Handle multiple levesl of substitutions and indexed accesses in getActualTypeVariable

Author: jakebailey

src/compiler/checker.ts

@@ -17624,7 +17624,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function getActualTypeVariable(type: Type): Type {
         if (type.flags & TypeFlags.Substitution) {
-            return (type as SubstitutionType).baseType;
+            return getActualTypeVariable((type as SubstitutionType).baseType);
         }
         if (type.flags & TypeFlags.IndexedAccess && (
             (type as IndexedAccessType).objectType.flags & TypeFlags.Substitution ||

tests/baselines/reference/inferRestArgumentsMappedTuple.errors.txt

@@ -26,7 +26,7 @@ declare function extractPrimitivesOld<Tuple extends any[]>(...mappedTypes: Tuple
 // [string, number]
 const myPrimitiveTupleOld: [string, number] = extractPrimitivesOld({ primitive: "" }, { primitive: 0 });
 >myPrimitiveTupleOld : [string, number]
->extractPrimitivesOld({ primitive: "" }, { primitive: 0 }) : [unknown, unknown]
+>extractPrimitivesOld({ primitive: "" }, { primitive: 0 }) : [string, number]
 >extractPrimitivesOld : <Tuple extends any[]>(...mappedTypes: TupleMapperOld<Tuple>) => Tuple
 >{ primitive: "" } : { primitive: string; }
 >primitive : string