Implement a build_config generator from #95

Summary:
Simplified the build steps a bit.
Use ProjectFilesystem in GenerateBuildConfigStep, and try-with-resources.
Use System.lineSeparator() for platform independent newlines.
Make field final.
Cleaned up unnecessary getter methods.
Simplified creating buildable/build rule in the unit test.
Fixed styling.

I will follow up with another diff that updates the soy docs.

Test Plan: buck test --all

src/com/facebook/buck/android/BUCK

@@ -31,6 +31,8 @@ RULES_SRCS = [
   'AndroidTransitiveDependencyGraph.java',
   'ApkGenrule.java',
   'ApkGenruleDescription.java',
+  'BuildConfig.java',
+  'BuildConfigDescription.java',
   'ComputeExopackageDepsAbi.java',
   'DexProducedFromJavaLibrary.java',
   'DexRDotJavaStep.java',

src/com/facebook/buck/android/BuildConfig.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2014-present Facebook, Inc.
+ *
+ * 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.facebook.buck.android;
+
+import com.facebook.buck.model.BuildTarget;
+import com.facebook.buck.model.BuildTargets;
+import com.facebook.buck.rules.AbstractBuildable;
+import com.facebook.buck.rules.BuildContext;
+import com.facebook.buck.rules.Buildable;
+import com.facebook.buck.rules.BuildableContext;
+import com.facebook.buck.rules.RuleKey;
+import com.facebook.buck.step.Step;
+import com.facebook.buck.step.fs.MakeCleanDirectoryStep;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * {@link BuildConfig} is a {@link Buildable} that can generate a BuildConfig.java file.
+ * <pre>
+ * build_config(
+ *   name = 'debug_build_config',
+ *   package = 'com.example.package',
+ *   debug = True,
+ * )
+ * </pre>
+ * This will produce a genfile that will be parameterized by the name of the
+ * {@code build_config} rule.
+ * This can be used as a dependency for example
+ * for an android library:
+ * <pre>
+ * android_library(
+ *   name = 'my-app-lib',
+ *   srcs = [':debug_build_config'] + glob(['src/**&#47;*.java']),
+ *   deps = [
+ *     ':debug_build_config',
+ *   ],
+ * )
+ * </pre>
+ */
+public class BuildConfig extends AbstractBuildable {
+
+  private final String appPackage;
+  private final boolean debug;
+  private final Path pathToOutputFile;
+
+  protected BuildConfig(
+      BuildTarget buildTarget,
+      String appPackage,
+      boolean debug) {
+    this.appPackage = Preconditions.checkNotNull(appPackage);
+    this.debug = debug;
+    this.pathToOutputFile = BuildTargets.getGenPath(buildTarget, "__%s__")
+        .resolve("BuildConfig.java");
+  }
+
+  @Override
+  public Collection<Path> getInputsToCompareToOutput() {
+    return ImmutableList.of();
+  }
+
+  @Override
+  public RuleKey.Builder appendDetailsToRuleKey(RuleKey.Builder builder) {
+    return builder
+        .set("package", appPackage)
+        .set("debug", debug);
+  }
+
+  @Override
+  public List<Step> getBuildSteps(BuildContext context, BuildableContext buildableContext)
+      throws IOException {
+    ImmutableList.Builder<Step> steps = ImmutableList.builder();
+
+    steps.add(new MakeCleanDirectoryStep(pathToOutputFile.getParent()));
+    steps.add(new GenerateBuildConfigStep(appPackage, debug, pathToOutputFile));
+
+    buildableContext.recordArtifact(pathToOutputFile);
+    return steps.build();
+  }
+
+  @Override
+  public Path getPathToOutputFile() {
+    return pathToOutputFile;
+  }
+
+}

