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Document assignment to aliasSymbol in getUnionTypeFromSortedList #17434

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Merged
merged 2 commits into from
Sep 7, 2017
Merged

Document assignment to aliasSymbol in getUnionTypeFromSortedList #17434

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abfeac9
Document assignment to aliasSymbol in getUnionTypeFromSortedList
Jul 26, 2017
bb29f97
Update wording
Aug 29, 2017
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8 changes: 7 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7359,6 +7359,12 @@ namespace ts {
type = <UnionType>createType(TypeFlags.Union | propagatedFlags);
unionTypes.set(id, type);
type.types = types;
/*
Note: This is the alias symbol (or lack thereof) that we see when we first encounter this union type.
For aliases of identical unions, eg `type T = A | B; type U = A | B`, the symbol of the first alias encountered is the aliasSymbol.
(In the language service, the order may depend on the order in which a user takes actions, such as hovering over symbols.)
It's important that we create equivalent union types only once, so that's an unfortunate side effect.
*/
type.aliasSymbol = aliasSymbol;
type.aliasTypeArguments = aliasTypeArguments;
}
Expand Down Expand Up @@ -7452,7 +7458,7 @@ namespace ts {
type = <IntersectionType>createType(TypeFlags.Intersection | propagatedFlags);
intersectionTypes.set(id, type);
type.types = typeSet;
type.aliasSymbol = aliasSymbol;
type.aliasSymbol = aliasSymbol; // See comment in `getUnionTypeFromSortedList`.
type.aliasTypeArguments = aliasTypeArguments;
}
return type;
Expand Down