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Merge pull request #30857 from Microsoft/fixInferenceToIntersection (#30968)

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Fix inference to intersections
This commit is contained in:
Ryan Cavanaugh
2019-04-16 13:25:10 -07:00
committed by GitHub
parent e0f136bf7b
commit f0de46bdd3
7 changed files with 115 additions and 28 deletions
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src/compiler/checker.ts
+21 -6
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@@ -14709,15 +14709,30 @@ namespace ts {
inferFromTypes(source, (<ConditionalType>target).falseType);
}
else if (target.flags & TypeFlags.UnionOrIntersection) {
// We infer from types that are not naked type variables first so that inferences we
// make from nested naked type variables and given slightly higher priority by virtue
// of being first in the candidates array.
let typeVariableCount = 0;
for (const t of (<UnionOrIntersectionType>target).types) {
const savePriority = priority;
// 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;
typeVariableCount++;
}
else {
inferFromTypes(source, t);
}
}
// 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. For intersection types
// we only infer to single naked type variables.
if (target.flags & TypeFlags.Union ? typeVariableCount !== 0 : typeVariableCount === 1) {
const savePriority = priority;
priority |= InferencePriority.NakedTypeVariable;
for (const t of (<UnionOrIntersectionType>target).types) {
if (getInferenceInfoForType(t)) {
inferFromTypes(source, t);
}
}
inferFromTypes(source, t);
priority = savePriority;
}
}