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Allow nested conditionals to be related via constraints (#37208)

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* Allow nested conditionals to be related via constraints

* Delete word in comment
This commit is contained in:
Wesley Wigham
2020-03-19 12:03:50 -07:00
committed by GitHub
parent a83ce339c9
commit c513a4adea
9 changed files with 486 additions and 210 deletions
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16
src/compiler/checker.ts
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@@ -16040,6 +16040,8 @@ namespace ts {
}
}
else {
// conditionals aren't related to one another via distributive constraint as it is much too inaccurate and allows way
// more assignments than are desirable (since it maps the source check type to its constraint, it loses information)
const distributiveConstraint = getConstraintOfDistributiveConditionalType(<ConditionalType>source);
if (distributiveConstraint) {
if (result = isRelatedTo(distributiveConstraint, target, reportErrors)) {
@@ -16047,12 +16049,14 @@ namespace ts {
return result;
}
}
const defaultConstraint = getDefaultConstraintOfConditionalType(<ConditionalType>source);
if (defaultConstraint) {
if (result = isRelatedTo(defaultConstraint, target, reportErrors)) {
resetErrorInfo(saveErrorInfo);
return result;
}
}
// conditionals _can_ be related to one another via normal constraint, as, eg, `A extends B ? O : never` should be assignable to `O`
// when `O` is a conditional (`never` is trivially aissgnable to `O`, as is `O`!).
const defaultConstraint = getDefaultConstraintOfConditionalType(<ConditionalType>source);
if (defaultConstraint) {
if (result = isRelatedTo(defaultConstraint, target, reportErrors)) {
resetErrorInfo(saveErrorInfo);
return result;
}
}
}