[red-knot] Understanding type[Union[A, B]]

[InSyncWithFoo]

Summary

Resolves #14834.

Test Plan

Markdown tests.

[InSyncWithFoo]

The failing test boils down to this:

import collections

MyObj1 = collections.namedtuple("MyObj1", ["a", "b"])

[MichaReiser]

The tests are failing with a panic in an assertion. Would you mind taking a look at what's happening

[AlexWaygood]

Thanks. There were a couple of issues with your initial patch; I've pushed to your branch to fix them:

• You didn't handle single-element unions such as type[Union[int]] (the subscript slice inside the Union[] is not an Expr::Tuple if there's only a single element).
• You were failing to store the types of subexpressions for subscripts that are either invalid or not-yet-supported; that was causing panics in the corpus test. It can be surprisingly tricky to make sure that you infer the type of each subexpression exactly once; it took me longer than I expected to fix this!
• Going forward, we'd prefer to use parameter annotations in mdtests to test type expressions rather than return annotations, as they're more concise ([red-knot] Improve the style of various mdtests #14839)

it doesn't panic anymore

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[InSyncWithFoo]

@AlexWaygood Thanks!