src/test/java/com/google/devtools/build/lib/skylark/SkylarkAnnotationContractTest.java

// Copyright 2018 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.lib.skylark;

import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
import com.google.devtools.build.lib.skylarkinterface.SkylarkInterfaceUtils;
import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
import com.google.devtools.build.lib.util.Classpath;
import java.lang.reflect.Method;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/**
 * Tests that bazel usages of {@link SkylarkCallable} and {@link SkylarkModule} abide by the
 * contracts specified in their documentation.
 *
 * <p>Tests in this class use the java reflection API.</p>
 *
 * <p>This verification *would* be done via annotation processor, but annotation processors in
 * java don't have access to the full set of information that the java reflection API has.</p>
 */
@RunWith(JUnit4.class)
public class SkylarkAnnotationContractTest {

  // Common prefix of packages in bazel that may have classes that implement or extend a
  // Skylark type.
  private static final String MODULES_PACKAGE_PREFIX = "com/google/devtools/build";

  /**
   * Verifies that every class in bazel that implements or extends a Skylark type has a clearly
   * resolvable type.
   *
   * <p>If this test fails, it indicates the following error scenario:
   *
   * <p>Suppose class A is a subclass of both B and C, where B and C are annotated with
   * @SkylarkModule annotations (and are thus considered "skylark types"). If B is not a
   * subclass of C (nor visa versa), then it's impossible to resolve whether A is of type
   * B or if A is of type C. It's both! The way to resolve this is usually to have A be its own
   * type (annotated with @SkylarkModule), and thus have the explicit type of A be semantically
   * "B and C".
   */
  @Test
  public void testResolvableSkylarkModules() throws Exception {
    for (Class<?> candidateClass : Classpath.findClasses(MODULES_PACKAGE_PREFIX)) {
      SkylarkInterfaceUtils.getSkylarkModule(candidateClass);
    }
  }

  /**
   * Verifies that no class or interface has a method annotated with {@link SkylarkCallable} unless
   * that class or interface is annotated with either {@link SkylarkGlobalLibrary} or with
   * {@link SkylarkModule}.
   */
  @Test
  public void testSkylarkCallableScope() throws Exception {
    for (Class<?> candidateClass : Classpath.findClasses(MODULES_PACKAGE_PREFIX)) {
      if (SkylarkInterfaceUtils.getSkylarkModule(candidateClass) == null
          && !SkylarkInterfaceUtils.hasSkylarkGlobalLibrary(candidateClass)) {
        for (Method method : candidateClass.getMethods()) {
          SkylarkCallable callable = SkylarkInterfaceUtils.getSkylarkCallable(method);
          if (callable != null && method.getDeclaringClass() == candidateClass) {
            throw new AssertionError(String.format(
                "Class %s has a SkylarkCallable method %s but is neither a @SkylarkModule nor a "
                    + "@SkylarkGlobalLibrary",
                candidateClass,
                method.getName()));
          }
        }
      }
    }
  }
}