1 files changed, 94 insertions, 0 deletions
diff --git a/java/com/google/devtools/build/android/desugar/io/IndexedInputs.java b/java/com/google/devtools/build/android/desugar/io/IndexedInputs.java
new file mode 100644
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+++ b/java/com/google/devtools/build/android/desugar/io/IndexedInputs.java
@@ -0,0 +1,94 @@
+// Copyright 2017 The Bazel Authors. 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.android.desugar.io;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.collect.ImmutableMap;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.CheckReturnValue;
+import javax.annotation.Nullable;
+
+/**
+ * Opens the given list of input files and compute an index of all classes in them, to avoid
+ * scanning all inputs over and over for each class to load. An indexed inputs can have a parent
+ * that is firstly used when a file name is searched.
+ */
+public class IndexedInputs {
+
+  private final ImmutableMap<String, InputFileProvider> inputFiles;
+
+  /**
+   * Parent {@link IndexedInputs} to use before to search a file name into this {@link
+   * IndexedInputs}.
+   */
+  @Nullable
+  private final IndexedInputs parent;
+
+  /** Index a list of input files without a parent {@link IndexedInputs}. */
+  public IndexedInputs(List<InputFileProvider> inputProviders) {
+    this.parent = null;
+    this.inputFiles = indexInputs(inputProviders);
+  }
+
+  /**
+   * Create a new {@link IndexedInputs} with input files previously indexed and with a parent {@link
+   * IndexedInputs}.
+   */
+  private IndexedInputs(
+      ImmutableMap<String, InputFileProvider> inputFiles, IndexedInputs parentIndexedInputs) {
+    this.parent = parentIndexedInputs;
+    this.inputFiles = inputFiles;
+  }
+
+  /**
+   * Create a new {@link IndexedInputs} with input files already indexed and with a parent {@link
+   * IndexedInputs}.
+   */
+  @CheckReturnValue
+  public IndexedInputs withParent(IndexedInputs parent) {
+    checkState(this.parent == null);
+    return new IndexedInputs(this.inputFiles, parent);
+  }
+
+  @Nullable
+  public InputFileProvider getInputFileProvider(String filename) {
+    checkArgument(filename.endsWith(".class"));
+
+    if (parent != null) {
+      InputFileProvider inputFileProvider = parent.getInputFileProvider(filename);
+      if (inputFileProvider != null) {
+        return inputFileProvider;
+      }
+    }
+
+    return inputFiles.get(filename);
+  }
+
+  private ImmutableMap<String, InputFileProvider> indexInputs(
+      List<InputFileProvider> inputProviders) {
+    Map<String, InputFileProvider> indexedInputs = new HashMap<>();
+    for (InputFileProvider inputProvider : inputProviders) {
+      for (String relativePath : inputProvider) {
+        if (relativePath.endsWith(".class") && !indexedInputs.containsKey(relativePath)) {
+          indexedInputs.put(relativePath, inputProvider);
+        }
+      }
+    }
+    return ImmutableMap.copyOf(indexedInputs);
+  }
+}