maxmustermann/TypeScript
1
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

Make inferences to union types containing multiple naked type variables

Browse source
This commit is contained in:
Anders Hejlsberg 2019-02-10 15:07:01 -08:00
parent bbf559b9c7
commit 1f32139811
1 changed files with 8 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

27
src/compiler/checker.ts
View file

@ -14472,26 +14472,15 @@ namespace ts {
inferFromTypes(source, getUnionType([getTrueTypeFromConditionalType(<ConditionalType>target), getFalseTypeFromConditionalType(<ConditionalType>target)]));
}
else if (target.flags & TypeFlags.UnionOrIntersection) {
const targetTypes = (<UnionOrIntersectionType>target).types;
let typeVariableCount = 0;
let typeVariable: TypeParameter | IndexedAccessType | undefined;
// First infer to each type in union or intersection that isn't a type variable
for (const t of targetTypes) {
if (getInferenceInfoForType(t)) {
typeVariable = <InstantiableType>t;
typeVariableCount++;
}
else {
inferFromTypes(source, t);
}
}
// Next, if target containings a single naked type variable, make a secondary inference to that type
// variable. This gives meaningful results for union types in co-variant positions and intersection
// types in contra-variant positions (such as callback parameters).
if (typeVariableCount === 1) {
for (const t of (<UnionOrIntersectionType>target).types) {
const savePriority = priority;
priority |= InferencePriority.NakedTypeVariable;
inferFromTypes(source, typeVariable!);
// Inferences directly to naked type variables are given lower priority as they are
// less specific. For example, when inferring from Promise<string> to T | Promise<T>,
// we want to infer string for T, not Promise<string> | string.
if (getInferenceInfoForType(t)) {
priority |= InferencePriority.NakedTypeVariable;
}
inferFromTypes(source, t);
priority = savePriority;
}
}