[ty] implement typing.NewType as Type::NewTypeInstance
#21157
+1,154
−186
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Diagnostic diff on typing conformance testsChanges were detected when running ty on typing conformance tests--- old-output.txt 2025-11-06 22:46:32.505249634 +0000
+++ new-output.txt 2025-11-06 22:46:35.797264599 +0000
@@ -1,4 +1,4 @@
-fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/05a9af7/src/function/execute.rs:451:17 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(18b71)): execute: too many cycle iterations`
+fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/05a9af7/src/function/execute.rs:451:17 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(18f71)): execute: too many cycle iterations`
_directives_deprecated_library.py:15:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `int`
_directives_deprecated_library.py:30:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
_directives_deprecated_library.py:36:41: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Self@__add__`
@@ -41,11 +41,19 @@
aliases_implicit.py:119:10: error[invalid-type-form] Variable of type `Literal["int | str"]` is not allowed in a type expression
aliases_implicit.py:128:1: error[type-assertion-failure] Argument does not have asserted type `list[str]`
aliases_implicit.py:133:6: error[call-non-callable] Object of type `UnionType` is not callable
-aliases_newtype.py:15:1: error[type-assertion-failure] Argument does not have asserted type `int`
-aliases_newtype.py:18:1: error[invalid-assignment] Object of type `NewType` is not assignable to `type`
-aliases_newtype.py:23:16: error[invalid-argument-type] Argument to function `isinstance` is incorrect: Expected `type | UnionType | tuple[Unknown, ...]`, found `NewType`
-aliases_newtype.py:26:21: error[invalid-base] Invalid class base with type `NewType`
-aliases_newtype.py:63:43: error[too-many-positional-arguments] Too many positional arguments to bound method `__init__`: expected 3, got 4
+aliases_newtype.py:11:8: error[invalid-argument-type] Argument is incorrect: Expected `int`, found `Literal["user"]`
+aliases_newtype.py:12:1: error[invalid-assignment] Object of type `Literal[42]` is not assignable to `UserId`
+aliases_newtype.py:18:1: error[invalid-assignment] Object of type `<NewType pseudo-class 'UserId'>` is not assignable to `type`
+aliases_newtype.py:23:16: error[invalid-argument-type] Argument to function `isinstance` is incorrect: Expected `type | UnionType | tuple[Unknown, ...]`, found `<NewType pseudo-class 'UserId'>`
+aliases_newtype.py:26:21: error[invalid-base] Cannot subclass an instance of NewType
+aliases_newtype.py:35:1: error[invalid-newtype] The name of a `NewType` (`BadName`) must match the name of the variable it is assigned to (`GoodName`)
+aliases_newtype.py:41:6: error[invalid-type-form] `GoodNewType1` is a `NewType` and cannot be specialized
+aliases_newtype.py:47:38: error[invalid-newtype] invalid base for `typing.NewType`: type `int | str`
+aliases_newtype.py:52:38: error[invalid-newtype] invalid base for `typing.NewType`: type `Hashable`
+aliases_newtype.py:54:38: error[invalid-newtype] invalid base for `typing.NewType`: type `Literal[7]`
+aliases_newtype.py:61:38: error[invalid-newtype] invalid base for `typing.NewType`: type `TD1`
+aliases_newtype.py:63:15: error[invalid-newtype] Wrong number of arguments in `NewType` creation, expected 2, found 3
+aliases_newtype.py:65:38: error[invalid-newtype] invalid base for `typing.NewType`: type `Any`
aliases_type_statement.py:10:19: error[too-many-positional-arguments] Too many positional arguments: expected 1, got 3
aliases_type_statement.py:17:1: error[unresolved-attribute] Object of type `typing.TypeAliasType` has no attribute `bit_count`
aliases_type_statement.py:19:1: error[call-non-callable] Object of type `TypeAliasType` is not callable
@@ -587,7 +595,7 @@
generics_typevartuple_basic.py:12:14: error[invalid-argument-type] `@Todo(starred expression)` is not a valid argument to `Generic`
generics_typevartuple_basic.py:16:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `tuple[@Todo(PEP 646), ...]`
generics_typevartuple_basic.py:23:13: error[invalid-argument-type] `@Todo(starred expression)` is not a valid argument to `Generic`
-generics_typevartuple_basic.py:42:34: error[invalid-argument-type] Argument to bound method `__init__` is incorrect: Expected `tuple[@Todo(PEP 646), ...]`, found `Literal[1]`
+generics_typevartuple_basic.py:42:34: error[invalid-argument-type] Argument to bound method `__init__` is incorrect: Expected `tuple[@Todo(PEP 646), ...]`, found `Height`
generics_typevartuple_basic.py:65:27: error[unknown-argument] Argument `covariant` does not match any known parameter of function `__new__`
generics_typevartuple_basic.py:66:27: error[too-many-positional-arguments] Too many positional arguments to function `__new__`: expected 2, got 4
generics_typevartuple_basic.py:67:27: error[unknown-argument] Argument `bound` does not match any known parameter of function `__new__`
@@ -1002,5 +1010,5 @@
typeddicts_usage.py:28:17: error[missing-typed-dict-key] Missing required key 'name' in TypedDict `Movie` constructor
typeddicts_usage.py:28:18: error[invalid-key] Invalid key for TypedDict `Movie`: Unknown key "title"
typeddicts_usage.py:40:24: error[invalid-type-form] The special form `typing.TypedDict` is not allowed in type expressions. Did you mean to use a concrete TypedDict or `collections.abc.Mapping[str, object]` instead?
