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Perform structural inference for type parameters that are awaited

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This commit is contained in:
Anders Hejlsberg
2020-03-24 15:56:00 -07:00
parent cecab849db
commit d37484ee77
1 changed files with 10 additions and 6 deletions
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16
src/compiler/checker.ts
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@@ -18218,10 +18218,10 @@ namespace ts {
propagationType = savePropagationType;
return;
}
if (source.aliasSymbol && source.aliasTypeArguments && source.aliasSymbol === target.aliasSymbol) {
if (source.aliasSymbol && source.aliasTypeArguments && source.aliasSymbol === target.aliasSymbol &&
inferFromTypeArguments(source.aliasTypeArguments, target.aliasTypeArguments!, getAliasVariances(source.aliasSymbol))) {
// Source and target are types originating in the same generic type alias declaration.
// Simply infer from source type arguments to target type arguments.
inferFromTypeArguments(source.aliasTypeArguments, target.aliasTypeArguments!, getAliasVariances(source.aliasSymbol));
return;
}
if (source === target && source.flags & TypeFlags.UnionOrIntersection) {
@@ -18341,9 +18341,9 @@ namespace ts {
}
if (getObjectFlags(source) & ObjectFlags.Reference && getObjectFlags(target) & ObjectFlags.Reference && (
(<TypeReference>source).target === (<TypeReference>target).target || isArrayType(source) && isArrayType(target)) &&
!((<TypeReference>source).node && (<TypeReference>target).node)) {
!((<TypeReference>source).node && (<TypeReference>target).node) &&
inferFromTypeArguments(getTypeArguments(<TypeReference>source), getTypeArguments(<TypeReference>target), getVariances((<TypeReference>source).target))) {
// If source and target are references to the same generic type, infer from type arguments
inferFromTypeArguments(getTypeArguments(<TypeReference>source), getTypeArguments(<TypeReference>target), getVariances((<TypeReference>source).target));
}
else if (source.flags & TypeFlags.Index && target.flags & TypeFlags.Index) {
contravariant = !contravariant;
@@ -18463,6 +18463,9 @@ namespace ts {
}
function inferFromTypeArguments(sourceTypes: readonly Type[], targetTypes: readonly Type[], variances: readonly VarianceFlags[]) {
if (some(variances, variance => !!(variance & VarianceFlags.Awaited))) {
return false;
}
const count = sourceTypes.length < targetTypes.length ? sourceTypes.length : targetTypes.length;
for (let i = 0; i < count; i++) {
if (i < variances.length && (variances[i] & VarianceFlags.VarianceMask) === VarianceFlags.Contravariant) {
@@ -18475,6 +18478,7 @@ namespace ts {
inferFromTypes(sourceTypes[i], targetTypes[i]);
}
}
return true;
}
function inferFromContravariantTypes(source: Type, target: Type) {
@@ -18680,9 +18684,9 @@ namespace ts {
function inferFromObjectTypesWorker(source: Type, target: Type) {
if (getObjectFlags(source) & ObjectFlags.Reference && getObjectFlags(target) & ObjectFlags.Reference && (
(<TypeReference>source).target === (<TypeReference>target).target || isArrayType(source) && isArrayType(target))) {
(<TypeReference>source).target === (<TypeReference>target).target || isArrayType(source) && isArrayType(target)) &&
inferFromTypeArguments(getTypeArguments(<TypeReference>source), getTypeArguments(<TypeReference>target), getVariances((<TypeReference>source).target))) {
// If source and target are references to the same generic type, infer from type arguments
inferFromTypeArguments(getTypeArguments(<TypeReference>source), getTypeArguments(<TypeReference>target), getVariances((<TypeReference>source).target));
return;
}
if (isGenericMappedType(source) && isGenericMappedType(target)) {