Scala 3.0.0-M2环境下Sbt运行测试找不到List类定义如何解决

问题背景 #

在Intellij IDEA Ultimate中基于JDK 16使用sbt搭建Scala项目，build.sbt配置如下：

name := "meteo-france-client"
version := "0.1"
scalaVersion := "3.0.0-M2"
libraryDependencies += "org.scalatest" %% "scalatest" % "3.3.0-SNAP3" % Test

测试代码位于src/scala/test/MainTest.scala，内容如下：

import org.scalatest.funsuite.AnyFunSuite

class MainTest extends AnyFunSuite {
  test("Example") {
    assert(1 == 1)
  }
}

问题现象 #

• 项目主代码可正常编译，但IDE中scalatest导入语句和test方法名标红，提示找不到对应符号
• 执行sbt test命令时抛出如下错误：

[info] compiling 1 Scala source to C:\Users\adrie\OneDrive\Documents\dev\meteo-france-client\target\scala-3.0.0-M2\test-classes ...
[error] ## Exception when compiling 1 sources to C:\Users\adrie\OneDrive\Documents\dev\meteo-france-client\target\scala-3.0.0-M2\test-classes
[error] java.lang.NoClassDefFoundError: scala/collection/immutable/List
[error] xsbt.CachedCompilerImpl.run(CachedCompilerImpl.java:65)
[error] xsbt.CompilerInterface.run(CompilerInterface.java:41)
[error] java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error] java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
[error] java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error] java.base/java.lang.reflect.Method.invoke(Method.java:567)
[error] sbt.internal.inc.AnalyzingCompiler.invoke(AnalyzingCompiler.scala:329)
[error] sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:112)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:192)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:247)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:182)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:163)
[error] sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:163)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:210)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:528)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:528)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:175)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:173)
[error] sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:459)
[error] sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
[error] sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:263)
[error] sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:414)
[error] sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:501)
[error] sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:401)
[error] sbt.internal.inc.Incremental$.apply(Incremental.scala:167)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:528)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:482)
[error] sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
[error] sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[error] sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2357)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2314)
[error] sbt.internal.io.Retry$.apply(Retry.scala:46)
[error] sbt.internal.io.Retry$.apply(Retry.scala:28)
[error] sbt.internal.io.Retry$.apply(Retry.scala:23)
[error] sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2310)
[error] scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error] sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
[error] sbt.std.Transform$$anon$4.work(Transform.scala:68)
[error] sbt.Execute.$anonfun$submit$2(Execute.scala:282)
[error] sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
[error] sbt.Execute.work(Execute.scala:291)
[error] sbt.Execute.$anonfun$submit$1(Execute.scala:282)
[error] sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error] sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
[error] java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
[error] java.base/java.lang.Thread.run(Thread.java:831)
[error]
[error] stack trace is suppressed; run 'last Test / compileIncremental' for the full output
[error] (Test / compileIncremental) java.lang.NoClassDefFoundError: scala/collection/immutable/List
[error] Total time: 0 s, completed 26 nov. 2021, 13:33:34

错误原因 #

你关于Scala 3.0.0-M2移除List类的猜测不成立，scala.collection.immutable.List是Scala核心集合类，所有版本均不会移除该类。
本次错误的根本原因为版本兼容性问题：

• Scala 3.0.0-M2属于早期非正式里程碑版本，本身稳定性不足，与JDK 16、配套的sbt编译器桥接组件、ScalaTest 3.3.0-SNAP3快照版本均存在兼容性冲突
• 测试编译阶段，不同版本依赖的Scala标准库出现类路径冲突，导致编译器无法正确加载核心类定义，抛出类未找到错误
• IDE中标红的原因是IntelliJ IDEA对非稳定的Scala 3里程碑版本支持不完善，加上依赖版本不匹配无法完成正确的符号索引

解决方案 #

1. 将build.sbt中的Scala版本升级为正式稳定版，建议使用3.2.0及以上版本：scalaVersion := "3.2.1"
2. 替换ScalaTest依赖为支持Scala 3的正式稳定版，例如：libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.15" % Test
3. 打开project/build.properties文件，将sbt版本设置为1.7.0及以上，确保对Scala 3和JDK 16的兼容：sbt.version=1.8.2
4. 完成修改后执行sbt clean reload update命令，再在IDEA中重新加载项目，即可解决依赖标红和测试运行报错问题

内容的提问来源于stack exchange，提问作者Karzyfox