[jvm-lang] add ability to traverse super classes

java/java-psi-api/src/com/intellij/lang/jvm/util/JvmHierarchyUtil.java

@@ -0,0 +1,67 @@
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.lang.jvm.util;
+
+import com.intellij.lang.jvm.JvmClass;
+import com.intellij.openapi.progress.ProgressManager;
+import gnu.trove.THashSet;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.ArrayDeque;
+import java.util.Queue;
+import java.util.Set;
+import java.util.function.Function;
+
+import static com.intellij.lang.jvm.util.JvmUtil.resolveClass;
+import static com.intellij.lang.jvm.util.JvmUtil.resolveClasses;
+
+public class JvmHierarchyUtil {
+
+  private JvmHierarchyUtil() {}
+
+  /**
+   * Traverses class tree in BFS order applying the function to each superclass.
+   * <p/>
+   * Notes:
+   * <ul>
+   * <li><i>supers</i> term includes both classes and interfaces</li>
+   * <li>the function will also be applied to the start class</li>
+   * <li>if the function returns non-null result for any class then traversal is stopped and result is returned</li>
+   * <li>the function is applied to each class at most once</li>
+   * <li>unresolvable supertypes are skipped</li>
+   * </ul>
+   *
+   * @param start class to start traversal from
+   * @param <R>   type of the result
+   * @return first non-null result or null
+   */
+  public static <R> R traverseSupers(@NotNull JvmClass start, @NotNull Function<? super JvmClass, R> f) {
+    // TODO implement method returning Stream<JvmClass>
+    final Queue<JvmClass> queue = new ArrayDeque<>();
+    queue.offer(start);
+
+    final Set<JvmClass> visited = new THashSet<>();
+    while (!queue.isEmpty()) {
+      ProgressManager.checkCanceled();
+
+      JvmClass current = queue.remove();
+      if (!visited.add(current)) continue;
+
+      R result = f.apply(current);
+      if (result != null) return result;
+
+      queueSupers(queue, current);
+    }
+
+    return null;
+  }
+
+  private static void queueSupers(@NotNull Queue<JvmClass> queue, @NotNull JvmClass current) {
+    JvmClass superClass = resolveClass(current.getSuperClassType());
+    if (superClass != null) {
+      queue.offer(superClass);
+    }
+    for (JvmClass anInterface : resolveClasses(current.getInterfaceTypes())) {
+      queue.offer(anInterface);
+    }
+  }
+}

java/java-psi-api/src/com/intellij/lang/jvm/util/JvmUtil.java

@@ -0,0 +1,29 @@
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.lang.jvm.util;
+
+import com.intellij.lang.jvm.JvmClass;
+import com.intellij.lang.jvm.JvmTypeDeclaration;
+import com.intellij.lang.jvm.types.JvmReferenceType;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import static com.intellij.util.containers.ContainerUtil.mapNotNull;
+
+class JvmUtil {
+
+  private JvmUtil() {}
+
+  @NotNull
+  static Iterable<JvmClass> resolveClasses(@NotNull JvmReferenceType[] types) {
+    return mapNotNull(types, JvmUtil::resolveClass);
+  }
+
+  @Contract("null -> null")
+  @Nullable
+  static JvmClass resolveClass(@Nullable JvmReferenceType type) {
+    if (type == null) return null;
+    JvmTypeDeclaration resolved = type.resolve();
+    return resolved instanceof JvmClass ? (JvmClass)resolved : null;
+  }
+}