test nullable return types are read from .class files

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

@@ -479,7 +479,7 @@ public class JavaDescriptorResolver {
                 DescriptorUtils.getExpectedThisObjectIfNeeded(classDescriptor),
                 typeParameters,
                 semanticServices.getDescriptorResolver().resolveParameterDescriptors(functionDescriptorImpl, parameters),
-                semanticServices.getTypeTransformer().transformToType(returnType),
+                semanticServices.getDescriptorResolver().makeReturnType(returnType, method),
                 Modality.convertFromFlags(method.hasModifierProperty(PsiModifier.ABSTRACT), !method.hasModifierProperty(PsiModifier.FINAL)),
                 resolveVisibilityFromPsiModifiers(method)
         );
@@ -491,6 +491,30 @@ public class JavaDescriptorResolver {
         return substitutedFunctionDescriptor;
     }
 
+    private JetType makeReturnType(PsiType returnType, PsiMethod method) {
+        boolean changeNullable = false;
+        boolean nullable = true;
+
+        for (PsiAnnotation annotation : method.getModifierList().getAnnotations()) {
+            if (annotation.getQualifiedName().equals("jet.typeinfo.JetMethod")) {
+                PsiLiteralExpression nullableExpression = (PsiLiteralExpression) annotation.findAttributeValue("nullableReturnType");
+                if (nullableExpression != null) {
+                    nullable = (Boolean) nullableExpression.getValue();
+                } else {
+                    // default value of parameter
+                    nullable = false;
+                    changeNullable = true;
+                }
+            }
+        }
+        JetType transformedType = semanticServices.getTypeTransformer().transformToType(returnType);
+        if (changeNullable) {
+            return TypeUtils.makeNullableAsSpecified(transformedType, nullable);
+        } else {
+            return transformedType;
+        }
+    }
+
     private static Visibility resolveVisibilityFromPsiModifiers(PsiModifierListOwner modifierListOwner) {
         //TODO report error
         return modifierListOwner.hasModifierProperty(PsiModifier.PUBLIC) ? Visibility.PUBLIC :

compiler/testData/readClass/ReturnTypeNotNull.kt

@@ -0,0 +1,3 @@
+namespace test
+
+fun ff(): String = ""

compiler/testData/readClass/ReturnTypeNullable.kt

@@ -0,0 +1,3 @@
+namespace test
+
+fun ff(): String? = ""

compiler/tests/org/jetbrains/jet/ReadClassDataTest.java

@@ -105,8 +105,6 @@ public class ReadClassDataTest extends UsefulTestCase {
 
     @Override
     public void runTest() throws Exception {
-        if (true) return;
-
         createMockCoreEnvironment();
 
         LanguageASTFactory.INSTANCE.addExplicitExtension(JavaLanguage.INSTANCE, new JavaASTFactory());
@@ -184,7 +182,8 @@ public class ReadClassDataTest extends UsefulTestCase {
         for (int i = 0; i < a.getValueParameters().size(); ++i) {
             compareAnything(ValueParameterDescriptor.class, a.getValueParameters().get(i), b.getValueParameters().get(i));
         }
-        System.out.println("function " + a.getName());
+        Assert.assertEquals(a.getReturnType(), b.getReturnType());
+        System.out.println("fun " + a.getName() + "(...): " + a.getReturnType());
     }
 
     private <T> void compareAnything(Class<T> clazz, T a, T b) {