1 files changed, 48 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/collect/nestedset/CompileOrderExpander.java b/src/main/java/com/google/devtools/build/lib/collect/nestedset/CompileOrderExpander.java
new file mode 100644
index 0000000000..5ac8610438
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/collect/nestedset/CompileOrderExpander.java
@@ -0,0 +1,48 @@
+// 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.lib.collect.nestedset;
+
+import com.google.common.collect.ImmutableCollection;
+
+/**
+ * A nested set expander that implements left-to-right postordering.
+ *
+ * <p>For example, for the nested set {B, D, {A, C}}, the iteration order is "A C B D"
+ * (child-first).
+ *
+ * <p>This type of set would typically be used for artifacts where elements of nested sets go before
+ * the direct members of a set, for example in the case of constructing Java classpaths.
+ */
+final class CompileOrderExpander<E> implements NestedSetExpander<E> {
+
+  // We suppress unchecked warning so that we can access the internal raw structure of the
+  // NestedSet.
+  @SuppressWarnings("unchecked")
+  @Override
+  public void expandInto(NestedSet<E> set, Uniqueifier uniqueifier,
+      ImmutableCollection.Builder<E> builder) {
+    for (NestedSet<E> subset : set.transitiveSets()) {
+      if (!subset.isEmpty() && uniqueifier.isUnique(subset)) {
+        expandInto(subset, uniqueifier, builder);
+      }
+    }
+
+    // This switch is here to compress the memo used by the uniqueifier
+    for (Object e : set.directMembers()) {
+      if (uniqueifier.isUnique(e)) {
+        builder.add((E) e);
+      }
+    }
+  }
+}