1.1 --- a/rt/vm/src/main/java/org/apidesign/vm4brwsr/VM.java	Sun Nov 09 10:36:08 2014 +0100
     1.2 +++ b/rt/vm/src/main/java/org/apidesign/vm4brwsr/VM.java	Thu Nov 27 20:23:35 2014 +0100
     1.3 @@ -35,6 +35,7 @@
     1.4      private final ExportedSymbols exportedSymbols;
     1.5      private final StringArray invokerMethods;
     1.6      private final StringArray asBinary;
     1.7 +    int exportedCount;
     1.8  
     1.9      private VM(
    1.10          Appendable out, Bck2Brwsr.Resources resources, 
    1.11 @@ -160,6 +161,7 @@
    1.12                                                 .append("'] = ")
    1.13                              .append(accessClass(mangledName))
    1.14                 .append(";\n");
    1.15 +            exportedCount++;
    1.16          }
    1.17      }
    1.18  
    1.19 @@ -721,7 +723,7 @@
    1.20          private Extension(Appendable out, Bck2Brwsr.Resources resources,
    1.21              String[] extClassesArray, StringArray explicitlyExported,
    1.22              StringArray asBinary, StringArray classpath
    1.23 -        ) {
    1.24 +        ) throws IOException {
    1.25              super(out, resources, explicitlyExported, asBinary);
    1.26              this.extensionClasses = StringArray.asList(extClassesArray);
    1.27              this.classpath = classpath;
    1.28 @@ -766,6 +768,9 @@
    1.29          @Override
    1.30          protected void generateEpilogue() throws IOException {
    1.31              append("});");
    1.32 +            if (exportedCount == 0) {
    1.33 +                throw new IOException("Creating library without any exported symbols is useless!");
    1.34 +            }
    1.35          }
    1.36  
    1.37          @Override