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Divide-and-conquer strategy for intersections of unions (#57871)

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This commit is contained in:
Anders Hejlsberg
2024-03-21 10:18:50 -07:00
committed by GitHub
parent 03c4b35255
commit ecb6eb2354
7 changed files with 720 additions and 2 deletions
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8
src/compiler/checker.ts
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@@ -17763,6 +17763,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
removeFromEach(typeSet, TypeFlags.Null);
result = getUnionType([getIntersectionType(typeSet), nullType], UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
}
else if (typeSet.length >= 4) {
// When we have four or more constituents, some of which are unions, we employ a "divide and conquer" strategy
// where A & B & C & D is processed as (A & B) & (C & D). Since intersections of unions often produce far smaller
// unions of intersections than the full cartesian product (due to some intersections becoming `never`), this can
// dramatically reduce the overall work.
const middle = Math.floor(typeSet.length / 2);
result = getIntersectionType([getIntersectionType(typeSet.slice(0, middle)), getIntersectionType(typeSet.slice(middle))], aliasSymbol, aliasTypeArguments);
}
else {
// We are attempting to construct a type of the form X & (A | B) & (C | D). Transform this into a type of
// the form X & A & C | X & A & D | X & B & C | X & B & D. If the estimated size of the resulting union type