src/com/facebook/buck/android/BuildConfigDescription.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2014-present Facebook, Inc.
+ *
+ * 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.facebook.buck.android;
+
+import com.facebook.buck.rules.BuildRuleParams;
+import com.facebook.buck.rules.BuildRuleType;
+import com.facebook.buck.rules.ConstructorArg;
+import com.facebook.buck.rules.Description;
+import com.facebook.buck.rules.Hint;
+
+public class BuildConfigDescription implements Description<BuildConfigDescription.Arg> {
+
+  public static final BuildRuleType TYPE = new BuildRuleType("build_config");
+
+  @Override
+  public BuildRuleType getBuildRuleType() {
+    return TYPE;
+  }
+
+  @Override
+  public Arg createUnpopulatedConstructorArg() {
+    return new Arg();
+  }
+
+  @Override
+  public BuildConfig createBuildable(BuildRuleParams params, Arg args) {
+    return new BuildConfig(params.getBuildTarget(), args.appPackage, args.debug);
+  }
+
+  public static class Arg implements ConstructorArg {
+    @Hint(name = "package")
+    public String appPackage;
+    public boolean debug;
+  }
+}

src/com/facebook/buck/android/GenerateBuildConfigStep.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2014-present Facebook, Inc.
+ *
+ * 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.facebook.buck.android;
+
+import com.facebook.buck.step.ExecutionContext;
+import com.facebook.buck.step.Step;
+import com.facebook.buck.util.HumanReadableException;
+import com.facebook.buck.util.ProjectFilesystem;
+import com.google.common.base.Objects;
+import com.google.common.base.Preconditions;
+
+import java.io.IOException;
+import java.nio.file.Path;
+
+public class GenerateBuildConfigStep implements Step {
+
+  private final String configPackage;
+  private final boolean debug;
+  private final Path outBuildConfigPath;
+
+  public GenerateBuildConfigStep(
+      String configPackage,
+      boolean debug,
+      Path outBuildConfigPath) {
+    this.configPackage = Preconditions.checkNotNull(configPackage);
+    this.debug = debug;
+    this.outBuildConfigPath = Preconditions.checkNotNull(outBuildConfigPath);
+    if (outBuildConfigPath.getNameCount() == 0) {
+      throw new HumanReadableException("Output BuildConfig.java filepath is missing");
+    }
+
+  }
+
+  @Override
+  public int execute(ExecutionContext context) {
+    StringBuilder builder = new StringBuilder();
+    builder.append("package ");
+    builder.append(configPackage);
+    builder.append(";\n");
+    builder.append("public final class BuildConfig {\n");
+    builder.append("  public final static boolean DEBUG = ");
+    builder.append(String.valueOf(debug));
+    builder.append(";\n");
+    builder.append("}");
+
+    ProjectFilesystem filesystem = context.getProjectFilesystem();
+    try {
+      filesystem.writeContentsToPath(builder.toString(), outBuildConfigPath);
+    } catch (IOException e) {
+      context.logError(e, "Error writing BuildConfig.java: %s", outBuildConfigPath);
+      return 1;
+    }
+
+    return 0;
+  }
+
+  @Override
+  public String getDescription(ExecutionContext context) {
+    return String.format("generate_build_config %s %s", configPackage, String.valueOf(debug));
+  }
+
+  @Override
+  public String getShortName() {
+    return "generate_build_config";
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (!(obj instanceof GenerateBuildConfigStep)) {
+      return false;
+    }
+
+    GenerateBuildConfigStep that = (GenerateBuildConfigStep) obj;
+    return Objects.equal(this.configPackage, that.configPackage) &&
+        Objects.equal(this.debug, that.debug) &&
+        Objects.equal(this.outBuildConfigPath, that.outBuildConfigPath);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hashCode(
+        configPackage,
+        debug,
+        outBuildConfigPath);
+  }
+}

