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Discard constraint inferences of the type parameter itself

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This commit is contained in:
Anders Hejlsberg
2018-02-07 06:57:23 -08:00
parent 39db00e588
commit a44ab96468
1 changed files with 16 additions and 7 deletions
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23
src/compiler/checker.ts
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@@ -6964,7 +6964,7 @@ namespace ts {
}
function getInferredTypeParameterConstraint(typeParameter: TypeParameter) {
let constraints: Type[];
let inferences: Type[];
if (typeParameter.symbol) {
for (const declaration of typeParameter.symbol.declarations) {
// When an 'infer T' declaration is immediately contained in a type reference node
@@ -6977,17 +6977,26 @@ namespace ts {
if (typeParameters) {
const index = typeReference.typeArguments.indexOf(<TypeNode>declaration.parent);
if (index < typeParameters.length) {
const constraint = getConstraintOfTypeParameter(typeParameters[index]);
if (constraint) {
const declaredConstraint = getConstraintOfTypeParameter(typeParameters[index]);
if (declaredConstraint) {
// Type parameter constraints can reference other type parameters so
// constraints need to be instantiated. If instantiation produces the
// type parameter itself, we discard that inference. For example, in
// type Foo<T extends string, U extends T> = [T, U];
// type Bar<T> = T extends Foo<infer X, infer X> ? Foo<X, X> : T;
// the instantiated constraint for U is X, so we discard that inference.
const mapper = createTypeMapper(typeParameters, getEffectiveTypeArguments(typeReference, typeParameters));
constraints = append(constraints, instantiateType(constraint, mapper));
const constraint = instantiateType(declaredConstraint, mapper);
if (constraint !== typeParameter) {
inferences = append(inferences, constraint);
}
}
}
}
}
}
}
return constraints && getIntersectionType(constraints);
return inferences && getIntersectionType(inferences);
}
function getConstraintFromTypeParameter(typeParameter: TypeParameter): Type {
@@ -20197,8 +20206,8 @@ namespace ts {
}
function getEffectiveTypeArguments(node: TypeReferenceNode | ExpressionWithTypeArguments, typeParameters: TypeParameter[]) {
const minTypeArgumentCount = getMinTypeArgumentCount(typeParameters);
return fillMissingTypeArguments(map(node.typeArguments, getTypeFromTypeNode), typeParameters, minTypeArgumentCount, isInJavaScriptFile(node));
return fillMissingTypeArguments(map(node.typeArguments, getTypeFromTypeNode), typeParameters,
getMinTypeArgumentCount(typeParameters), isInJavaScriptFile(node));
}
function checkTypeArgumentConstraints(node: TypeReferenceNode | ExpressionWithTypeArguments, typeParameters: TypeParameter[]): boolean {