Change object resolution strategy in TypeHierarchyResolver

Instead of creating a synthetic property descriptor for objects, create a
synthetic class object in it and make it inherit from the object. This way all
of object's members will be accessible via its class object

core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/AbstractClassDescriptor.java

@@ -77,6 +77,10 @@ public abstract class AbstractClassDescriptor implements ClassDescriptor {
     @Nullable
     @Override
     public JetType getClassObjectType() {
+        if (getKind() == ClassKind.OBJECT) {
+            return getDefaultType();
+        }
+
         ClassDescriptor classObject = getClassObjectDescriptor();
         return classObject == null ? null : classObject.getDefaultType();
     }

core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/MutableClassDescriptorLite.java

@@ -221,7 +221,7 @@ public abstract class MutableClassDescriptorLite extends ClassDescriptorBase {
 
                 @Override
                 public ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptorLite classObjectDescriptor) {
-                    if (getKind().isSingleton() || isInner()) {
+                    if (getKind() == ClassKind.CLASS_OBJECT || isInner()) {
                         return ClassObjectStatus.NOT_ALLOWED;
                     }
 

core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/InnerClassesScopeWrapper.java

@@ -20,10 +20,7 @@ import com.google.common.base.Predicate;
 import com.google.common.collect.Collections2;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
-import org.jetbrains.jet.lang.descriptors.ClassDescriptor;
-import org.jetbrains.jet.lang.descriptors.ClassifierDescriptor;
-import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
-import org.jetbrains.jet.lang.descriptors.ReceiverParameterDescriptor;
+import org.jetbrains.jet.lang.descriptors.*;
 import org.jetbrains.jet.lang.resolve.name.LabelName;
 import org.jetbrains.jet.lang.resolve.name.Name;
 
@@ -86,7 +83,7 @@ public class InnerClassesScopeWrapper extends AbstractScopeAdapter {
         return "Classes from " + actualScope;
     }
 
-    private static boolean isClass(DeclarationDescriptor descriptor) {
-        return descriptor instanceof ClassDescriptor && !((ClassDescriptor) descriptor).getKind().isSingleton();
+    private static boolean isClass(@Nullable DeclarationDescriptor descriptor) {
+        return descriptor instanceof ClassDescriptor && ((ClassDescriptor) descriptor).getKind() != ClassKind.ENUM_ENTRY;
     }
 }

core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/WritableScopeImpl.java

@@ -21,7 +21,6 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.TestOnly;
 import org.jetbrains.jet.lang.descriptors.*;
-import org.jetbrains.jet.lang.resolve.DescriptorUtils;
 import org.jetbrains.jet.lang.resolve.name.LabelName;
 import org.jetbrains.jet.lang.resolve.name.Name;
 import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
@@ -310,10 +309,6 @@ public class WritableScopeImpl extends WritableScopeWithImports {
     public void addClassifierDescriptor(@NotNull ClassifierDescriptor classDescriptor) {
         checkMayWrite();
 
-        if (DescriptorUtils.isSingleton(classDescriptor)) {
-            throw new IllegalStateException("must not be object: " + classDescriptor);
-        }
-
         addClassifierAlias(classDescriptor.getName(), classDescriptor);
     }