Codestin Search App

charliermarsh · 2026-06-13T02:54:46Z

Summary

We already infer the types of captures and aliases in sequence patterns by following the values passed from each pattern node to its children. This PR extends the same recursive analysis to class and mapping patterns.

from dataclasses import dataclass
from typing import Literal, TypedDict

class IntPayload(TypedDict):
    tag: Literal["int"]
    value: int

class StrPayload(TypedDict):
    tag: Literal["str"]
    value: str

@dataclass
class Box:
    payload: IntPayload | StrPayload

def handle(box: Box) -> None:
    match box:
        case Box({"tag": "int", "value": value}) as whole:
            reveal_type(value)  # int
            reveal_type(whole)  # Box

A class pattern passes the selected instance member to each child pattern. Positional patterns resolve that member through __match_args__; keyword patterns use the named attribute. A mapping pattern passes the value associated with each matched key, while **rest receives the new dictionary built from the remaining entries.

astral-sh-bot · 2026-06-13T02:56:26Z

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 94.47%. The percentage of expected errors that received a diagnostic held steady at 89.19%. The number of fully passing files held steady at 95/134.

astral-sh-bot · 2026-06-13T02:57:12Z

Memory usage report

Memory usage unchanged ✅

astral-sh-bot · 2026-06-13T02:59:18Z

`ecosystem-analyzer` results

Lint rule	Added	Removed	Changed
`unresolved-attribute`	8	0	0
`invalid-argument-type`	6	0	0
`invalid-assignment`	0	0	3
`type-assertion-failure`	0	1	2
`invalid-return-type`	1	1	0
`no-matching-overload`	1	0	0
Total	16	2	5

Flaky changes detected. This PR summary excludes flaky changes; see the HTML report for details.

Raw diff (23 changes)

cwltool (https://github.com/common-workflow-language/cwltool)
+ cwltool/main.py:244:57 error[no-matching-overload] No overload of bound method `str.join` matches arguments
+ cwltool/validate_js.py:101:29 error[invalid-argument-type] Method `__getitem__` of type `bound method Top[MutableMapping[Unknown, Unknown]].__getitem__(key: Never, /) -> object` cannot be called with key of type `str` on object of type `Top[MutableMapping[Unknown, Unknown]]`
+ cwltool/validate_js.py:101:29 error[invalid-argument-type] Method `__getitem__` of type `bound method str.__getitem__(key: SupportsIndex | slice[SupportsIndex | None, SupportsIndex | None, SupportsIndex | None], /) -> str` cannot be called with key of type `str` on object of type `str`

egglog-python (https://github.com/egraphs-good/egglog-python)
- python/egglog/egraph_state.py:378:25 error[type-assertion-failure] Type `Unknown & ~Literal["delete"] & ~Literal["subsume"]` is not equivalent to `Never`
- python/egglog/egraph_state.py:623:25 error[type-assertion-failure] Type `Unknown & ~None` is not equivalent to `Never`
+ python/egglog/egraph_state.py:623:25 error[type-assertion-failure] Type `Value` is not equivalent to `Never`
- python/egglog/pretty.py:309:17 error[type-assertion-failure] Type `Unknown & ~None` is not equivalent to `Never`
+ python/egglog/pretty.py:309:17 error[type-assertion-failure] Type `Value` is not equivalent to `Never`
+ python/egglog/thunk.py:69:28 error[invalid-return-type] Return type does not match returned value: expected `T@__call__`, found `TypeVar`

jax (https://github.com/google/jax)
- jax/experimental/mosaic/gpu/constraints.py:211:6 error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `Variable | RegisterLayout | TMEMLayout | ... omitted 6 union elements`

pylint (https://github.com/pycqa/pylint)
+ pylint/checkers/match_statements_checker.py:164:25 error[unresolved-attribute] Attribute `value` is not defined on `NodeNG` in union `NodeNG | Proxy`
+ pylint/checkers/classes/class_checker.py:946:54 error[unresolved-attribute] Attribute `name` is not defined on `NodeNG` in union `NodeNG | UninferableBase | Proxy`
+ pylint/checkers/refactoring/recommendation_checker.py:261:29 error[unresolved-attribute] Attribute `name` is not defined on `Attribute` in union `Attribute | Name`
+ pylint/checkers/refactoring/recommendation_checker.py:265:29 error[unresolved-attribute] Attribute `attrname` is not defined on `Name` in union `Attribute | Name`
+ pylint/checkers/refactoring/refactoring_checker.py:652:16 error[unresolved-attribute] Object of type `NodeNG | None` has no attribute `value`
+ pylint/checkers/refactoring/refactoring_checker.py:1178:12 error[unresolved-attribute] Object of type `NodeNG` has no attribute `name`
+ pylint/checkers/refactoring/refactoring_checker.py:1830:32 error[unresolved-attribute] Attribute `name` is not defined on `NodeNG` in union `NodeNG | Proxy`
+ pylint/checkers/refactoring/refactoring_checker.py:1841:38 error[unresolved-attribute] Attribute `name` is not defined on `NodeNG` in union `NodeNG | Proxy`
+ pylint/checkers/utils.py:1303:83 error[invalid-argument-type] Argument to function `has_known_bases` is incorrect: Expected `ClassDef`, found `(ClassDef & BaseInstance) | (FunctionDef & BaseInstance) | (Lambda & BaseInstance) | (UnboundMethod & BaseInstance)`
+ pylint/checkers/utils.py:1304:38 error[invalid-argument-type] Argument is incorrect: Expected `NodeNG`, found `(ClassDef & BaseInstance) | (FunctionDef & BaseInstance) | (Lambda & BaseInstance) | (UnboundMethod & BaseInstance)`

