CompilationRule.java

/*
 * Copyright (C) 2014 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.testing.compile;

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

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.testing.compile.Compilation.Result;

import org.junit.Rule;
import org.junit.rules.TestRule;
import org.junit.runner.Description;
import org.junit.runners.JUnit4;
import org.junit.runners.model.Statement;

import java.util.Set;
import java.util.concurrent.atomic.AtomicReference;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.ProcessingEnvironment;
import javax.annotation.processing.RoundEnvironment;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.TypeElement;
import javax.lang.model.util.Elements;
import javax.lang.model.util.Types;
import javax.tools.ToolProvider;

/**
 * A {@link JUnit4} {@link Rule} that executes tests such that a instances of {@link Elements} and
 * {@link Types} are available during execution.
 *
 * <p>To use this rule in a test, just add the following field: <pre><code>
 *   {@code @Rule} public CompilationRule compilationRule = new CompilationRule();</code></pre>
 *
 * @author Gregory Kick
 */
public final class CompilationRule implements TestRule {
  private Elements elements;
  private Types types;

  @Override
  public Statement apply(final Statement base, Description description) {
    return new Statement() {
      @Override public void evaluate() throws Throwable {
        final AtomicReference<Throwable> thrown = new AtomicReference<Throwable>();
        Result result = Compilation.compile(ToolProvider.getSystemJavaCompiler(),
          ImmutableList.of(new AbstractProcessor() {
          @Override
          public SourceVersion getSupportedSourceVersion() {
            return SourceVersion.latest();
          }

          @Override
          public Set<String> getSupportedAnnotationTypes() {
            return ImmutableSet.of("*");
          }

          @Override
          public synchronized void init(ProcessingEnvironment processingEnv) {
            super.init(processingEnv);
            elements = processingEnv.getElementUtils();
            types = processingEnv.getTypeUtils();
          }

          @Override
          public boolean process(Set<? extends TypeElement> annotations,
              RoundEnvironment roundEnv) {
            // just run the test on the last round after compilation is over
            if (roundEnv.processingOver()) {
              try {
                base.evaluate();
              } catch (Throwable e) {
                thrown.set(e);
              }
            }
            return false;
          }
        }),
        ImmutableSet.<String>of(),
        // just compile _something_
        ImmutableList.of(JavaFileObjects.forSourceLines("Dummy", "final class Dummy {}")));
        checkState(result.successful(), result);
        Throwable t = thrown.get();
        if (t != null) {
          throw t;
        }
      }
    };
  }

  /**
   * Returns the {@link Elements} instance associated with the current execution of the rule.
   *
   * @throws IllegalStateException if this method is invoked outside the execution of the rule.
   */
  public Elements getElements() {
    checkState(elements != null, "Not running within the rule");
    return elements;
  }

  /**
   * Returns the {@link Types} instance associated with the current execution of the rule.
   *
   * @throws IllegalStateException if this method is invoked outside the execution of the rule.
   */
  public Types getTypes() {
    checkState(elements != null, "Not running within the rule");
    return types;
  }
}