Scala.js 1.4.0 breaks linking of fields with type Nothing

This Scala 3 code compiles and links using ScalaJS 1.3.1 and the latest Dotty nightly build, but fails to link using ScalaJS 1.4.0:

package problem


object Other:
  lazy val a = "hello"
  
  // this line causes linking to fail with ScalaJS 1.4.0, but not with 1.3.1
  lazy val b = ???


object Main:
  val view = Other.a

  def main(args: Array[String]): Unit = ()

Output of Sbt build using ScalaJS 1.4.0 under Windows 10 20H2:

[info] welcome to sbt 1.4.6 (AdoptOpenJDK Java 11.0.9)
[info] loading global plugins from C:\Users\djn\.sbt\1.0\plugins
[info] loading settings for project muve-build from plugins.sbt ...
[info] loading project definition from C:\Git\Muve\project
[info] loading settings for project muve from build.sbt ...
Fetching latest Dotty nightly version...
Latest Dotty nightly build version: 3.0.0-RC1-bin-20210111-0f1d350-NIGHTLY
[info] set current project to ScalaJS Linker Problem (in build file:/C:/Git/Muve/)
[info] sbt server started at local:sbt-server-23257b54281723eb2d64
[info] started sbt server
sbt:ScalaJS Linker Problem> clean
[success] Total time: 0 s, completed 13 Jan 2021, 00:32:35
sbt:ScalaJS Linker Problem> fastLinkJS
[warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.
[info] compiling 1 Scala source to C:\Git\Muve\target\scala-3.0.0-RC1\classes ...
[info] Fast optimizing C:\Git\Muve\target\scala-3.0.0-RC1\scalajs-linker-problem-fastopt
[error] stack trace is suppressed; run last Compile / fastLinkJS for the full output
[error] (Compile / fastLinkJS) java.lang.IllegalArgumentException: cannot generate a zero for NothingType
[error] Total time: 6 s, completed 13 Jan 2021, 00:32:43

Full exception output:

