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Merge pull request #24310 from Microsoft/nonWideningLiteralInferences

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Non-widening literal type inferences
This commit is contained in:
Anders Hejlsberg
2018-05-22 06:56:34 -07:00
committed by GitHub
parent a9e89ce3f1 b31c414a31
commit f52c4af448
20 changed files with 443 additions and 74 deletions
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src/compiler/checker.ts
+9 -5
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@@ -9286,8 +9286,10 @@ namespace ts {
return type;
}
function getRegularTypeOfLiteralType(type: Type) {
return type.flags & TypeFlags.StringOrNumberLiteral && type.flags & TypeFlags.FreshLiteral ? (<LiteralType>type).regularType : type;
function getRegularTypeOfLiteralType(type: Type): Type {
return type.flags & TypeFlags.StringOrNumberLiteral && type.flags & TypeFlags.FreshLiteral ? (<LiteralType>type).regularType :
type.flags & TypeFlags.Union ? getUnionType(sameMap((<UnionType>type).types, getRegularTypeOfLiteralType)) :
type;
}
function getLiteralType(value: string | number, enumId?: number, symbol?: Symbol) {
@@ -12774,10 +12776,12 @@ namespace ts {
// all inferences were made to top-level occurrences of the type parameter, and
// the type parameter has no constraint or its constraint includes no primitive or literal types, and
// the type parameter was fixed during inference or does not occur at top-level in the return type.
const widenLiteralTypes = inference.topLevel &&
!hasPrimitiveConstraint(inference.typeParameter) &&
const primitiveConstraint = hasPrimitiveConstraint(inference.typeParameter);
const widenLiteralTypes = !primitiveConstraint && inference.topLevel &&
(inference.isFixed || !isTypeParameterAtTopLevel(getReturnTypeOfSignature(signature), inference.typeParameter));
const baseCandidates = widenLiteralTypes ? sameMap(candidates, getWidenedLiteralType) : candidates;
const baseCandidates = primitiveConstraint ? sameMap(candidates, getRegularTypeOfLiteralType) :
widenLiteralTypes ? sameMap(candidates, getWidenedLiteralType) :
candidates;
// If all inferences were made from contravariant positions, infer a common subtype. Otherwise, if
// union types were requested or if all inferences were made from the return type position, infer a
// union type. Otherwise, infer a common supertype.