[ty] Implicit type aliases: Add support for typing.Union#21363
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Diagnostic diff on typing conformance testsChanges were detected when running ty on typing conformance tests--- old-output.txt 2025-11-12 11:47:18.914860495 +0000
+++ new-output.txt 2025-11-12 11:47:22.351880046 +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(19385)): 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(19b85)): 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__`
@@ -6,7 +6,6 @@
_directives_deprecated_library.py:45:24: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
aliases_explicit.py:41:24: error[invalid-type-form] List literals are not allowed in this context in a type expression: Did you mean `tuple[str, str]`?
aliases_explicit.py:45:10: error[invalid-type-form] Variable of type `Literal["int | str"]` is not allowed in a type expression
-aliases_explicit.py:49:5: error[type-assertion-failure] Argument does not have asserted type `int | str`
aliases_explicit.py:52:5: error[type-assertion-failure] Argument does not have asserted type `list[int]`
aliases_explicit.py:53:5: error[type-assertion-failure] Argument does not have asserted type `tuple[str, ...] | list[str]`
aliases_explicit.py:54:5: error[type-assertion-failure] Argument does not have asserted type `tuple[int, int, int, str]`
@@ -18,7 +17,6 @@
aliases_explicit.py:61:5: error[type-assertion-failure] Argument does not have asserted type `int | str`
aliases_explicit.py:101:6: error[call-non-callable] Object of type `UnionType` is not callable
aliases_implicit.py:54:24: error[invalid-type-form] List literals are not allowed in this context in a type expression: Did you mean `tuple[str, str]`?
-aliases_implicit.py:60:5: error[type-assertion-failure] Argument does not have asserted type `int | str`
aliases_implicit.py:63:5: error[type-assertion-failure] Argument does not have asserted type `list[int]`
aliases_implicit.py:64:5: error[type-assertion-failure] Argument does not have asserted type `tuple[str, ...] | list[str]`
aliases_implicit.py:65:5: error[type-assertion-failure] Argument does not have asserted type `tuple[int, int, int, str]`
@@ -1003,5 +1001,5 @@
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 1005 diagnostics
+Found 1003 diagnostics
WARN A fatal error occurred while checking some files. Not all project files were analyzed. See the diagnostics list above for details.
|
|
| Lint rule | Added | Removed | Changed |
|---|---|---|---|
invalid-key |
2,160 | 0 | 0 |
unused-ignore-comment |
7 | 443 | 0 |
invalid-argument-type |
264 | 5 | 116 |
invalid-assignment |
134 | 12 | 13 |
possibly-missing-attribute |
98 | 8 | 4 |
no-matching-overload |
78 | 0 | 0 |
non-subscriptable |
24 | 18 | 20 |
invalid-return-type |
32 | 5 | 7 |
unresolved-attribute |
40 | 1 | 2 |
invalid-type-form |
24 | 0 | 0 |
unsupported-operator |
12 | 1 | 7 |
call-non-callable |
18 | 1 | 0 |
possibly-missing-implicit-call |
3 | 0 | 10 |
invalid-context-manager |
0 | 0 | 10 |
not-iterable |
7 | 0 | 2 |
invalid-parameter-default |
5 | 0 | 0 |
too-many-positional-arguments |
4 | 0 | 0 |
redundant-cast |
2 | 0 | 0 |
deprecated |
0 | 1 | 0 |
index-out-of-bounds |
1 | 0 | 0 |
possibly-unresolved-reference |
0 | 1 | 0 |
type-assertion-failure |
0 | 1 | 0 |
| Total | 2,913 | 497 | 191 |
CodSpeed Performance ReportMerging #21363 will degrade performances by 91.64%Comparing Summary
Benchmarks breakdown
Footnotes
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carljm
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Nice! Personally I think we can land this even with the big perf regression on pydantic, especially if that regression still leaves us on par with pyrefly. But of course if we can optimize, that's better!
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| An empty `typing.Union` leads to a `TypeError` at runtime, so we emit an error. We still infer | ||
| `Never` when used as a type expression, which seems reasonable for an empty union: |
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👍 I don't know why this raises an error at runtime, seems silly to me.
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Summary
Add support for
typing.Unionin implicit type aliases / in value position.Typing conformance tests
Two new tests are passing
Ecosystem impact
invalid-keydiagnostics on pydantic are caused by Implement "tagged union" narrowing for namedtuples and arbitrary nominal types ty#1479 (comment).Test Plan
New Markdown tests