allow generic arrays to be indexed with concrete string numerics

Author: Andarist

src/compiler/checker.ts

@@ -17744,7 +17744,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const propertyTypes = map(getPropertiesOfType(type), prop => getLiteralTypeFromProperty(prop, include));
         const indexKeyTypes = map(getIndexInfosOfType(type), info =>
             info !== enumNumberIndexInfo && isKeyTypeIncluded(info.keyType, include) ?
-                info.keyType === stringType && include & TypeFlags.Number ? stringOrNumberType : info.keyType : neverType);
+                info.keyType === stringType && include & TypeFlags.Number ? stringOrNumberType : info.keyType === numberType ? getUnionType([numberType, numericStringType]) : info.keyType : neverType);
         return getUnionType(concatenate(propertyTypes, indexKeyTypes), UnionReduction.Literal, /*aliasSymbol*/ undefined, /*aliasTypeArguments*/ undefined, origin);
     }
 

tests/baselines/reference/typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.symbols

@@ -0,0 +1,8 @@
+//// [tests/cases/compiler/typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts] ////
+
+=== typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts ===
+type Test1<A extends any[]> = A["0"];
+>Test1 : Symbol(Test1, Decl(typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts, 0, 0))
+>A : Symbol(A, Decl(typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts, 0, 11))
+>A : Symbol(A, Decl(typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts, 0, 11))
+

tests/baselines/reference/typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.types

@@ -0,0 +1,6 @@
+//// [tests/cases/compiler/typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts] ////
+
+=== typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts ===
+type Test1<A extends any[]> = A["0"];
+>Test1 : Test1<A>
+

tests/cases/compiler/typeParameterConstrainedToArrayIndexableByConcreteStringNumeric.ts

@@ -0,0 +1,4 @@
+// @strict: true
+// @noEmit: true
+
+type Test1<A extends any[]> = A["0"];