src-subject/src/main/java/com/google/auto/factory/gentest/JavaSourceSubject.java

/*
 * Copyright (C) 2013 Google, 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.google.auto.factory.gentest;

import static com.google.common.base.Charsets.UTF_8;
import static com.google.common.base.Preconditions.checkState;

import java.io.File;
import java.io.IOException;
import java.io.StringWriter;
import java.util.Locale;

import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;

import org.junit.ComparisonFailure;
import org.truth0.FailureStrategy;
import org.truth0.subjects.Subject;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.io.Files;
import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.util.JavacTask;
import com.sun.tools.javac.api.JavacTool;

/**
 * A <a href="https://github.com/truth0/truth">Truth</a> {@link Subject} that evaluates Java source
 * {@linkplain File files} and compares them for equality based on the AST.
 *
 * @author Gregory Kick
 */
public final class JavaSourceSubject extends Subject<JavaSourceSubject, File> {
  private final JavacTool compiler;
  private final StandardJavaFileManager fileManager;

  public JavaSourceSubject(FailureStrategy failureStrategy, File subject) {
    super(failureStrategy, subject);
    this.compiler = (JavacTool) ToolProvider.getSystemJavaCompiler();
    this.fileManager = compiler.getStandardFileManager(null /* default diagnostic listener */,
        Locale.getDefault(), UTF_8);
  }

  public void isEquivalentTo(File other) {
    // TODO(gak): do something with the output
    StringWriter out = new StringWriter();
    JavacTask task = compiler.getTask(out, fileManager,
        null /* default diagnostic listener */, ImmutableSet.<String>of(),
        ImmutableSet.<String>of(),
        fileManager.getJavaFileObjectsFromFiles(ImmutableSet.of(getSubject(), other)));
    try {
      ImmutableList<CompilationUnitTree> compilationUnits =
          ImmutableList.copyOf(task.parse());
      checkState(compilationUnits.size() == 2);
      try {
        compilationUnits.get(0).accept(new EqualityScanner(failureStrategy),
            compilationUnits.get(1));
      } catch (AssertionError e) {
        throw new ComparisonFailure("",
            Files.toString(getSubject(), UTF_8), Files.toString(other, UTF_8));
      }
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }
}