Added prohibiting adding of nullability in alternative signatures.

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

@@ -49,6 +49,11 @@ class AlternativeSignatureParsing {
             @Override
             public JetType visitNullableType(JetNullableType nullableType, Void data) {
                 try {
+                    if (!autoType.isNullable()) {
+                        throw new AlternativeSignatureMismatchException(String.format(
+                                "Auto type '%s' is not-null, while type in alternative signature is nullable: '%s'",
+                                DescriptorRenderer.TEXT.renderType(autoType), nullableType.getText()));
+                    }
                     return TypeUtils.makeNullable(computeAlternativeTypeFromAnnotation(nullableType.getInnerType(), autoType));
                 }
                 catch (AlternativeSignatureMismatchException e) {

compiler/testData/readJavaBinaryClass/kotlinSignature/error/AddingNullability.java

@@ -0,0 +1,10 @@
+package test;
+
+import jet.runtime.typeinfo.KotlinSignature;
+
+public class AddingNullability {
+    @KotlinSignature("fun foo() : Int?")
+    public int foo() {
+        throw new UnsupportedOperationException();
+    }
+}

compiler/testData/readJavaBinaryClass/kotlinSignature/error/AddingNullability.kt

@@ -0,0 +1,9 @@
+package test
+
+import java.util.*
+
+public open class AddingNullability : Object() {
+    public open fun foo() : Int {
+        throw UnsupportedOperationException()
+    }
+}

compiler/testData/readJavaBinaryClass/kotlinSignature/error/AddingNullability.txt

@@ -0,0 +1,6 @@
+namespace test
+
+public open class test.AddingNullability : java.lang.Object {
+    public final /*constructor*/ fun <init>(): test.AddingNullability
+    public open fun foo(): jet.Int
+}