// Copyright 2015 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.java.bazel;
import com.google.common.collect.ImmutableList;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Writer;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.charset.Charset;
import java.util.List;
import java.util.Locale;
import java.util.Set;
import javax.lang.model.SourceVersion;
import javax.tools.DiagnosticListener;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
/**
* Provides a {@link JavaCompiler} that has behavior as similar as possible to the java compiler
* provided by default by Bazel. Replace calls to {@link
* javax.tools.ToolProvider#getSystemJavaCompiler} with calls to {@link
* BazelJavaCompiler#newInstance}.
*
* <p>This class is typically used only from a host build tool or in tests. When using this in
* production, langtools.jar and the bootclasspath jars are deployed as separate jar files within
* the runfiles directory.
*/
public class BazelJavaCompiler {
// The default blessed javac options.
private static final String DEFAULT_BOOTCLASSPATH = JavacBootclasspath.asString();
private static final ImmutableList<String> DEFAULT_JAVACOPTS =
ImmutableList.<String>builder()
.addAll(JavaBuilderConfig.defaultJavacOpts())
// The bootclasspath must be specified both via an invocation option and
// via fileManager.setLocation(PLATFORM_CLASS_PATH), to work around what
// appears to be a bug in jdk[6,8] javac.
.add("-bootclasspath")
.add(DEFAULT_BOOTCLASSPATH)
.build();
private static final Class<? extends JavaCompiler> JAVA_COMPILER_CLASS = getJavaCompilerClass();
private static class LangtoolsClassLoader extends URLClassLoader {
public LangtoolsClassLoader() throws MalformedURLException {
super(
new URL[] {getLangtoolsJar().toURI().toURL()},
// We use the bootstrap classloader (null) as the parent classloader
// instead of the default "system" class loader; we intentionally do
// not consult the classpath. This way the class path is not
// polluted, we reduce the risk of having multiple langtools on the
// classpath, and langtools.jar is only opened if this method is
// called. And this will reduce problems for automated java
// dependency analysis, which other teams are trying to do.
null);
}
}
private static Class<? extends JavaCompiler> getJavaCompilerClass() {
try {
ClassLoader cl = new LangtoolsClassLoader();
return getJavaCompilerClass(cl);
} catch (Exception e) {
throw new RuntimeException("Cannot get java compiler", e);
}
}
private static Class<? extends JavaCompiler> getJavaCompilerClass(ClassLoader cl)
throws Exception {
return Class.forName("com.sun.tools.javac.api.JavacTool", true, cl)
.asSubclass(JavaCompiler.class);
}
/** Returns the langtools jar. */
public static File getLangtoolsJar() {
return JavaLangtools.file();
}
/** Returns the default javacopts, including the blessed bootclasspath. */
public static List<String> getDefaultJavacopts() {
return DEFAULT_JAVACOPTS;
}
/**
* Returns a new {@link JavaCompiler} that has behavior as similar as possible to the java
* compiler provided by default by the bazel build system, independent of the user-specified
* {@code JAVABASE}.
*
* <p>More precisely, this method works analogously to {@link
* javax.tools.ToolProvider#getSystemJavaCompiler}, but returns a {@code JavaCompiler} that
* differs in these details:
*
* <ul>
* <li> uses the blessed javac implementation: {@code //tools/defaults:java_langtools}, as
* defined by bazel's --java_langtools flag.
* <li> uses the blessed boot class path: {@code //tools/defaults:javac_bootclasspath}, as
* defined by bazel's --javac_bootclasspath flag.
* <li> uses the blessed default values for javac options such as {@code -source}
* </ul>
*
* <p>This class ensures that (by default) the {@code -source}, {@code -target} and {@code
* -bootclasspath} flags all agree and specify the same (blessed) JDK version, for language and
* API compatibility.
*
* <p>This method finds the javac implementation using a custom classloader that does not consult
* the user's classpath. This works well, unless the return value is cast to a
* javac-implementation class like {@code JavacTask}, in which case the dreaded classloader error
* "can't cast JavacTaskImpl to JavacTask" raises its ugly head, in which case you should use
* {@link #newInstance(ClassLoader)} instead.
*/
public static JavaCompiler newInstance() {
try {
return newInstance(JAVA_COMPILER_CLASS.getConstructor().newInstance());
} catch (Exception e) {
throw new RuntimeException("Cannot get java compiler", e);
}
}
/**
* Returns a new {@link JavaCompiler} that has behavior as similar as possible to the java
* compiler provided by default by bazel, independent of the user-specified {@code JAVABASE}.
*
* <p>This method has effect identical to {@link #newInstance()} (and that method is generally
* preferred to this one), except that the javac implementation is found via the provided
* classloader instead of defining a custom classloader that knows the standard location of the
* blessed javac implementation.
*
* <p>This method is needed when the return value is cast to a javac-implementation class like
* {@code JavacTask}, to avoid the dreaded multiple classloader error "can't cast JavacTaskImpl to
* JavacTask".
*
* <p>Typically, users should pass {@code ClassLoader.getSystemClassLoader()} as the argument to
* this method.
*/
public static JavaCompiler newInstance(ClassLoader cl) {
try {
return newInstance(getJavaCompilerClass(cl).getConstructor().newInstance());
} catch (Exception e) {
throw new RuntimeException("Cannot get java compiler", e);
}
}
private static JavaCompiler newInstance(final JavaCompiler delegate) {
// We forward most operations to the JavaCompiler implementation in langtools.jar.
return new JavaCompiler() {
@Override
public CompilationTask getTask(
Writer out,
JavaFileManager fileManager,
DiagnosticListener<? super JavaFileObject> diagnosticListener,
Iterable<String> options,
Iterable<String> classes,
Iterable<? extends JavaFileObject> compilationUnits) {
// We prepend bazel's default javacopts to user javacopts,
// so that the user can override them. javac supports this
// "last option wins" style of option override.
ImmutableList.Builder<String> fullOptions = ImmutableList.builder();
fullOptions.addAll(getDefaultJavacopts());
if (options != null) {
fullOptions.addAll(options);
}
return delegate.getTask(
out, fileManager, diagnosticListener, fullOptions.build(), classes, compilationUnits);
}
@Override
public StandardJavaFileManager getStandardFileManager(
DiagnosticListener<? super JavaFileObject> diagnosticListener,
Locale locale,
Charset charset) {
StandardJavaFileManager fileManager =
delegate.getStandardFileManager(diagnosticListener, locale, charset);
try {
fileManager.setLocation(
StandardLocation.PLATFORM_CLASS_PATH, // bootclasspath
JavacBootclasspath.asFiles());
} catch (IOException e) {
// Should never happen, according to javadocs for setLocation
throw new RuntimeException(e);
}
return fileManager;
}
@Override
public int run(InputStream in, OutputStream out, OutputStream err, String... arguments) {
// prepend bazel's default javacopts to user arguments
List<String> args =
ImmutableList.<String>builder().addAll(getDefaultJavacopts()).add(arguments).build();
return delegate.run(in, out, err, args.toArray(new String[0]));
}
@Override
public Set<SourceVersion> getSourceVersions() {
return delegate.getSourceVersions();
}
@Override
public int isSupportedOption(String option) {
return delegate.isSupportedOption(option);
}
};
}
}