Optimize creation of intersections of union types #25859
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src/compiler/checker.ts
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| // Remove all unions of primitive types from the given list and replace them with a | ||
| // single union containing an intersection of those primitive types. | ||
| function intersectUnionsOfPrimitiveTypes(types: Type[]) { |
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When does this return true/false? Can you make this explicit?
| function eachUnionContains(unionTypes: UnionType[], type: Type) { | ||
| for (const u of unionTypes) { | ||
| if (!containsType(u.types, type)) { | ||
| const primitive = type.flags & TypeFlags.StringLiteral ? stringType : |
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This logic is very close to getBaseTypeOfLiteralType; can you use that instead? That also covers enums, though it won't come into play for the motivating issue.
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Although a 200 member enum could easily cause the same issues, so is probably worth covering!
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No, we can't use that instead because it maps an enum literal type to its defining union type (the union of all enum literal types in the same enum type declaration) which we don't want here. We only want to handle the special "infinite sets" denoted by string, number, and symbol.
| const result: Type[] = []; | ||
| for (const u of unionTypes) { | ||
| for (const t of u.types) { | ||
| if (insertType(checked, t)) { |
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In the worst-case, this can force checked to reallocate or bulk-move all the elements a lot. Do we believe that won't be an issue?
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We could potentially use a Map but that's going to allocate more memory and go slower in the typical cases (i.e. reasonably sized sets of types with a high degree of similarity). I'm not too concerned with it.
This PR optimizes creation of intersections of union types containing both unit types (such as string and numeric literal types) and primitive types (such as
stringandnumber). This fixes the severe performance issues we have whenkeyofis applied to large unions of object types that have string and/or numeric index signatures. (Given a union typeUwith constituentsT0 | T1 | ... | Tn, we rewritekeyof Utokeyof T0 & keyof T1 & ... & keyof Tn. Thus it is important to have efficient resolution of such types.)Fixes #24223.