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Fixed an issue with unsound indexed access on unknown type param#49729

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Mateusz Burzyński (Andarist) wants to merge 1 commit into from
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Fixed an issue with unsound indexed access on unknown type param #49729

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2 changes: 1 addition & 1 deletion src/compiler/checker.ts
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Expand Up@@ -28892,7 +28892,7 @@ namespace ts {
return errorType;
}
const facts = getTypeFacts(type);
if (facts & TypeFacts.IsUndefinedOrNull) {
if (facts & TypeFacts.IsUndefinedOrNull || type.flags & (TypeFlags.Intersection | TypeFlags.Instantiable) && (getBaseConstraintOfType(type) || unknownType) === unknownType) {

@AndaristMateusz Burzyński (Andarist)Jun 29, 2022

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I'm not super sure if this is the best check, I've based this on the logic from getTypeFacts:
https://github.dev/microsoft/TypeScript/blob/b379e7fc791fc8646d9d255adce5127a6ab83099/src/compiler/checker.ts#L23562-L23564

In fact, I think this case probably should report a similar error like the one introduced here:
https://github.com/microsoft/TypeScript/pull/49119/files#diff-d9ab6589e714c71e657f601cf30ff51dfc607fc98419bf72e04f6b0fa92cc4b8R18815-R18817
Note that this logic has been further adjusted in:
https://github.com/microsoft/TypeScript/pull/49481/files#diff-d9ab6589e714c71e657f601cf30ff51dfc607fc98419bf72e04f6b0fa92cc4b8R18795

cc Anders Hejlsberg (@ahejlsberg)

reportError(node, facts);
const t = getNonNullableType(type);
return t.flags & (TypeFlags.Nullable | TypeFlags.Never) ? errorType : t;
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26 changes: 26 additions & 0 deletions tests/baselines/reference/genericUnknownTypeParamWithKeyofIndexedAccess.errors.txt
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@@ -0,0 +1,26 @@
tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts(2,12): error TS2531: Object is possibly 'null'.
tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts(5,12): error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts(8,12): error TS2531: Object is possibly 'null'.
tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts(11,13): error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.


==== tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts (4 errors) ====
function test<T, K extends keyof T>(t: T, k: K) {
return t[k];
~
!!! error TS2531: Object is possibly 'null'.
}

test(null, 'foo')

@AndaristMateusz Burzyński (Andarist)Jun 29, 2022

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I've included those calls as there was a temporary regression related to this, you can check out here. I've figured out that this might be worth it to add here as part of the regression tests

~~~~~
!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.

function test2<T extends unknown, K extends keyof T>(t: T, k: K) {
return t[k];
~
!!! error TS2531: Object is possibly 'null'.
}

test2(null, 'foo')
~~~~~
!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
37 changes: 37 additions & 0 deletions tests/baselines/reference/genericUnknownTypeParamWithKeyofIndexedAccess.symbols
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@@ -0,0 +1,37 @@
=== tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts ===
function test<T, K extends keyof T>(t: T, k: K) {
>test : Symbol(test, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 0))
>T : Symbol(T, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 14))
>K : Symbol(K, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 16))
>T : Symbol(T, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 14))
>t : Symbol(t, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 36))
>T : Symbol(T, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 14))
>k : Symbol(k, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 41))
>K : Symbol(K, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 16))

return t[k];
>t : Symbol(t, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 36))
>k : Symbol(k, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 41))
}

test(null, 'foo')
>test : Symbol(test, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 0, 0))

function test2<T extends unknown, K extends keyof T>(t: T, k: K) {
>test2 : Symbol(test2, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 4, 17))
>T : Symbol(T, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 15))
>K : Symbol(K, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 33))
>T : Symbol(T, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 15))
>t : Symbol(t, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 53))
>T : Symbol(T, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 15))
>k : Symbol(k, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 58))
>K : Symbol(K, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 33))

return t[k];
>t : Symbol(t, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 53))
>k : Symbol(k, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 6, 58))
}

test2(null, 'foo')
>test2 : Symbol(test2, Decl(genericUnknownTypeParamWithKeyofIndexedAccess.ts, 4, 17))

35 changes: 35 additions & 0 deletions tests/baselines/reference/genericUnknownTypeParamWithKeyofIndexedAccess.types
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@@ -0,0 +1,35 @@
=== tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts ===
function test<T, K extends keyof T>(t: T, k: K) {
>test : <T, K extends keyof T>(t: T, k: K) => NonNullable<T>[K]
>t : T
>k : K

return t[k];
>t[k] : NonNullable<T>[K]
>t : T
>k : K
}

test(null, 'foo')
>test(null, 'foo') : never
>test : <T, K extends keyof T>(t: T, k: K) => NonNullable<T>[K]
>null : null
>'foo' : "foo"

function test2<T extends unknown, K extends keyof T>(t: T, k: K) {
>test2 : <T extends unknown, K extends keyof T>(t: T, k: K) => NonNullable<T>[K]
>t : T
>k : K

return t[k];
>t[k] : NonNullable<T>[K]
>t : T
>k : K
}

test2(null, 'foo')
>test2(null, 'foo') : never
>test2 : <T extends unknown, K extends keyof T>(t: T, k: K) => NonNullable<T>[K]
>null : null
>'foo' : "foo"

14 changes: 14 additions & 0 deletions tests/cases/compiler/genericUnknownTypeParamWithKeyofIndexedAccess.ts
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@@ -0,0 +1,14 @@
// @strict: true
// @noEmit: true

function test<T, K extends keyof T>(t: T, k: K) {
return t[k];
}

test(null, 'foo')

function test2<T extends unknown, K extends keyof T>(t: T, k: K) {
return t[k];
}

test2(null, 'foo')