pytest (https://github.com/pytest-dev/pytest)
- src/_pytest/assertion/rewrite.py:1012:25 error[invalid-assignment] Invalid subscript assignment with key of type `Unknown` and value of type `expr` on object of type `dict[str, str]`
+ src/_pytest/assertion/rewrite.py:1012:25 error[invalid-assignment] Invalid subscript assignment with key of type `str` and value of type `expr` on object of type `dict[str, str]`
- src/_pytest/assertion/rewrite.py:1110:17 error[invalid-assignment] Invalid subscript assignment with key of type `Unknown` and value of type `NamedExpr` on object of type `dict[str, str]`
+ src/_pytest/assertion/rewrite.py:1110:17 error[invalid-assignment] Invalid subscript assignment with key of type `str` and value of type `NamedExpr` on object of type `dict[str, str]`
- src/_pytest/assertion/rewrite.py:1128:21 error[invalid-assignment] Invalid subscript assignment with key of type `Unknown` and value of type `NamedExpr` on object of type `dict[str, str]`
+ src/_pytest/assertion/rewrite.py:1128:21 error[invalid-assignment] Invalid subscript assignment with key of type `Any & str` and value of type `NamedExpr` on object of type `dict[str, str]`

schema_salad (https://github.com/common-workflow-language/schema_salad)
+ src/schema_salad/typescript_codegen.py:408:25 error[invalid-argument-type] Argument is incorrect: Expected `bool`, found `Any | str | Literal[False]`

typeshed-stats (https://github.com/AlexWaygood/typeshed-stats)
+ src/typeshed_stats/gather.py:520:27 error[invalid-argument-type] Argument to function `sorted` is incorrect: Expected `Iterable[str]`, found `Top[list[Unknown]]`

Full report with detailed diff (timing results)

codspeed-hq · 2026-06-15T01:32:25Z

Merging this PR will not alter performance

✅ 85 untouched benchmarks
⏩ 64 skipped benchmarks¹

_{Comparing charlie/class-mapping-pattern-bindings (17abf80) with main (71541d4)}

64 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

charliermarsh · 2026-06-26T00:05:21Z

+def test_widened_match_args_does_not_select_an_attribute(value: WidenedMatchArgs) -> None:
+    match value:
+        case WidenedMatchArgs(item):
+            reveal_type(item)  # revealed: Unknown


A bit questionable, but consistent, I think.

Consistent with other type checkers?

I agree here though.

dhruvmanila

Looks good!

dhruvmanila · 2026-06-26T09:25:25Z

+def test_match_nested_generic_subclass_capture(value: GenericPatternBase[int]) -> list[int]:
+    match value:
+        case GenericPatternChild(items=items):
+            reveal_type(items)  # revealed: Unknown


Should there be a TODO here given that this should be list[int] instead of Unknown?

dhruvmanila · 2026-06-26T09:32:26Z

+def test_widened_match_args_does_not_select_an_attribute(value: WidenedMatchArgs) -> None:
+    match value:
+        case WidenedMatchArgs(item):
+            reveal_type(item)  # revealed: Unknown


Consistent with other type checkers?

I agree here though.

dhruvmanila · 2026-06-26T09:40:21Z

+        case MissingClassPatternAttribute(missing=item) | (int() as item):
+            reveal_type(item)  # revealed: int


This is cool given that other type checkers reveal Unknown | int (or Any | int) which is incorrect (because of @final) given that the first pattern can never be matched here.

dhruvmanila · 2026-06-26T09:46:12Z

+def test_definite_class_alternative_removes_later_bindings(value: DefiniteFirst) -> None:
+    match value:
+        case (DefiniteFirst() as item) | UnreachableLater(payload=item):
+            reveal_type(item)  # revealed: DefiniteFirst


When I switch the order here as follows it reveals str | DefiniteFirst which I think is correct given that DefiniteFirst is not a final class in this example. Can we add both of these test cases here? One where the order is switched and the other which additionally also sets the DefiniteFirst as a final class?

def test_definite_class_alternative_removes_later_bindings(value: DefiniteFirst) -> None: match value: case UnreachableLater(payload=item) | (DefiniteFirst() as item): reveal_type(item) # revealed: str | DefiniteFirst

dhruvmanila · 2026-06-26T09:52:15Z

+class OverlapCaptureB:
+    member: int
+
+class OverlapCaptureC(OverlapCaptureA, OverlapCaptureB): ...


The OverlapCaptureC seems unused here?

charliermarsh added the ty Multi-file analysis & type inference label Jun 13, 2026

charliermarsh mentioned this pull request Jun 13, 2026

[ty] Infer class and mapping pattern bindings #25935

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charliermarsh mentioned this pull request Jun 13, 2026

[ty] Narrow match subjects through structural patterns #25942

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charliermarsh mentioned this pull request Jun 15, 2026

[ty] Infer types for names bound in sequence match patterns #25940

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charliermarsh changed the base branch from charlie/pattern-as to charlie/class-pattern-exhaustiveness June 15, 2026 14:48

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charliermarsh commented Jun 26, 2026

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dhruvmanila approved these changes Jun 26, 2026

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charliermarsh added 3 commits June 26, 2026 06:38

[ty] Infer class and mapping pattern bindings

b1f1995

[ty] Clarify class pattern binding documentation

dff176a

[ty] Address class pattern review feedback

17abf80

charliermarsh mentioned this pull request Jun 26, 2026

[ty] Fix structural pattern binding inference #26411

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[ty] Infer class and mapping pattern bindings#25941

[ty] Infer class and mapping pattern bindings#25941
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		case MissingClassPatternAttribute(missing=item) \| (int() as item):
		reveal_type(item) # revealed: int

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Merging this PR will not alter performance

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