes sense, just hard to come up with a good name for it. Not something to worry about in this PR.
As a side note, this code example seems quite difficult for type checkers:
from typing import Callable
def silence[T: type[BaseException]](
func: Callable[[], None],
exception_type: T,
) -> T | None:
try:
func()
except exception_type as e:
reveal_type(e)
return e # should be a type error, only returning `type(e)` would be validPyright reveals BaseException*, which is kind of reasonable but what does the * mean? (I think it means "best guess type", which is treated as dynamic.) And then it allows return e, which is clearly a false negative.
Mypy doesn't even allow the except exception_type as e, and then reveals Any.
Pyrefly just panics.
The next interesting bit is to try replacing return e with return type(e), which in principle should be valid. We don't allow that, because we don't track enough metadata to round-trip the T'instance typevar back to T in to_meta_type. (I guess your suggestion of wrapping T rather than synthesizing a new typevar might allow us to fix that.)
Anyway, this is all just musing because it's interesting, not relevant to this PR!
crates/ty_python_semantic/resources/mdtest/generics/legacy/functions.md
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* main: (31 commits) Add AIR301 rule (#17707) Avoid underflow in default ranges before a BOM (#19839) Update actions/download-artifact digest to de96f46 (#19852) Update docker/login-action action to v3.5.0 (#19860) Update rui314/setup-mold digest to 7344740 (#19853) Update cargo-bins/cargo-binstall action to v1.14.4 (#19855) Update actions/cache action to v4.2.4 (#19854) Update Rust crate hashbrown to v0.15.5 (#19858) Update Rust crate camino to v1.1.11 (#19857) Update Rust crate proc-macro2 to v1.0.96 (#19859) Update dependency ruff to v0.12.8 (#19856) SIM905: Fix handling of U+001C..U+001F whitespace (#19849) RUF064: offer a safe fix for multi-digit zeros (#19847) Clean up unused rendering code in `ruff_linter` (#19832) [ty] Add Salsa caching to `TupleType::to_class_type` (#19840) [ty] Handle cycles when finding implicit attributes (#19833) [ty] fix goto-definition on imports (#19834) [ty] Implement stdlib stub mapping (#19529) [`flake8-comprehensions`] Fix false positive for `C420` with attribute, subscript, or slice assignment targets (#19513) [ty] Implement module-level `__getattr__` support (#19791) ...
Co-authored-by: Carl Meyer <[email protected]>
…eager/bound-typevar * origin/dcreager/bound-typevar: Apply suggestions from code review
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* origin/main: [ty] Use separate Rust types for bound and unbound type variables (#19796)
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* dcreager/bound-typevar: (41 commits) [ty] Use separate Rust types for bound and unbound type variables (#19796) fix ide tests better unbound typevar rendering Apply suggestions from code review [ty] Add `static-frame` as a walltime benchmark (#19844) add explanatory comment [ty] Update goto range for attribute access to only target the attribute (#19848) remove unneeded ord add TODO for broken hover test better PEP 695 binding context Add AIR301 rule (#17707) Avoid underflow in default ranges before a BOM (#19839) Update actions/download-artifact digest to de96f46 (#19852) Update docker/login-action action to v3.5.0 (#19860) Update rui314/setup-mold digest to 7344740 (#19853) Update cargo-bins/cargo-binstall action to v1.14.4 (#19855) Update actions/cache action to v4.2.4 (#19854) Update Rust crate hashbrown to v0.15.5 (#19858) Update Rust crate camino to v1.1.11 (#19857) Update Rust crate proc-macro2 to v1.0.96 (#19859) ...
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This PR creates separate Rust types for bound and unbound type variables, as proposed in astral-sh/ty#926.
Closes astral-sh/ty#926