sbt:ScalaJS Linker Problem> last Compile / fastLinkJS
[info] Fast optimizing C:\Git\Muve\target\scala-3.0.0-RC1\scalajs-linker-problem-fastopt
[debug] Linker: Compute reachability: 130613 us
[debug] Linker: Assemble LinkedClasses: 14873 us
[debug] Linker: 189468 us
[debug] Optimizer: Batch mode: true
[debug] Optimizer: Incremental part: 52768 us
[debug] Optimizer: Optimizing 211 methods.
[debug] Optimizer: Optimizer part: 144326 us
[debug] Optimizer: 201273 us
[debug] Refiner: Compute reachability: 17781 us
[debug] Refiner: Assemble LinkedClasses: 2146 us
[debug] Refiner: 103948 us
[debug] Module Splitter: Calculate Dependency Info: 3563 us
[debug] Module Splitter: Analyze Modules: 793 us
[debug] Module Splitter: Assemble Modules: 7452 us
[debug] Module Splitter: 13887 us
[debug] Emitter: Class tree cache stats: reused: 0 -- invalidated: 9
[debug] Emitter: Method tree cache stats: reused: 0 -- invalidated: 11
[error] java.lang.IllegalArgumentException: cannot generate a zero for NothingType
[error]         at org.scalajs.linker.backend.emitter.SJSGen.genZeroOfPrim(SJSGen.scala:79)
[error]         at org.scalajs.linker.backend.emitter.SJSGen.genZeroOf(SJSGen.scala:48)
[error]         at org.scalajs.linker.backend.emitter.ClassEmitter.$anonfun$genFieldDefsOfScalaClass$2(ClassEmitter.scala:407)
[error]         at scala.collection.TraversableLike$WithFilter.$anonfun$map$2(TraversableLike.scala:874)
[error]         at scala.collection.immutable.List.foreach(List.scala:431)
[error]         at scala.collection.TraversableLike$WithFilter.map(TraversableLike.scala:873)
[error]         at org.scalajs.linker.backend.emitter.ClassEmitter.genFieldDefsOfScalaClass(ClassEmitter.scala:401)
[error]         at org.scalajs.linker.backend.emitter.ClassEmitter.$anonfun$genJSConstructorFun$1(ClassEmitter.scala:351)
[error]         at scala.collection.immutable.List.flatMap(List.scala:366)
[error]         at org.scalajs.linker.backend.emitter.ClassEmitter.genJSConstructorFun(ClassEmitter.scala:350)
[error]         at org.scalajs.linker.backend.emitter.ClassEmitter.genES5Constructor(ClassEmitter.scala:225)
[error]         at org.scalajs.linker.backend.emitter.ClassEmitter.genConstructor(ClassEmitter.scala:186)
[error]         at org.scalajs.linker.backend.emitter.Emitter.$anonfun$genClass$10(Emitter.scala:438)
[error]         at org.scalajs.linker.backend.emitter.Emitter$MethodCache.getOrElseUpdate(Emitter.scala:668)
[error]         at org.scalajs.linker.backend.emitter.Emitter.genClass(Emitter.scala:438)
[error]         at org.scalajs.linker.backend.emitter.Emitter.$anonfun$emitOnce$4(Emitter.scala:180)
[error]         at scala.collection.immutable.List.map(List.scala:297)
[error]         at org.scalajs.linker.backend.emitter.Emitter.$anonfun$emitOnce$2(Emitter.scala:180)
[error]         at scala.collection.immutable.List.map(List.scala:293)
[error]         at org.scalajs.linker.backend.emitter.Emitter.$anonfun$emitOnce$1(Emitter.scala:177)
[error]         at org.scalajs.logging.Logger.time(Logger.scala:42)
[error]         at org.scalajs.logging.Logger.time$(Logger.scala:40)
[error]         at org.scalajs.sbtplugin.Loggers$SbtLoggerWrapper.time(Loggers.scala:19)
[error]         at org.scalajs.linker.backend.emitter.Emitter.emitOnce(Emitter.scala:181)
[error]         at org.scalajs.linker.backend.emitter.Emitter.emitAvoidGlobalClash(Emitter.scala:151)
[error]         at org.scalajs.linker.backend.emitter.Emitter.emitInternal(Emitter.scala:127)
[error]         at org.scalajs.linker.backend.emitter.Emitter.emit(Emitter.scala:79)
[error]         at org.scalajs.linker.backend.BasicLinkerBackend.$anonfun$emit$1(BasicLinkerBackend.scala:57)
[error]         at org.scalajs.logging.Logger.time(Logger.scala:42)
[error]         at org.scalajs.logging.Logger.time$(Logger.scala:40)
[error]         at org.scalajs.sbtplugin.Loggers$SbtLoggerWrapper.time(Loggers.scala:19)
[error]         at org.scalajs.linker.backend.BasicLinkerBackend.emit(BasicLinkerBackend.scala:57)
[error]         at org.scalajs.linker.standard.StandardLinkerImpl.$anonfun$link$2(StandardLinkerImpl.scala:47)
[error]         at scala.concurrent.Future.$anonfun$flatMap$1(Future.scala:307)
[error]         at scala.concurrent.impl.Promise.$anonfun$transformWith$1(Promise.scala:41)
[error]         at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:64)
[error]         at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1426)
[error]         at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
[error]         at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
[error]         at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
[error]         at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
[error]         at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
[error] (Compile / fastLinkJS) java.lang.IllegalArgumentException: cannot generate a zero for NothingType

Sbt, JDK, and Dotty versions are shown in the above output. Other relevant files are shown below:

plugins.sbt:

addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.5.1")
addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.4.0")

build.sbt:

enablePlugins(ScalaJSPlugin)

name := "ScalaJS Linker Problem"
scalaVersion := dottyLatestNightlyBuild.get

scalaJSUseMainModuleInitializer := true

[sjrd]

Workaround

Give an appropriate explicit type to the lazy val if its rhs makes it infer as Nothing:

  lazy val b: String = ???

[sjrd]

Thank you for the report!