[red-knot] add IntersectionBuilder #12791
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AlexWaygood
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Aug 10, 2024
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(Have only skimmed so far; will look in more depth over the weekend or next week :-) |
AlexWaygood
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Aug 10, 2024
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Thanks for the great review! |
CodSpeed Performance ReportMerging #12791 will not alter performanceComparing Summary
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AlexWaygood
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MichaReiser
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Aug 12, 2024
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For type narrowing, we'll need intersections (since applying type narrowing is just a type intersection.)
Add
IntersectionBuilder, along with some tests for it andUnionBuilder(renamed fromUnionTypeBuilder).We use smart builders to ensure that we always keep these types in disjunctive normal form (DNF). That means that we never have deeply nested trees of unions and intersections: unions flatten into unions, intersections flatten into intersections, and intersections distribute over unions, so the most complex tree we can ever have is a union of intersections. We also never have a single-element union or a single-positive-element intersection; these both just simplify to the contained type.
Maintaining these invariants means that
UnionBuilderdoesn't necessarily end up building aType::Union(e.g. if you only add a single type to the union, it'll just return that type instead), andIntersectionBuilderdoesn't necessarily build aType::Intersection(if you add a union to the intersection, we distribute the intersection over that union, andIntersectionBuilderwill end up returning aType::Unionof intersections).We also simplify intersections by ensuring that if a type and its negation are both in an intersection, they simplify out. (In future this should also respect subtyping, not just type identity, but we don't have subtyping yet.) We do implement subtyping of
Neveras a special case for now.Most of this PR is unused for now until type narrowing lands; I'm just breaking it out to reduce the review fatigue of a single massive PR.