1 files changed, 71 insertions, 0 deletions
diff --git a/src/tools/xcode-common/java/com/google/devtools/build/xcode/util/Containing.java b/src/tools/xcode-common/java/com/google/devtools/build/xcode/util/Containing.java
new file mode 100644
index 0000000000..8f2434d28f
--- /dev/null
+++ b/src/tools/xcode-common/java/com/google/devtools/build/xcode/util/Containing.java
@@ -0,0 +1,71 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.xcode.util;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.collect.Multimap;
+
+import java.util.Collection;
+import java.util.Map;
+
+/**
+ * Provides methods that make checking for the presence of an item in a collection type-safe. For
+ * instance, in {@code foo.containsKey(bar)}, where {@code foo} is a {@code Map<K, V>}, {@code bar}
+ * can be a type other than {@code K} and may be {@code null}, in which case the method will just
+ * return false (collections that allow null references may of course return true in the latter
+ * case).
+ * <p>
+ * The methods in this class, such as {@link #key(Map, Object)}, will cause a compiler error if you
+ * use the wrong type and throw a {@link NullPointerException} if you pass {@code null} for the
+ * object whose presence to check. In the case where you want to check for {@code null} in a
+ * collection, add a new method to this class, use the methods in the plain Collections API
+ * (such as {@link Collection#contains(Object)}), or use the {@code Optional} type as the element of
+ * the collection.
+ * <p>
+ * TODO(bazel-team): This class should either be simplified or eliminated when the
+ * CollectionIncompatibleType feature is available:
+ * https://code.google.com/p/error-prone/wiki/CollectionIncompatibleType
+ */
+public class Containing {
+  private Containing() {
+    throw new UnsupportedOperationException("static-only");
+  }
+
+  public static <K> boolean key(Map<K, ?> map, K key) {
+    checkNotNull(key);
+    return map.containsKey(key);
+  }
+
+  public static <K> boolean key(Multimap<K, ?> map, K key) {
+    checkNotNull(key);
+    return map.containsKey(key);
+  }
+
+  public static <E> boolean item(Collection<E> collection, E item) {
+    checkNotNull(item);
+    return collection.contains(item);
+  }
+
+  public static <V> boolean value(Map<?, V> map, V value) {
+    checkNotNull(value);
+    return map.containsValue(value);
+  }
+
+  public static <V> boolean value(Multimap<?, V> map, V value) {
+    checkNotNull(value);
+    return map.containsValue(value);
+  }
+}