Add support for callbacks in import annotations.

src/de/inetsoftware/jwebassembly/module/FunctionManager.java

@@ -17,6 +17,7 @@ package de.inetsoftware.jwebassembly.module;
 
 import static de.inetsoftware.jwebassembly.module.WasmCodeBuilder.CLASS_INIT;
 
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
@@ -110,8 +111,17 @@ class FunctionManager {
      * @param importAnannotation
      *            the annotation of the import
      */
-    void markAsImport( @Nonnull FunctionName name, Map<String, Object> importAnannotation ) {
+    void markAsImport( @Nonnull FunctionName name, @Nonnull Map<String, Object> importAnannotation ) {
         markAsImport( name, ( key ) -> importAnannotation.get( key ) );
+
+        // register possible callbacks as needed methods
+        Object callbacks = importAnannotation.get( "callbacks" );
+        if( callbacks != null ) {
+            for( Object callback : (Object[])callbacks ) {
+                name = new FunctionName( (String)callback );
+                markAsExport( name, Collections.emptyMap() );
+            }
+        }
     }
 
     /**
@@ -127,6 +137,19 @@ class FunctionManager {
         getOrCreate( name ).importAnannotation = importAnannotation;
     }
 
+    /**
+     * Mark the function as export function and as needed.
+     * 
+     * @param name
+     *            the function name
+     * @param exportAnannotation
+     *            the annotation of the export
+     */
+    void markAsExport( @Nonnull FunctionName name, @Nonnull Map<String, Object> exportAnannotation ) {
+        markAsNeeded( name, false );
+        getOrCreate( name ).exportAnannotation = exportAnannotation;
+    }
+
     /**
      * Same like markAsNeeded but it will replace the function name if already registered.
      * 
@@ -230,6 +253,17 @@ class FunctionManager {
         return getOrCreate( name ).importAnannotation;
     }
 
+    /**
+     * Get the annotation of an export function
+     * 
+     * @param name
+     *            the function name
+     * @return the annotation or null
+     */
+    Map<String, Object> getExportAnannotation( FunctionName name ) {
+        return getOrCreate( name ).exportAnannotation;
+    }
+
     /**
      * Get the first FunctionName that is required but was not scanned.
      * 
@@ -462,6 +496,7 @@ class FunctionManager {
      * State of a function/method
      */
     private static class FunctionState {
+
         private State                    state     = State.None;
 
         private MethodInfo               method;
@@ -470,6 +505,8 @@ class FunctionManager {
 
         private Function<String, Object> importAnannotation;
 
+        private Map<String, Object>      exportAnannotation;
+
         private int                      vtableIdx = -1;
 
         private int                      itableIdx = -1;

src/de/inetsoftware/jwebassembly/module/ModuleGenerator.java

@@ -519,7 +519,7 @@ public class ModuleGenerator {
                 if( !method.isStatic() ) {
                     throw new WasmException( "Export method must be static: " + name.fullName, -1 );
                 }
-                functions.markAsNeeded( name, false );
+                functions.markAsExport( name, annotationValues );
                 return;
             }
         } catch( Exception ioex ) {
@@ -673,7 +673,7 @@ public class ModuleGenerator {
      *             if any IOException occur
      */
     private void writeExport( FunctionName name, MethodInfo method ) throws IOException {
-        Map<String,Object> export = method.getAnnotation( JWebAssembly.EXPORT_ANNOTATION );
+        Map<String,Object> export = functions.getExportAnannotation( name );
         if( export != null ) {
             String exportName = (String)export.get( "name" );
             if( exportName == null ) {