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Erase 'infer T' locations in conditional type constraints

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This commit is contained in:
Anders Hejlsberg 2018-03-28 13:16:11 -07:00
parent 66bf5b4e9d
commit dc3eb3c27e
2 changed files with 16 additions and 2 deletions
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14
src/compiler/checker.ts
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@ -6233,7 +6233,7 @@ namespace ts {
}
function getDefaultConstraintOfConditionalType(type: ConditionalType) {
return getUnionType([getTrueTypeFromConditionalType(type), getFalseTypeFromConditionalType(type)]);
return getUnionType([getInferredTrueTypeFromConditionalType(type), getFalseTypeFromConditionalType(type)]);
}
function getConstraintOfDistributiveConditionalType(type: ConditionalType): Type {
@ -8343,16 +8343,19 @@ namespace ts {
// If this is a distributive conditional type and the check type is generic we need to defer
// resolution of the conditional type such that a later instantiation will properly distribute
// over union types.
if (!root.isDistributive || !maybeTypeOfKind(checkType, TypeFlags.Instantiable)) {
const isDeferred = root.isDistributive && maybeTypeOfKind(checkType, TypeFlags.Instantiable);
let combinedMapper: TypeMapper;
if (root.inferTypeParameters) {
const context = createInferenceContext(root.inferTypeParameters, /*signature*/ undefined, InferenceFlags.None);
if (!isDeferred) {
// We don't want inferences from constraints as they may cause us to eagerly resolve the
// conditional type instead of deferring resolution. Also, we always want strict function
// types rules (i.e. proper contravariance) for inferences.
inferTypes(context.inferences, checkType, extendsType, InferencePriority.NoConstraints | InferencePriority.AlwaysStrict);
}
combinedMapper = combineTypeMappers(mapper, context);
}
if (!isDeferred) {
// Return union of trueType and falseType for 'any' since it matches anything
if (checkType.flags & TypeFlags.Any) {
return getUnionType([instantiateType(root.trueType, combinedMapper || mapper), instantiateType(root.falseType, mapper)]);
@ -8381,6 +8384,7 @@ namespace ts {
result.checkType = erasedCheckType;
result.extendsType = extendsType;
result.mapper = mapper;
result.combinedMapper = combinedMapper;
result.aliasSymbol = root.aliasSymbol;
result.aliasTypeArguments = instantiateTypes(root.aliasTypeArguments, mapper);
return result;
@ -8394,6 +8398,12 @@ namespace ts {
return type.resolvedFalseType || (type.resolvedFalseType = instantiateType(type.root.falseType, type.mapper));
}
function getInferredTrueTypeFromConditionalType(type: ConditionalType) {
return type.combinedMapper ?
type.resolvedInferredTrueType || (type.resolvedInferredTrueType = instantiateType(type.root.trueType, type.combinedMapper)) :
getTrueTypeFromConditionalType(type);
}
function getInferTypeParameters(node: ConditionalTypeNode): TypeParameter[] {
let result: TypeParameter[];
if (node.locals) {

4
src/compiler/types.ts
View File

@ -3878,7 +3878,11 @@ namespace ts {
resolvedTrueType?: Type;
resolvedFalseType?: Type;
/* @internal */
resolvedInferredTrueType?: Type;
/* @internal */
mapper?: TypeMapper;
/* @internal */
combinedMapper?: TypeMapper;
}
// Type parameter substitution (TypeFlags.Substitution)