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Improve algorithm for inferring to union types

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This commit is contained in:
Anders Hejlsberg 2019-07-16 16:29:52 -07:00
parent d4765523f0
commit d8b191a671
1 changed files with 48 additions and 3 deletions
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51
src/compiler/checker.ts
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@ -15458,6 +15458,7 @@ namespace ts {
let visited: Map<boolean>;
let bivariant = false;
let propagationType: Type;
let inferenceCount = 0;
let allowComplexConstraintInference = true;
inferFromTypes(originalSource, originalTarget);
@ -15561,6 +15562,7 @@ namespace ts {
clearCachedInferences(inferences);
}
}
inferenceCount++;
return;
}
else {
@ -15610,13 +15612,16 @@ namespace ts {
inferFromTypes(getTrueTypeFromConditionalType(<ConditionalType>source), getTrueTypeFromConditionalType(<ConditionalType>target));
inferFromTypes(getFalseTypeFromConditionalType(<ConditionalType>source), getFalseTypeFromConditionalType(<ConditionalType>target));
}
else if (target.flags & TypeFlags.Union) {
inferToUnionType(source, <UnionType>target);
}
else if (target.flags & TypeFlags.Intersection) {
inferToMultipleTypes(source, (<UnionOrIntersectionType>target).types, /*isIntersection*/ true);
}
else if (target.flags & TypeFlags.Conditional && !contravariant) {
const targetTypes = [getTrueTypeFromConditionalType(<ConditionalType>target), getFalseTypeFromConditionalType(<ConditionalType>target)];
inferToMultipleTypes(source, targetTypes, /*isIntersection*/ false);
}
else if (target.flags & TypeFlags.UnionOrIntersection) {
inferToMultipleTypes(source, (<UnionOrIntersectionType>target).types, !!(target.flags & TypeFlags.Intersection));
}
else if (source.flags & TypeFlags.Union) {
// Source is a union or intersection type, infer from each constituent type
const sourceTypes = (<UnionOrIntersectionType>source).types;
@ -15742,6 +15747,46 @@ namespace ts {
}
}
function inferToUnionType(source: Type, target: UnionType) {
const sources = source.flags & TypeFlags.Union ? (<UnionType>source).types : [source];
const matched = new Array<boolean>(sources.length);
let typeVariableCount = 0;
// First infer to types that are not naked type variables. For each source type we
// track whether inferences were made from that particular type to some target.
for (const t of target.types) {
if (getInferenceInfoForType(t)) {
typeVariableCount++;
}
else {
for (let i = 0; i < sources.length; i++) {
const count = inferenceCount;
inferFromTypes(sources[i], t);
if (count !== inferenceCount) matched[i] = true;
}
}
}
// If there are naked type variables in the target, create a union of the source types
// from which no inferences have been made so far and infer from that union to each naked
// type variable. If there is more than one naked type variable, give lower priority to
// the inferences as they are less specific.
if (typeVariableCount > 0) {
const unmatched = flatMap(sources, (s, i) => matched![i] ? undefined : s);
if (unmatched.length) {
const s = getUnionType(unmatched);
const savePriority = priority;
if (typeVariableCount > 1) {
priority |= InferencePriority.NakedTypeVariable;
}
for (const t of target.types) {
if (getInferenceInfoForType(t)) {
inferFromTypes(s, t);
}
}
priority = savePriority;
}
}
}
function inferToMappedType(source: Type, target: MappedType, constraintType: Type): boolean {
if (constraintType.flags & TypeFlags.Union) {
let result = false;