fix self-check

Author: Andarist

src/compiler/checker.ts

@@ -18112,12 +18112,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     // reduced we'll never reduce again, so this occurs at most once.
                     result = getIntersectionType(typeSet, flags, aliasSymbol, aliasTypeArguments);
                 }
-                else if (every(typeSet, t => !!(t.flags & TypeFlags.Union && (t as UnionType).types[0].flags & TypeFlags.Undefined))) {
+                else if (every(typeSet, (t): boolean => !!(t.flags & TypeFlags.Union && (t as UnionType).types[0].flags & TypeFlags.Undefined))) {
                     const containedUndefinedType = some(typeSet, containsMissingType) ? missingType : undefinedType;
                     removeFromEach(typeSet, TypeFlags.Undefined);
                     result = getUnionType([getIntersectionType(typeSet, flags), containedUndefinedType], UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
                 }
-                else if (every(typeSet, t => !!(t.flags & TypeFlags.Union && ((t as UnionType).types[0].flags & TypeFlags.Null || (t as UnionType).types[1].flags & TypeFlags.Null)))) {
+                else if (every(typeSet, (t): boolean => !!(t.flags & TypeFlags.Union && ((t as UnionType).types[0].flags & TypeFlags.Null || (t as UnionType).types[1].flags & TypeFlags.Null)))) {
                     removeFromEach(typeSet, TypeFlags.Null);
                     result = getUnionType([getIntersectionType(typeSet, flags), nullType], UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
                 }
@@ -18434,7 +18434,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
         newTexts.push(text);
         if (every(newTexts, t => t === "")) {
-            if (every(newTypes, t => !!(t.flags & TypeFlags.String))) {
+            if (every(newTypes, (t): boolean => !!(t.flags & TypeFlags.String))) {
                 return stringType;
             }
             // Normalize `${Mapping<xxx>}` into Mapping<xxx>