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Add heuristic for extracting irreducible null and undefined types from intersections of unions (#33150)

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This commit is contained in:
Wesley Wigham
2019-09-06 11:32:22 -07:00
committed by GitHub
parent c26c44d5fc
commit a93298665c
5 changed files with 677 additions and 0 deletions
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16
src/compiler/checker.ts
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@@ -9996,6 +9996,16 @@ namespace ts {
return true;
}
function extractIrreducible(types: Type[], flag: TypeFlags) {
if (every(types, t => !!(t.flags & TypeFlags.Union) && some((t as UnionType).types, tt => !!(tt.flags & flag)))) {
for (let i = 0; i < types.length; i++) {
types[i] = filterType(types[i], t => !(t.flags & flag));
}
return true;
}
return false;
}
// If the given list of types contains more than one union of primitive types, replace the
// first with a union containing an intersection of those primitive types, then remove the
// other unions and return true. Otherwise, do nothing and return false.
@@ -10114,6 +10124,12 @@ namespace ts {
// reduced we'll never reduce again, so this occurs at most once.
result = getIntersectionType(typeSet, aliasSymbol, aliasTypeArguments);
}
else if (extractIrreducible(typeSet, TypeFlags.Undefined)) {
result = getUnionType([getIntersectionType(typeSet), undefinedType], UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
}
else if (extractIrreducible(typeSet, TypeFlags.Null)) {
result = getUnionType([getIntersectionType(typeSet), nullType], UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
}
else {
// We are attempting to construct a type of the form X & (A | B) & Y. Transform this into a type of
// the form X & A & Y | X & B & Y and recursively reduce until no union type constituents remain.