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[ty] Reachability and narrowing for enum methods#21130

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sharkdp merged 1 commit intomainfrom
david/narrowing-for-enum-methods
Oct 30, 2025
Merged

[ty] Reachability and narrowing for enum methods#21130
sharkdp merged 1 commit intomainfrom
david/narrowing-for-enum-methods

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@sharkdp sharkdp commented Oct 29, 2025 •
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Summary

Adds proper type narrowing and reachability analysis for matching on non-inferable type variables bound to enums. For example:

from enum import Enum

class Answer(Enum):
    NO = 0
    YES = 1

    def is_yes(self) -> bool:  # no error here!
        match self:
            case Answer.YES:
                return True
            case Answer.NO:
                return False

closes astral-sh/ty#1404

Test Plan

Added regression tests

@sharkdp sharkdp added ty Multi-file analysis & type inference ecosystem-analyzer labels Oct 29, 2025
@sharkdp sharkdp force-pushed the david/narrowing-for-enum-methods branch from 4d39b75 to 2946e79 Compare October 29, 2025 20:30
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github-actions bot commented Oct 29, 2025 •
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Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

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github-actions bot commented Oct 29, 2025 •
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mypy_primer results

Changes were detected when running on open source projects 
mitmproxy (https://github.com/mitmproxy/mitmproxy)
- mitmproxy/proxy/layers/http/_events.py:127:17: error[type-assertion-failure] Argument does not have asserted type `Never`
- Found 1890 diagnostics
+ Found 1889 diagnostics

jax (https://github.com/google/jax)
- jax/_src/pallas/mosaic_gpu/core.py:1527:24: error[invalid-return-type] Function can implicitly return `None`, which is not assignable to return type `TMEMLayout`
- Found 2545 diagnostics
+ Found 2544 diagnostics
No memory usage changes detected ✅

@sharkdp sharkdp force-pushed the david/narrowing-for-enum-methods branch from 2946e79 to 6a9bc2e Compare October 30, 2025 13:15
@sharkdp sharkdp marked this pull request as ready for review October 30, 2025 13:19
AlexWaygood
AlexWaygood reviewed Oct 30, 2025
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github-actions bot commented Oct 30, 2025

ecosystem-analyzer results

Lint rule Added Removed Changed
invalid-return-type 0 1 0
type-assertion-failure 0 1 0
Total 0 2 0

Full report with detailed diff (timing results)

@sharkdp sharkdp force-pushed the david/narrowing-for-enum-methods branch from 6a9bc2e to 236427f Compare October 30, 2025 13:36
AlexWaygood
AlexWaygood reviewed Oct 30, 2025
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AlexWaygood
AlexWaygood reviewed Oct 30, 2025
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AlexWaygood
AlexWaygood reviewed Oct 30, 2025
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This fixes the issue for methods on enums, but there appear to be lots of other cases where you can have a TypeVar bound to a union (or type equivalent to a union) where we also exhibit similar issues with reachability and narrowing. These are all on this branch:

from typing import assert_never, Literal

def f[T: bool](x: T) -> T:
    match x:
        case True:
            return x
        case False:
            return x
        case _:
            reveal_type(x) # T@f & ~Literal[True] & ~Literal[False]
            assert_never(x)  # false-positive error

def g[T: Literal["foo", "bar"]](x: T) -> T:
    match x:
        case "foo":
            return x
        case "bar":
            return x
        case _:
            reveal_type(x)  # T@g & ~Literal["foo"] & ~Literal["bar"]
            assert_never(x)  # false-positive error

def h[T: int | str](x: T) -> T:
    if isinstance(x, int):
        return x
    elif isinstance(x, str):
        return x
    else:
        reveal_type(x)  # T@h & ~int & ~str
        assert_never(x)  # false-positive error

@sharkdp sharkdp force-pushed the david/narrowing-for-enum-methods branch from 236427f to 53b79d8 Compare October 30, 2025 14:16
@sharkdp sharkdp mentioned this pull request Oct 30, 2025
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@sharkdp sharkdp merged commit e55bc94 into main Oct 30, 2025
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@sharkdp sharkdp deleted the david/narrowing-for-enum-methods branch October 30, 2025 14:38
dcreager added a commit that referenced this pull request Oct 30, 2025
@dcreager
Merge remote-tracking branch 'origin/main' into dcreager/satisfies
c8135c5 
* origin/main: (21 commits)
  [ty] Update "constraint implication" relation to work on constraints between two typevars (#21068)
  [`flake8-type-checking`] Fix `TC003` false positive with `future-annotations` (#21125)
  [ty] Fix lookup of `__new__` on instances (#21147)
  Fix syntax error false positive on nested alternative patterns (#21104)
  [`pyupgrade`] Fix false positive for `TypeVar` with default on Python <3.13 (`UP046`,`UP047`) (#21045)
  [ty] Reachability and narrowing for enum methods (#21130)
  [ty] Use `range` instead of custom `IntIterable` (#21138)
  [`ruff`] Add support for additional eager conversion patterns (`RUF065`) (#20657)
  [`ruff-ecosystem`] Fix CLI crash on Python 3.14 (#21092)
  [ty] Infer type of `self` for decorated methods and properties (#21123)
  [`flake8-bandit`] Fix correct example for `S308` (#21128)
  [ty] Dont provide goto definition for definitions which are not reexported in builtins (#21127)
  [`airflow`] warning `airflow....DAG.create_dagrun` has been removed (`AIR301`) (#21093)
  [ty] follow the breaking API changes made in salsa-rs/salsa#1015 (#21117)
  [ty] Rename `Type::into_nominal_instance` (#21124)
  [ty] Filter out "unimported" from the current module
  [ty] Add evaluation test for auto-import including symbols in current module
  [ty] Refactor `ty_ide` completion tests
  [ty] Render `import <...>` in completions when "label details" isn't supported
  [`refurb`] Preserve digit separators in `Decimal` constructor (`FURB157`) (#20588)
  ...
@AlexWaygood AlexWaygood mentioned this pull request Oct 31, 2025
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@AlexWaygood AlexWaygood AlexWaygood approved these changes

@carljm carljm Awaiting requested review from carljm carljm is a code owner

@dcreager dcreager Awaiting requested review from dcreager dcreager is a code owner

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Failed exhaustiveness matching on type variable

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