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Allow callbacks unioned with null and/or undefined

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This commit is contained in:
Anders Hejlsberg
2017-04-10 17:14:11 -10:00
parent 510bc81967
commit ec35b800e3
1 changed files with 5 additions and 3 deletions
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8
src/compiler/checker.ts
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@@ -8213,8 +8213,8 @@ namespace ts {
for (let i = 0; i < checkCount; i++) {
const sourceType = i < sourceMax ? getTypeOfParameter(sourceParams[i]) : getRestTypeOfSignature(source);
const targetType = i < targetMax ? getTypeOfParameter(targetParams[i]) : getRestTypeOfSignature(target);
const sourceSig = getSingleCallSignature(sourceType);
const targetSig = getSingleCallSignature(targetType);
const sourceSig = getSingleCallSignature(getNonNullableType(sourceType));
const targetSig = getSingleCallSignature(getNonNullableType(targetType));
// In order to ensure that any generic type Foo<T> is at least co-variant with respect to T no matter
// how Foo uses T, we need to relate parameters bi-variantly (given that parameters are input positions,
// they naturally relate only contra-variantly). However, if the source and target parameters both have
@@ -8223,7 +8223,9 @@ namespace ts {
// similar to return values, callback parameters are output positions. This means that a Promise<T>,
// where T is used only in callback parameter positions, will be co-variant (as opposed to bi-variant)
// with respect to T.
const related = sourceSig && targetSig && !sourceSig.typePredicate && !targetSig.typePredicate ?
const callbacks = sourceSig && targetSig && !sourceSig.typePredicate && !targetSig.typePredicate &&
(getFalsyFlags(sourceType) & TypeFlags.Nullable) === (getFalsyFlags(targetType) & TypeFlags.Nullable);
const related = callbacks ?
compareSignaturesRelated(targetSig, sourceSig, /*checkAsCallback*/ true, /*ignoreReturnTypes*/ false, reportErrors, errorReporter, compareTypes) :
!checkAsCallback && compareTypes(sourceType, targetType, /*reportErrors*/ false) || compareTypes(targetType, sourceType, reportErrors);
if (!related) {