sync with resolver

Author: dcodeIO

src/program.ts

@@ -633,6 +633,14 @@ export class Program extends DiagnosticEmitter {
   }
   private _stringInstance: Class | null = null;
 
+  /** Gets the standard `RefString` instance. */
+  get refStringInstance(): Class {
+    let cached = this._refStringInstance;
+    if (!cached) this._refStringInstance = cached = this.requireClass(CommonNames.RefString);
+    return cached;
+  }
+  private _refStringInstance: Class | null = null;
+
   /** Gets the standard `RegExp` instance. */
   get regexpInstance(): Class {
     let cached = this._regexpInstance;

src/resolver.ts

@@ -2343,6 +2343,8 @@ export class Resolver extends DiagnosticEmitter {
       }
       case LiteralKind.String:
       case LiteralKind.Template: {
+        // Resolve to stringref if context indicates
+        if (ctxType.kind == TypeKind.String) return this.program.refStringInstance;
         return this.program.stringInstance;
       }
       case LiteralKind.RegExp: {