src/com/facebook/buck/rules/KnownBuildRuleTypes.java

@@ -22,6 +22,7 @@
 import com.facebook.buck.android.AndroidManifestDescription;
 import com.facebook.buck.android.AndroidResourceDescription;
 import com.facebook.buck.android.ApkGenruleDescription;
+import com.facebook.buck.android.BuildConfigDescription;
 import com.facebook.buck.android.GenAidlDescription;
 import com.facebook.buck.android.NdkLibraryDescription;
 import com.facebook.buck.android.PrebuiltNativeLibraryDescription;
@@ -163,6 +164,7 @@ static Builder createBuilder(
     builder.register(new AndroidManifestDescription());
     builder.register(new AndroidResourceDescription());
     builder.register(new ApkGenruleDescription());
+    builder.register(new BuildConfigDescription());
     builder.register(new CppBinaryDescription());
     builder.register(new CppLibraryDescription());
     builder.register(new ExportFileDescription());

test/com/facebook/buck/android/BuildConfigTest.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2014-present Facebook, Inc.
+ *
+ * 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.facebook.buck.android;
+
+import static org.junit.Assert.assertEquals;
+
+import com.facebook.buck.model.BuildTarget;
+import com.facebook.buck.rules.AbstractBuildable;
+import com.facebook.buck.rules.BuildContext;
+import com.facebook.buck.rules.BuildRule;
+import com.facebook.buck.rules.Buildable;
+import com.facebook.buck.rules.FakeBuildRuleParams;
+import com.facebook.buck.rules.FakeBuildableContext;
+import com.facebook.buck.step.Step;
+import com.facebook.buck.util.BuckConstant;
+
+import org.easymock.EasyMock;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.util.List;
+
+/**
+ * Unit test for {@link BuildConfig}.
+ */
+public class BuildConfigTest {
+
+  /**
+   * Tests the following methods:
+   * <ul>
+   *   <li>{@link Buildable#getInputsToCompareToOutput()}
+   *   <li>{@link BuildConfig#getPathToOutputFile()}
+   * </ul>
+   */
+  @Test
+  public void testSimpleObserverMethods() {
+    BuildRule buildRule = createSimpleBuildConfigRule();
+    BuildConfig buildConfigRule = (BuildConfig) buildRule.getBuildable();
+
+    assertEquals(
+        BuckConstant.GEN_PATH.resolve("java/com/example/__build_config__/BuildConfig.java"),
+        buildConfigRule.getPathToOutputFile());
+  }
+
+  @Test
+  public void testBuildInternal() throws IOException {
+    BuildRule buildRule = createSimpleBuildConfigRule();
+    BuildConfig buildConfigRule = (BuildConfig) buildRule.getBuildable();
+
+    // Mock out a BuildContext whose DependencyGraph will be traversed.
+    BuildContext buildContext = EasyMock.createMock(BuildContext.class);
+    EasyMock.replay(buildContext);
+
+    List<Step> steps = buildConfigRule.getBuildSteps(buildContext, new FakeBuildableContext());
+    Step generateBuildConfigStep = steps.get(1);
+    GenerateBuildConfigStep expectedStep = new GenerateBuildConfigStep(
+            /* appPackage */ "com.example",
+            /* debug */ true,
+        BuckConstant.GEN_PATH.resolve("java/com/example/__build_config__/BuildConfig.java"));
+    assertEquals(expectedStep, generateBuildConfigStep);
+  }
+
+  @Test
+  public void testGetTypeMethodOfBuilder() {
+    assertEquals("build_config", BuildConfigDescription.TYPE.getName());
+  }
+
+  private static BuildRule createSimpleBuildConfigRule() {
+    // First, create the BuildConfig object.
+    BuildTarget buildTarget = new BuildTarget("//java/com/example", "build_config");
+    BuildConfig buildConfig = new BuildConfig(
+        buildTarget,
+        /* appPackage */ "com.example",
+        /* debug */ true);
+    return new AbstractBuildable.AnonymousBuildRule(
+        BuildConfigDescription.TYPE,
+        buildConfig,
+        new FakeBuildRuleParams(buildTarget));
+  }
+
+  // TODO(nickpalmer): Add another unit test that passes in a non-trivial DependencyGraph and verify
+  // that the resulting set of libraryManifestPaths is computed correctly.
+}