[macwire 2.5.7][scala 3.1.2][jdk 17.0.3.1+2-LTS-6 (Hotspot)]: Compiler error when generating/compiling `wire` macro.

Start by reproducing the wire calls in ProductionServicesModule with Scala 3.1.2 and JDK 17, focusing on the self-typed ServicesModule setup and the compiler stack trace. Compare the generated macro output with the failing $init$ call; done means the example compiles without the JVM backend assertion and the dependency wiring still works.

I've been working on a new project in Scala 3 and trying the Scala 3 support in Macwire and ran into a blocker.

I have the following:

import com.softwaremill.macwire.*

trait ProductionServicesModule extends ServicesModule { self: ConfigModule with
  PoolsModule with
  DatabasesModule with
  CacheModule with
  DAOModule =>

  // Dependencies
  private lazy val theConfigProvider: ConfigProvider = self.configProvider
  private lazy val theForkJoin: ForkJoinThreadPool = self.forkJoin
  private lazy val theIO: IOThreadPool = self.io
  private lazy val theSystemProvider: ActorSystemProvider = self.systemProvider
  private lazy val theCassandraDatabase: CassandraDatabase = self.cassandra
  private lazy val theAsyncCache: AsyncCache = self.asyncCache
  private lazy val theAssocObsDAO: AssociatedObservationsDAO = self.associatedObservationsDAO
  private lazy val theHistoryDAO: HistoryDAO = self.historyDAO
  private lazy val theObsDAO: ObservationsDAO = self.observationsDAO
  private lazy val theObsTypesDAO: ObservationTypesDAO = self.observationTypesDAO

  // Wired Instances - TODO: Compiler bug - can't get macro working here:
  override lazy val observationsService: ObservationsService = wire[ProductionObservationsService]
  override lazy val observationTypesService: ObservationTypesService = wire[ObservationTypesService]

}

Where the ServicesModule looks like:

trait ServicesModule { self: ConfigModule with
  PoolsModule with
  DatabasesModule with
  CacheModule with
  DAOModule =>

  def observationsService: ObservationsService
  def observationTypesService: ObservationTypesService

}

and the other modules that are in scope from the self-typing look very similar (i.e. ConfigModule, PoolsModule, DatabasesModule, etc.).

Note how I've declared the required dependencies into local scope since macwire in Scala 3 can't yet look up dependencies in parent scope. This seemed to work well for the other modules on which ServicesModule depends, but not in ServicesModule itself evidently.

In ServicesModule, the call to wire breaks with a cryptic compiler bug:

[error] java.lang.AssertionError: assertion failed: 'new' call to non-constructor: $init$
[error] 	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
[error] 	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genApply(BCodeBodyBuilder.scala:725)
[error] 	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:361)
[error] 	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:436)
[error] 	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.emitNormalMethodBody$1(BCodeSkelBuilder.scala:766)
[error] 	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genDefDef(BCodeSkelBuilder.scala:801)
[error] 	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:607)
[error] 	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen$$anonfun$1(BCodeSkelBuilder.scala:615)
[error] 	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] 	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] 	at scala.collection.immutable.List.foreach(List.scala:333)
[error] 	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:615)
[error] 	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:230)
[error] 	at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.visit(GenBCode.scala:259)
[error] 	at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.run(GenBCode.scala:224)
[error] 	at dotty.tools.backend.jvm.GenBCodePipeline.buildAndSendToDisk(GenBCode.scala:559)
[error] 	at dotty.tools.backend.jvm.GenBCodePipeline.run(GenBCode.scala:525)
[error] 	at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:63)
[error] 	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:308)
[error] 	at scala.collection.immutable.List.map(List.scala:246)
[error] 	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:309)
[error] 	at dotty.tools.backend.jvm.GenBCode.runOn(GenBCode.scala:71)
[error] 	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:259)
[error] 	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] 	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] 	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1328)
[error] 	at dotty.tools.dotc.Run.runPhases$1(Run.scala:270)
[error] 	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:278)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
[error] 	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68)
[error] 	at dotty.tools.dotc.Run.compileUnits(Run.scala:287)
[error] 	at dotty.tools.dotc.Run.compileSources(Run.scala:220)
[error] 	at dotty.tools.dotc.Run.compile(Run.scala:204)
[error] 	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
[error] 	at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88)
[error] 	at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
[error] 	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:192)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:247)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:182)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:163)
[error] 	at sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:163)
[error] 	at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:210)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:528)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:528)
[error] 	at sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:177)
[error] 	at sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:175)
[error] 	at sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:461)
[error] 	at sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
[error] 	at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
[error] 	at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
[error] 	at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:263)
[error] 	at sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:416)
[error] 	at sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:503)
[error] 	at sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:403)
[error] 	at sbt.internal.inc.Incremental$.apply(Incremental.scala:169)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:528)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:482)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
[error] 	at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[error] 	at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2366)
[error] 	at sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2316)
[error] 	at sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:30)
[error] 	at sbt.internal.io.Retry$.apply(Retry.scala:46)
[error] 	at sbt.internal.io.Retry$.apply(Retry.scala:28)
[error] 	at sbt.internal.io.Retry$.apply(Retry.scala:23)
[error] 	at sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:30)
[error] 	at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2314)
[error] 	at scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error] 	at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
[error] 	at sbt.std.Transform$$anon$4.work(Transform.scala:68)
[error] 	at sbt.Execute.$anonfun$submit$2(Execute.scala:282)
[error] 	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
[error] 	at sbt.Execute.work(Execute.scala:291)
[error] 	at sbt.Execute.$anonfun$submit$1(Execute.scala:282)
[error] 	at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error] 	at sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
[error] 	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] 	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
[error] 	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] 	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
[error] 	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
[error] 	at java.base/java.lang.Thread.run(Thread.java:833)

Wasn't sure whether the best place to post this was here (since y'all are the experts on your macro generation) or the dotty github... but perhaps you can work with the dotty maintainers if you're able to reproduce - or perhaps you'll know what "-isms" to avoid to fix this error?

I tried making sure each class I was wiring had at least an empty constructor (i.e. class ABC() vs class ABC - although I'm not sure if at compile time the difference matters...) since 'new' call to non-constructor: $init$ kind-of sounds like maybe macwire called new on a companion object or something? No luck though... and that's about where I ran out of ideas.

Kind Regards,
Andy