Make T[K] yield never when T is never

ahejlsberg · ahejlsberg · commit 8ff8008fc0f9 · 2018-08-09T16:31:54.000-04:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -9140,7 +9140,7 @@ namespace ts {
                 }
             }
             if (!(indexType.flags & TypeFlags.Nullable) && isTypeAssignableToKind(indexType, TypeFlags.StringLike | TypeFlags.NumberLike | TypeFlags.ESSymbolLike)) {
-                if (isTypeAny(objectType)) {
+                if (objectType.flags & (TypeFlags.Any | TypeFlags.Never)) {
                     return objectType;
                 }
                 const indexInfo = isTypeAssignableToKind(indexType, TypeFlags.NumberLike) && getIndexInfoOfType(objectType, IndexKind.Number) ||
diff --git a/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.errors.txt b/tests/baselines/reference/nonPrimitiveConstraintOfIndexAccessType.errors.txt
@@ -3,6 +3,7 @@ tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessTy
 tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts(9,5): error TS2322: Type 'string' is not assignable to type 'T[P]'.
 tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts(12,5): error TS2322: Type 'string' is not assignable to type 'T[P]'.
 tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts(15,5): error TS2322: Type 'string' is not assignable to type 'T[P]'.
+  Type 'string' is not assignable to type 'never'.
 tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts(18,5): error TS2322: Type 'string' is not assignable to type 'T[P]'.
 tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts(21,5): error TS2322: Type 'string' is not assignable to type 'T[P]'.
 tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessType.ts(24,5): error TS2322: Type 'string' is not assignable to type 'T[P]'.
@@ -37,6 +38,7 @@ tests/cases/conformance/types/nonPrimitive/nonPrimitiveConstraintOfIndexAccessTy
         tp = s;
         ~~
 !!! error TS2322: Type 'string' is not assignable to type 'T[P]'.
+!!! error TS2322:   Type 'string' is not assignable to type 'never'.
     }
     function k<T extends number, P extends keyof T>(s: string, tp: T[P]): void {
         tp = s;

Original file line number	Diff line number	Diff line change
`@@ -9140,7 +9140,7 @@ namespace ts {`
`9140`	`9140`	`}`
`9141`	`9141`	`}`
`9142`	`9142`	`if (!(indexType.flags & TypeFlags.Nullable) && isTypeAssignableToKind(indexType, TypeFlags.StringLike \| TypeFlags.NumberLike \| TypeFlags.ESSymbolLike)) {`
`9143`		`- if (isTypeAny(objectType)) {`
	`9143`	`+ if (objectType.flags & (TypeFlags.Any \| TypeFlags.Never)) {`
`9144`	`9144`	`return objectType;`
`9145`	`9145`	`}`
`9146`	`9146`	`const indexInfo = isTypeAssignableToKind(indexType, TypeFlags.NumberLike) && getIndexInfoOfType(objectType, IndexKind.Number) \|\|`