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Propagate 'never' and the wildcard type in type inference

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This commit is contained in:
Anders Hejlsberg
2018-02-27 15:10:43 -08:00
parent b9e06bfd38
commit de3871a4fc
2 changed files with 21 additions and 7 deletions
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25
src/compiler/checker.ts
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@@ -11496,8 +11496,15 @@ namespace ts {
if (!couldContainTypeVariables(target)) {
return;
}
if (source === wildcardType) {
source = getWildcardInstantiation(target);
if (source === neverType || source === wildcardType) {
// We are inferring from 'never' or the wildcard type. We want to infer this
// type for every type parameter referenced in the target type, so we infer from
// target to itself with a flag we check when recording candidates.
const savePriority = priority;
priority |= source === neverType ? InferencePriority.Never : InferencePriority.Wildcard;
inferFromTypes(target, target);
priority = savePriority;
return;
}
if (source.aliasSymbol && source.aliasTypeArguments && source.aliasSymbol === target.aliasSymbol) {
// Source and target are types originating in the same generic type alias declaration.
@@ -11560,17 +11567,21 @@ namespace ts {
const inference = getInferenceInfoForType(target);
if (inference) {
if (!inference.isFixed) {
if (inference.priority === undefined || priority < inference.priority) {
const p = priority & InferencePriority.Mask;
if (inference.priority === undefined || p < inference.priority) {
inference.candidates = undefined;
inference.contraCandidates = undefined;
inference.priority = priority;
inference.priority = p;
}
if (priority === inference.priority) {
if (p === inference.priority) {
const candidate = priority & InferencePriority.Never ? neverType :
priority & InferencePriority.Wildcard ? wildcardType :
source;
if (contravariant) {
inference.contraCandidates = append(inference.contraCandidates, source);
inference.contraCandidates = append(inference.contraCandidates, candidate);
}
else {
inference.candidates = append(inference.candidates, source);
inference.candidates = append(inference.candidates, candidate);
}
}
if (!(priority & InferencePriority.ReturnType) && target.flags & TypeFlags.TypeParameter && !isTypeParameterAtTopLevel(originalTarget, <TypeParameter>target)) {

3
src/compiler/types.ts
View File

@@ -3915,6 +3915,9 @@ namespace ts {
ReturnType = 1 << 2, // Inference made from return type of generic function
NoConstraints = 1 << 3, // Don't infer from constraints of instantiable types
AlwaysStrict = 1 << 4, // Always use strict rules for contravariant inferences
Wildcard = 1 << 5, // Inferring from wildcard type
Never = 1 << 6, // Inferring from never type
Mask = NakedTypeVariable | MappedType | ReturnType,
}
/* @internal */