-Found 1004 diagnostics
+Found 1012 diagnostics
WARN A fatal error occurred while checking some files. Not all project files were analyzed. See the diagnostics list above for details. |
AlexWaygood
changed the title
typing.NewType as Type::NewTypeInstancetyping.NewType as Type::NewTypeInstance
oconnor663
commented
Oct 31, 2025
|
| Lint rule | Added | Removed | Changed |
|---|---|---|---|
invalid-argument-type |
495 | 1 | 3 |
unused-ignore-comment |
0 | 39 | 0 |
unsupported-operator |
5 | 0 | 4 |
invalid-assignment |
4 | 1 | 0 |
invalid-return-type |
2 | 1 | 2 |
type-assertion-failure |
2 | 0 | 2 |
invalid-newtype |
2 | 0 | 0 |
no-matching-overload |
2 | 0 | 0 |
call-non-callable |
0 | 0 | 1 |
non-subscriptable |
1 | 0 | 0 |
unresolved-attribute |
0 | 0 | 1 |
| Total | 513 | 42 | 13 |
This comment was marked as resolved.
This comment was marked as resolved.
AlexWaygood
reviewed
Oct 31, 2025
oconnor663
force-pushed
the
jack/newtype4
branch
from
611cbb3 to
893a2a5
Compare
|
|
Relevant to the error formatting tweak I just pushed in daeb800, do we like the example in that commit message: from typing import NewType
from nonexistent_module import Foo
Bar = NewType("Bar", Foo)That's a result of the check that says a |
Nice, these changes all look like true positives -- places where we should have been emitting diagnostics, but we previously weren't! |
I think it would be good to suppress the diagnostic here if the second argument has a dynamic type. The user will get a diagnostic from the unresolved import in your example; there's not much use in having cascading diagnostics later on in the module due to the same issue. |
AlexWaygood
reviewed
Nov 2, 2025
There was a problem hiding this comment.
Here's my full review. Overall this looks excellent!! This definitely looks like right overall approach IMO.
My main feedback is that it would be great to have some more tests for various parts of the behaviour that you're implementing here. I left some comments inline about things that look correct, but that it would be great to explicitly test. It might also be worth looking through the typing conformance-suite tests for newtype, and/or mypy's tests for newtype, to see if there are any other things that would be worth testing for explicitly.
Comment on lines
+5227
to
+5292
| Some(KnownClass::NewType) => { | ||
| Binding::single( | ||
| self, | ||
| Signature::new( | ||
| Parameters::new([ | ||
| Parameter::positional_or_keyword(Name::new_static("name")) | ||
| .with_annotated_type(Type::LiteralString), | ||
| Parameter::positional_or_keyword(Name::new_static("tp")), | ||
| ]), | ||
| // The actual return type is a KnownInstanceType::NewType(_), but each | ||
| // callsite gets a unique payload, including a `Definition` that points | ||
| // to that callsite. See `struct NewType` and `infer_newtype_expression`. | ||
| None, | ||
| ), | ||
| ) | ||
| .into() | ||
| } |
There was a problem hiding this comment.
one issue here is that on Python 3.9, NewType is a function rather than a class. I don't know if this really matters this much TBH, since Python 3.9 is now end-of-life, and supporting both the pre-3.9 version of NewType (where it was a function) and the 3.10-version of NewType (where it's a class) is going to lead to complications for us.
At the very least, it might be good to add an mdtest with python-version = "3.9" so that we document that we don't support NewType on Python <=3.9 currently. But I would certainly be inclined to leave <=3.9 support out of the first PR adding support for NewType.
There was a problem hiding this comment.
What's your recommendation for this diagnostic? It doesn't look like I have an InferContext at this point to directly emit something. Is there a type that I can return that indirectly forces a diagnostic? (edit: ah you're not asking for a diagnostic)
oconnor663
force-pushed
the
jack/newtype4
branch
from
daeb800 to
7d3cec6
Compare
AlexWaygood
reviewed
Nov 6, 2025
oconnor663
force-pushed
the
jack/newtype4
branch
from
c6b8501 to
94cec7a
Compare
oconnor663
commented
Nov 6, 2025
| .and_then(|cls| cls.known(self.db())); | ||
| if let Some(KnownClass::NewType) = known_class { | ||
| self.infer_newtype_assignment_deferred(arguments); | ||
| return; |
There was a problem hiding this comment.
I just pushed a big rebase (addressing most of @AlexWaygood's comments, but now I see there are more :-D ), and this part ended up being tricky. It looks like if I don't short-circuit here, I run into a panic about inferring the same expression (the second arg) twice. Please let me know if this looks like the right way to avoid that, and whether it's maybe worthy of a block comment saying why this is sensitive?
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
astral-sh/ty#742. This PR rewrites and supersedes my previous
NewTypePR, #20126. The high-level changes:Type::NewTypeInstanceinstead of expandingNominalInstanceInner.infer_legacy_typevarinTypeInferenceBuilder::infer_assignment_definition_impl.There are severalI've moved this out of Draft.// REVIEWERS:questions inline, and I expect I've gone about some things the wrong way (particularly cycle detection?), so I'm leaving this in Draft status for now.