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Document assignment to aliasSymbol in getUnionTypeFromSortedList (#17434)

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* Document assignment to aliasSymbol in getUnionTypeFromSortedList

* Update wording
This commit is contained in:
Andy 2017-09-07 12:39:13 -07:00 committed by Mohamed Hegazy
parent 448d75c08f
commit 508cde0ea1
1 changed files with 7 additions and 1 deletions
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8
src/compiler/checker.ts
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@ -7435,6 +7435,12 @@ 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;
}
@ -7528,7 +7534,7 @@ 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;