jmh rules uses jmh hook that doesn't support Java 8 bytecode

[gkossakowski]

While upgrading the rules to Scala 2.12, we've run into mysterious:

ERROR: /Users/gkk/stripe/rules_scala/test/jmh/BUILD:23:1: Couldn't build file test/jmh/test_benchmark_codegen.srcjar: Generating benchmark code for //test/jmh:test_benchmark_codegen failed (Exit 1).
Exception in thread "main" java.lang.RuntimeException
	at org.objectweb.asm.MethodVisitor.visitParameter(Unknown Source)
	at org.objectweb.asm.ClassReader.b(Unknown Source)
	at org.objectweb.asm.ClassReader.accept(Unknown Source)
	at org.objectweb.asm.ClassReader.accept(Unknown Source)
	at org.openjdk.jmh.generators.asm.ASMGeneratorSource.processClass(ASMGeneratorSource.java:60)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.$anonfun$generateJmhBenchmark$3(BenchmarkGenerator.scala:140)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.$anonfun$generateJmhBenchmark$3$adapted(BenchmarkGenerator.scala:139)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.$anonfun$generateJmhBenchmark$2(BenchmarkGenerator.scala:139)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.withClassLoader(BenchmarkGenerator.scala:97)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.$anonfun$generateJmhBenchmark$1(BenchmarkGenerator.scala:134)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.$anonfun$generateJmhBenchmark$1$adapted(BenchmarkGenerator.scala:127)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.withTempDirectory(BenchmarkGenerator.scala:107)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.generateJmhBenchmark(BenchmarkGenerator.scala:127)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator$.main(BenchmarkGenerator.scala:43)
	at io.bazel.rules_scala.jmh_support.BenchmarkGenerator.main(BenchmarkGenerator.scala)

I traced this problem and it's unrelated to Scala 2.12 but related to Java 8 bytecode support. The culpirt is this place: http://hg.openjdk.java.net/code-tools/jmh/file/1ddf31f810a3/jmh-generator-asm/src/main/java/org/openjdk/jmh/generators/asm/ASMClassInfo.java#l65
(called indirectly from BenchmarkGenerator)

asm-based generator in jmh has ASM4 level of bytecode support hardcoded in it which means it supports bytecode up to Java 7. It doesn't look like there's a way to pass a newer version as a parameter so I suspect this code is not widely used.

For comparison, sbt-jmh is calling a different generator in asm: https://github.com/ktoso/sbt-jmh/blob/master/plugin/src/main/scala/pl/project13/scala/sbt/JmhPlugin.scala#L125