Add action to write android_binary and lib R.classes directly

For android_binary rules, we regenerate all of
the R.java of the libraries to get the final
resource IDs. Compiling all of them together can
be slow with the normal JavaBuilder, so add a
specialized class writer.

Example build with many R.java classes:
- R.java -> R.class via JavaBuilder: over 80s
- ErrorProne takes about 40% of that. So turning off
  ErrorProne would be projected to be 48s.
  Some of ErrorProne slowness is from static field
  checks (e.g., on Flag classes), which may look
  up the same Type over and over.

In comparison, if we write our own bytecode with ASM:
- ~16s total
- 4.7s to parse R.txt
- 4.8s to write class files
- 5.8s to copy and compress .jar

TODO: clean up SymbolLoader patching (upstream)

This only creates the action. We will need to
separately wire this up in blaze.

NOTE: This also makes the exising R.txt loading
used by live code multi-threaded, since that is
partly I/O-bound. Something to watch out for
(for flakiness, etc.) once this is submitted.

--
MOS_MIGRATED_REVID=125384467

1 files changed, 56 insertions, 0 deletions

diff --git a/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java b/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java
new file mode 100644
index 0000000000..684e5a5919
--- /dev/null
+++ b/src/tools/android/java/com/google/devtools/build/android/ScopedTemporaryDirectory.java
@@ -0,0 +1,56 @@
+// Copyright 2016 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;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+
+/**
+ * Creates a temporary directory that will be deleted once a scope closes. NOTE: If an error occurs
+ * during deletion, it will just stop rather than try an continue.
+ */
+final class ScopedTemporaryDirectory extends SimpleFileVisitor<Path> implements Closeable {
+
+  private final Path path;
+
+  public ScopedTemporaryDirectory(String prefix) throws IOException {
+    this.path = Files.createTempDirectory(prefix);
+  }
+
+  public Path getPath() {
+    return this.path;
+  }
+
+  @Override
+  public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
+    Files.delete(file);
+    return FileVisitResult.CONTINUE;
+  }
+
+  @Override
+  public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
+    Files.delete(dir);
+    return FileVisitResult.CONTINUE;
+  }
+
+  @Override
+  public void close() throws IOException {
+    Files.walkFileTree(path, this);
+  }
+}