Java 16 toolchain support

[davido]

Description of the problem / feature request:

Support for java 16 to be used with toolchain resolution for java rules, e.g. with this section in .bazelrc:

# Builds using remote_jdk16, executes using remote_jdk16 or local_jdk
build:java16 --java_language_version=16
build:java16 --java_runtime_version=16
build:java16 --tool_java_language_version=16
build:java16 --tool_java_runtime_version=16

This build command should fetch remote JDK 16 and produce major java version 16:

  $ bazeldev build --config=java16 gerrit

Feature requests: what underlying problem are you trying to solve with this feature?

Build Java code and produce major java version 16.

According to JDK 16 release schedule: [1] the general availability was announced on 2021/03/16.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

  $ bazel build \
  --java_language_version=16 \
  --java_runtime_version=16 \
  --tool_java_language_version=16 \
  --tool_java_runtime_version=16 \
  gerrit

What operating system are you running Bazel on?

Linux.

What's the output of bazel info release?

Bazel@HEAD, Next major Bazel release (5.x) should include this feature.

Have you found anything relevant by searching the web?

There is a known issue with DumpPlatformClassPath.

[1] https://openjdk.java.net/projects/jdk/16

[davido]

As the workaround, I'm trying to add support for building with JDK16 using remote_java_repository and default_java_toolchain for Gerrit Code Review: [1].

Unfortunately it doesn't work yet:

  $ bazel build --config=java16 java/com/google/gerrit/common:server
  [...]
  xports=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED' ... (remaining 14 argument(s) skipped)
java.lang.IllegalArgumentException: error: invalid source release: 16
	at jdk.compiler/com.sun.tools.javac.main.Arguments.error(Arguments.java:907)
	at jdk.compiler/com.sun.tools.javac.main.Arguments.doProcessArgs(Arguments.java:383)
	at jdk.compiler/com.sun.tools.javac.main.Arguments.processArgs(Arguments.java:347)
	at jdk.compiler/com.sun.tools.javac.main.Arguments.init(Arguments.java:246)
	at jdk.compiler/com.sun.tools.javac.api.JavacTool.getTask(JavacTool.java:185)
	at com.google.devtools.build.buildjar.javac.BlazeJavacMain.compile(BlazeJavacMain.java:114)
	at com.google.devtools.build.buildjar.ReducedClasspathJavaLibraryBuilder.fallback(ReducedClasspathJavaLibraryBuilder.java:103)
	at com.google.devtools.build.buildjar.ReducedClasspathJavaLibraryBuilder.compileSources(ReducedClasspathJavaLibraryBuilder.java:65)
	at com.google.devtools.build.buildjar.SimpleJavaLibraryBuilder.compileJavaLibrary(SimpleJavaLibraryBuilder.java:110)
	at com.google.devtools.build.buildjar.SimpleJavaLibraryBuilder.run(SimpleJavaLibraryBuilder.java:118)
	at com.google.devtools.build.buildjar.BazelJavaBuilder.build(BazelJavaBuilder.java:97)
	at com.google.devtools.build.buildjar.BazelJavaBuilder.parseAndBuild(BazelJavaBuilder.java:77)
	at com.google.devtools.build.lib.worker.WorkRequestHandler.respondToRequest(WorkRequestHandler.java:115)
	at com.google.devtools.build.lib.worker.WorkRequestHandler.lambda$createResponseThread$0(WorkRequestHandler.java:98)
	at java.base/java.lang.Thread.run(Thread.java:831)
Target //java/com/google/gerrit/common:server failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 0.273s, Critical Path: 0.09s
INFO: 7 processes: 7 internal.
FAILED: Build did NOT complete successfully

Even though, the external OpenJDK was fetched as expected:

  $  /home/davido/.cache/bazel/_bazel_davido/5c01f4f713b675540b8b424c5c647f63/external/openjdk_16_linux/bin/java -fullversion
  openjdk full version "16+36"

@comius Any idea, what I am missing?

[1] https://gerrit-review.googlesource.com/c/gerrit/+/301362

[cushon]

what I am missing?

