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Eliminate intersections of unit types in union types

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This commit is contained in:
Anders Hejlsberg 2017-09-07 16:02:00 -07:00
parent 8d1eb29fb1
commit 4885560cb4
1 changed files with 5 additions and 1 deletions
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6
src/compiler/checker.ts
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@ -7302,7 +7302,11 @@ namespace ts {
if (flags & TypeFlags.Null) typeSet.containsNull = true;
if (!(flags & TypeFlags.ContainsWideningType)) typeSet.containsNonWideningType = true;
}
else if (!(flags & TypeFlags.Never)) {
else if (!(flags & TypeFlags.Never || flags & TypeFlags.Intersection && every((<IntersectionType>type).types, isUnitType))) {
// We ignore 'never' types in unions. Likewise, we ignore intersections of unit types as they are
// another form of 'never' (in that they have an empty value domain). We could in theory turn
// intersections of unit types into 'never' upon construction, but deferring the reduction makes it
// easier to reason about their origin.
if (flags & TypeFlags.String) typeSet.containsString = true;
if (flags & TypeFlags.Number) typeSet.containsNumber = true;
if (flags & TypeFlags.StringOrNumberLiteral) typeSet.containsStringOrNumberLiteral = true;