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Reinstate type simplification for 'keyof T[K]' as target in relation

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This commit is contained in:
Anders Hejlsberg 2018-04-24 10:02:34 -07:00
parent b1baca565b
commit e71afc32ad
1 changed files with 8 additions and 5 deletions
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13
src/compiler/checker.ts
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@ -10482,11 +10482,14 @@ namespace ts {
}
}
// A type S is assignable to keyof T if S is assignable to keyof C, where C is the
// constraint of T.
const constraint = getConstraintForRelation((<IndexType>target).type);
if (constraint) {
if (result = isRelatedTo(source, getIndexType(constraint, (target as IndexType).stringsOnly), reportErrors)) {
return result;
// simplified form of T or, if T doesn't simplify, the constraint of T.
if (relation !== definitelyAssignableRelation) {
const simplified = getSimplifiedType((<IndexType>target).type);
const constraint = simplified !== (<IndexType>target).type ? simplified : getConstraintOfType((<IndexType>target).type);
if (constraint) {
if (result = isRelatedTo(source, getIndexType(constraint, (target as IndexType).stringsOnly), reportErrors)) {
return result;
}
}
}
}