DFS: Terminate traversal if node handler returns false

core/descriptors/src/org/jetbrains/jet/lang/resolve/OverridingUtil.java

@@ -540,6 +540,38 @@ public class OverridingUtil {
         );
     }
 
+    public static boolean traverseOverridenDescriptors(
+            @NotNull CallableDescriptor originalDescriptor,
+            @NotNull final Function1<CallableDescriptor, Boolean> handler
+    ) {
+        return DFS.dfs(
+                Collections.singletonList(originalDescriptor),
+                new DFS.Neighbors<CallableDescriptor>() {
+                    @NotNull
+                    @Override
+                    public Iterable<? extends CallableDescriptor> getNeighbors(CallableDescriptor current) {
+                        return current.getOverriddenDescriptors();
+                    }
+                },
+                new DFS.AbstractNodeHandler<CallableDescriptor, Boolean>() {
+                    private boolean result = true;
+
+                    @Override
+                    public boolean beforeChildren(CallableDescriptor current) {
+                        if (!handler.invoke(current)) {
+                            result = false;
+                        }
+                        return result;
+                    }
+
+                    @Override
+                    public Boolean result() {
+                        return result;
+                    }
+                }
+        );
+    }
+
     public interface DescriptorSink {
         void addToScope(@NotNull CallableMemberDescriptor fakeOverride);
 

core/descriptors/src/org/jetbrains/jet/lang/types/DescriptorSubstitutor.java

@@ -147,13 +147,15 @@ public class DescriptorSubstitutor {
                 },
                 new DFS.NodeHandlerWithListResult<JetType, TypeParameterDescriptor>() {
                     @Override
-                    public void beforeChildren(JetType current) {
+                    public boolean beforeChildren(JetType current) {
                         ClassifierDescriptor declarationDescriptor = current.getConstructor().getDeclarationDescriptor();
                         // typeParameters in a list, but it contains very few elements, so it's fine to call contains() on it
                         //noinspection SuspiciousMethodCalls
                         if (typeParameters.contains(declarationDescriptor)) {
                             result.add((TypeParameterDescriptor) declarationDescriptor);
                         }
+
+                        return true;
                     }
                 }
         );

core/descriptors/src/org/jetbrains/jet/lang/types/TypeUtils.java

@@ -634,7 +634,7 @@ public class TypeUtils {
                 },
                 new DFS.NodeHandlerWithListResult<JetType, TypeConstructor>() {
                     @Override
-                    public void beforeChildren(JetType current) {
+                    public boolean beforeChildren(JetType current) {
                         TypeConstructor constructor = current.getConstructor();
 
                         Set<JetType> instances = constructorToAllInstances.get(constructor);
@@ -643,6 +643,8 @@ public class TypeUtils {
                             constructorToAllInstances.put(constructor, instances);
                         }
                         instances.add(current);
+
+                        return true;
                     }
 
                     @Override

core/util.runtime/src/org/jetbrains/jet/utils/DFS.java

@@ -68,10 +68,9 @@ public class DFS {
     }
 
     private static <N> void doDfs(@NotNull N current, @NotNull Neighbors<N> neighbors, @NotNull Visited<N> visited, @NotNull NodeHandler<N, ?> handler) {
-        if (!visited.checkAndMarkVisited(current)) {
+        if (!visited.checkAndMarkVisited(current)) return;
-            return;
+        if (!handler.beforeChildren(current)) return;
-        }
+
-        handler.beforeChildren(current);
         for (N neighbor : neighbors.getNeighbors(current)) {
             doDfs(neighbor, neighbors, visited, handler);
         }
@@ -79,8 +78,8 @@ public class DFS {
     }
 
     public interface NodeHandler<N, R> {
-        @KotlinSignature("fun beforeChildren(current: N): Unit")
+        @KotlinSignature("fun beforeChildren(current: N): Boolean")
-        void beforeChildren(N current);
+        boolean beforeChildren(N current);
 
         @KotlinSignature("fun afterChildren(current: N): Unit")
         void afterChildren(N current);
@@ -100,7 +99,8 @@ public class DFS {
 
     public static abstract class AbstractNodeHandler<N, R> implements NodeHandler<N, R> {
         @Override
-        public void beforeChildren(N current) {
+        public boolean beforeChildren(N current) {
+            return true;
         }
 
         @Override