Inlining code in Scala targets

[gergelyfabian]

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With Scala 2.13.16 if you try inlining code that has been added to your classpath as an ijar/hjar it throws an exception:

error: java.lang.IndexOutOfBoundsException
	at scala.tools.asm.tree.InsnList.get(InsnList.java:94)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$.computeMaxLocalsMaxStack(BackendUtils.scala:728)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$.maxLocals(BackendUtils.scala:636)
	at scala.tools.nsc.backend.jvm.opt.Inliner.inlineCallsite(Inliner.scala:856)
	at scala.tools.nsc.backend.jvm.opt.Inliner.$anonfun$runInliner$10(Inliner.scala:352)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:619)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:617)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:935)
	at scala.collection.IterableOps$WithFilter.foreach(Iterable.scala:905)
	at scala.tools.nsc.backend.jvm.opt.Inliner.runInliner(Inliner.scala:378)
	at scala.tools.nsc.backend.jvm.opt.Inliner.runInlinerAndClosureOptimizer(Inliner.scala:281)
	at scala.tools.nsc.backend.jvm.PostProcessor.runGlobalOptimizations(PostProcessor.scala:156)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$GlobalOptimisingGeneratedClassHandler.complete(GeneratedClassHandler.scala:98)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.$anonfun$run$1(GenBCode.scala:81)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:78)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1564)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1548)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1540)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1674)
	at scala.tools.nsc.Driver.doCompile(Driver.scala:48)
	at scala.tools.nsc.MainClass.doCompile(Main.scala:30)
	at scala.tools.nsc.Driver.process(Driver.scala:68)
	at io.bazel.rulesscala.scalac.ScalacInvoker.invokeCompiler(ScalacInvoker.java:24)
	at io.bazel.rulesscala.scalac.ScalacWorker.compileScalaSources(ScalacWorker.java:272)
	at io.bazel.rulesscala.scalac.ScalacWorker.work(ScalacWorker.java:88)
	at io.bazel.rulesscala.worker.Worker.persistentWorkerMain(Worker.java:96)
	at io.bazel.rulesscala.worker.Worker.workerMain(Worker.java:49)
	at io.bazel.rulesscala.scalac.ScalacWorker.main(ScalacWorker.java:48)
java.lang.IndexOutOfBoundsException
	at scala.tools.asm.tree.InsnList.get(InsnList.java:94)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$.computeMaxLocalsMaxStack(BackendUtils.scala:728)
	at scala.tools.nsc.backend.jvm.analysis.BackendUtils$.maxLocals(BackendUtils.scala:636)
	at scala.tools.nsc.backend.jvm.opt.Inliner.inlineCallsite(Inliner.scala:856)
	at scala.tools.nsc.backend.jvm.opt.Inliner.$anonfun$runInliner$10(Inliner.scala:352)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:619)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:617)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:935)
	at scala.collection.IterableOps$WithFilter.foreach(Iterable.scala:905)
	at scala.tools.nsc.backend.jvm.opt.Inliner.runInliner(Inliner.scala:378)
	at scala.tools.nsc.backend.jvm.opt.Inliner.runInlinerAndClosureOptimizer(Inliner.scala:281)
	at scala.tools.nsc.backend.jvm.PostProcessor.runGlobalOptimizations(PostProcessor.scala:156)
	at scala.tools.nsc.backend.jvm.GeneratedClassHandler$GlobalOptimisingGeneratedClassHandler.complete(GeneratedClassHandler.scala:98)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.$anonfun$run$1(GenBCode.scala:81)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:78)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1564)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1548)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1540)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1674)
	at scala.tools.nsc.Driver.doCompile(Driver.scala:48)
	at scala.tools.nsc.MainClass.doCompile(Main.scala:30)
	at scala.tools.nsc.Driver.process(Driver.scala:68)
	at io.bazel.rulesscala.scalac.ScalacInvoker.invokeCompiler(ScalacInvoker.java:24)
	at io.bazel.rulesscala.scalac.ScalacWorker.compileScalaSources(ScalacWorker.java:272)
	at io.bazel.rulesscala.scalac.ScalacWorker.work(ScalacWorker.java:88)
	at io.bazel.rulesscala.worker.Worker.persistentWorkerMain(Worker.java:96)
	at io.bazel.rulesscala.worker.Worker.workerMain(Worker.java:49)
	at io.bazel.rulesscala.scalac.ScalacWorker.main(ScalacWorker.java:48)

This seems to be a Scala regression since 2.13.9+ and Scala declares that it will fix it in 2.13.17.

Steps to reproduce:

git clone [email protected]:gergelyfabian/bazel-scala-example.git
cd bazel-scala-example
git checkout scala-compiler-bug
bazel build //example-maven:example-maven

Example code:

package mypackage

import com.google.protobuf.CodedOutputStream

object Maven {
  def repro(): Unit = {
    val result = new Array[Byte](0)
    CodedOutputStream.newInstance(result)
  }
}

Using the following scalacopt: -opt-inline-from:**.

---

Once Scala fixes this bug, it will stop inlining code from signature jar files, but you'll get a warning:

$> scq T.scala -cp libcore-hjar.jar:liblite_runtime_only-hjar.jar '-opt:inline:**' -Wopt:_
T.scala:6: warning: com/google/protobuf/CodedOutputStream::newInstance([B)Lcom/google/protobuf/CodedOutputStream; could not be inlined:
Method com/google/protobuf/CodedOutputStream::newInstance([B)Lcom/google/protobuf/CodedOutputStream; cannot be inlined because it does not have any instructions, even though it is not abstract. The class may come from a signature jar file (such as a Bazel 'hjar').
    CodedOutputStream.newInstance(result)
                                 ^
1 warning

---

This behavior is caused by Bazel using hjars/ijars for dependencies.

---

Related Bazel Slack topics:

• https://bazelbuild.slack.com/archives/CA31HN1T3/p1741940032376929
• https://bazelbuild.slack.com/archives/CA31HN1T3/p1741943837077549