Added checking for missing return type in alternative signature.

compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/AlternativeSignatureParsing.java

@@ -156,6 +156,26 @@ class AlternativeSignatureParsing {
         return result;
     }
 
+    static JetType computeAlternativeReturnType(@NotNull JetType autoType, @Nullable JetTypeReference altReturnTypeRef)
+            throws AlternativeSignatureMismatchException {
+        JetType altReturnType;
+        if (altReturnTypeRef == null) {
+            if (JetStandardClasses.isUnit(autoType)) {
+                altReturnType = autoType;
+            }
+            else {
+                throw new AlternativeSignatureMismatchException(String.format(
+                        "Return type in alternative signature is missing, while in real signature it is '%s'",
+                        DescriptorRenderer.TEXT.renderType(autoType)));
+            }
+        }
+        else {
+            altReturnType = computeAlternativeTypeFromAnnotation(altReturnTypeRef.getTypeElement(),
+                                                                 autoType);
+        }
+        return altReturnType;
+    }
+
     static JavaDescriptorResolver.ValueParameterDescriptors computeAlternativeValueParameters(
             JavaDescriptorResolver.ValueParameterDescriptors valueParameterDescriptors,
             JetNamedFunction altFunDeclaration) throws AlternativeSignatureMismatchException {

compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/JavaDescriptorResolver.java

@@ -1400,11 +1400,8 @@ public class JavaDescriptorResolver implements DependencyClassByQualifiedNameRes
 
                 ValueParameterDescriptors altValueParameters = AlternativeSignatureParsing
                         .computeAlternativeValueParameters(valueParameterDescriptors, altFunDeclaration);
-                JetTypeReference returnTypeRef = altFunDeclaration.getReturnTypeRef();
-                JetType altReturnType = returnTypeRef != null
-                                        ? AlternativeSignatureParsing.computeAlternativeTypeFromAnnotation(returnTypeRef.getTypeElement(),
-                                                                                                           returnType)
-                                        : returnType;
+                JetType altReturnType = AlternativeSignatureParsing.computeAlternativeReturnType(returnType,
+                                                                                                 altFunDeclaration.getReturnTypeRef());
                 List<TypeParameterDescriptor> altTypeParameters = AlternativeSignatureParsing
                         .computeAlternativeTypeParameters(methodTypeParameters, altFunDeclaration);
                 // if no exceptions were thrown, save alternative data