The JDK9_JVM_OPTS include --patch-module= flags which override the JDK's javac with the one from java_tools, which isn't a JDK 16 javac. That vendored javac version is only needed for older JDK versions, JDK 13 and newer include the fixes that are needed by Strict Java Deps.

diff --git a/tools/BUILD b/tools/BUILD
index c5f3691eae..2fb94b3947 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -1,8 +1,8 @@
 load(
     "@bazel_tools//tools/jdk:default_java_toolchain.bzl",
+    "BASE_JDK9_JVM_OPTS",
     "DEFAULT_JAVACOPTS",
     "DEFAULT_TOOLCHAIN_CONFIGURATION",
-    "JDK9_JVM_OPTS",
     "default_java_toolchain",
 )
 load("@rules_java//java:defs.bzl", "java_package_configuration")
@@ -13,7 +13,7 @@ default_java_toolchain(
     name = "toolchain_jdk_16",
     configuration = DEFAULT_TOOLCHAIN_CONFIGURATION,
     java_runtime = "@openjdk_16_linux//:jdk",
-    jvm_opts = JDK9_JVM_OPTS,
+    jvm_opts = BASE_JDK9_JVM_OPTS,
     misc = DEFAULT_JAVACOPTS,
     source_version = "16",
     target_version = "16",

[davido]

@cushon Thanks, it's embarrassing I missed that.

I've updated gerrit CL: [1] and it works as expected. Unfortunately, I still need to patch Bazel with this PR.

[1] https://gerrit-review.googlesource.com/c/gerrit/+/301362

[davido]

As can be seen from the failing coverage test with Java 16 toolchain:

  $ bazeldev test src/test/shell/bazel/bazel_coverage_java_jdk16_toolchain_released_test
  [...]
  java.io.IOException: Error while instrumenting bazel-out/k8-fastbuild/bin/_javac/collatz-lib/libcollatz-lib_classes/com/example/Collatz.class.
	at org.jacoco.core.instr.Instrumenter.instrumentError(Instrumenter.java:170)
	at org.jacoco.core.instr.Instrumenter.instrument(Instrumenter.java:120)
	at org.jacoco.core.instr.Instrumenter.instrument(Instrumenter.java:145)
	at org.jacoco.core.instr.Instrumenter.instrument(Instrumenter.java:165)
	at com.google.devtools.build.buildjar.instrumentation.JacocoInstrumentationProcessor$1.visitFile(JacocoInstrumentationProcessor.java:141)
	at com.google.devtools.build.buildjar.instrumentation.JacocoInstrumentationProcessor$1.visitFile(JacocoInstrumentationProcessor.java:113)
	at java.base/java.nio.file.Files.walkFileTree(Files.java:2804)
	at java.base/java.nio.file.Files.walkFileTree(Files.java:2876)
	at com.google.devtools.build.buildjar.instrumentation.JacocoInstrumentationProcessor.instrumentRecursively(JacocoInstrumentationProcessor.java:111)
	at com.google.devtools.build.buildjar.instrumentation.JacocoInstrumentationProcessor.processRequest(JacocoInstrumentationProcessor.java:85)
	at com.google.devtools.build.buildjar.SimpleJavaLibraryBuilder.buildJar(SimpleJavaLibraryBuilder.java:151)
	at com.google.devtools.build.buildjar.SimpleJavaLibraryBuilder.run(SimpleJavaLibraryBuilder.java:120)
	at com.google.devtools.build.buildjar.BazelJavaBuilder.build(BazelJavaBuilder.java:99)
	at com.google.devtools.build.buildjar.BazelJavaBuilder.parseAndBuild(BazelJavaBuilder.java:79)
	at com.google.devtools.build.buildjar.BazelJavaBuilder.main(BazelJavaBuilder.java:63)
Caused by: java.lang.IllegalArgumentException: Unsupported class file major version 60
	at org.objectweb.asm.ClassReader.<init>(ClassReader.java:196)
	at org.objectweb.asm.ClassReader.<init>(ClassReader.java:177)
	at org.objectweb.asm.ClassReader.<init>(ClassReader.java:163)
	at org.jacoco.core.internal.instr.InstrSupport.classReaderFor(InstrSupport.java:247)
	at org.jacoco.core.instr.Instrumenter.instrument(Instrumenter.java:86)
	at org.jacoco.core.instr.Instrumenter.instrument(Instrumenter.java:118)
	... 13 more

JaCoCo version needs to be bumped to support Java 16.

An actually asm update is needed. Currently is asm 8.0 used in Bazel, but the Java 16 support was only added in ASM_9_0_BETA:

14 July 2020: ASM 9.0 beta (tag ASM_9_0_BETA)
JDK 16 support (sealed classes), new ASM9 api version

[1] https://asm.ow2.io/versions.html