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Document assignment to aliasSymbol in getUnionTypeFromSortedList #17434

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Merged
mhegazy merged 2 commits into from
Sep 7, 2017
Merged

Document assignment to aliasSymbol in getUnionTypeFromSortedList #17434

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Document assignment to aliasSymbol in getUnionTypeFromSortedList
Jul 26, 2017
bb29f97
Update wording
Aug 29, 2017
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7 changes: 6 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 +7359,11 @@ 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.
If there exist both `type T = number | boolean` and `type U = number | boolean`, it is arbitrary which one gets the aliasSymbol.
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@sandersn sandersn Aug 29, 2017

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I would write this line as

For aliases of identical unions, eg type T = A | B; type U = A | B, the symbol of the first alias encountered is the aliasSymbol.

This is technically true even for the language server, but "first alias encountered" depends on the order of actions by the user.

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 +7457,7 @@ 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;
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