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Fixup restrictive instantiations to actually erase type parameter constraints #29592

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Merged
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Jan 25, 2019
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Fixup restrictive instantiations to actually erase type parameter constraints #29592

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6 changes: 5 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -10636,7 +10636,11 @@ namespace ts {
}

function getRestrictiveTypeParameter(tp: TypeParameter) {
return !tp.constraint ? tp : tp.restrictiveInstantiation || (tp.restrictiveInstantiation = createTypeParameter(tp.symbol));
return tp.constraint === unknownType ? tp : tp.restrictiveInstantiation || (
tp.restrictiveInstantiation = createTypeParameter(tp.symbol),
(tp.restrictiveInstantiation as TypeParameter).constraint = unknownType,
tp.restrictiveInstantiation
);
}

function restrictiveMapper(type: Type) {
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5 changes: 1 addition & 4 deletions tests/baselines/reference/typeParameterIndirectlyConstrainedToItself.errors.txt
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Expand Up @@ -25,10 +25,9 @@ tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterInd
tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterIndirectlyConstrainedToItself.ts(16,47): error TS2313: Type parameter 'V' has a circular constraint.
tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterIndirectlyConstrainedToItself.ts(18,32): error TS2313: Type parameter 'T' has a circular constraint.
tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterIndirectlyConstrainedToItself.ts(18,45): error TS2313: Type parameter 'V' has a circular constraint.
tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterIndirectlyConstrainedToItself.ts(23,24): error TS2313: Type parameter 'S' has a circular constraint.


==== tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterIndirectlyConstrainedToItself.ts (28 errors) ====
==== tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterIndirectlyConstrainedToItself.ts (27 errors) ====
class C<U extends T, T extends U> { }
~
!!! error TS2313: Type parameter 'U' has a circular constraint.
Expand Down Expand Up @@ -106,6 +105,4 @@ tests/cases/conformance/types/typeParameters/typeParameterLists/typeParameterInd

type Foo<T> = [T] extends [number] ? {} : {};
function foo<S extends Foo<S>>() {}
~~~~~~
!!! error TS2313: Type parameter 'S' has a circular constraint.

2 changes: 1 addition & 1 deletion tests/baselines/reference/typeParameterIndirectlyConstrainedToItself.types
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Expand Up @@ -38,5 +38,5 @@ type Foo<T> = [T] extends [number] ? {} : {};
>Foo : Foo<T>

function foo<S extends Foo<S>>() {}
>foo : <S>() => void
>foo : <S extends Foo<S>>() => void