rt.jar (class sbt.internal.inc.DummyVirtualFile) is not supported

[eed3si9n]

steps

• java.lang.RuntimeException: rt.jar (class sbt.internal.inc.DummyVirtualFile) is not supported davidB/scala-maven-plugin#615

problem

[ERROR] ## Exception when compiling 669 sources to /basedir/spark-mine/core/target/scala-2.12/classes
java.lang.RuntimeException: rt.jar (class sbt.internal.inc.DummyVirtualFile) is not supported
scala.sys.package$.error(package.scala:27)
sbt.internal.inc.Locate$.definesClass(Locate.scala:92)
sbt.internal.inc.Locate.definesClass(Locate.scala)
sbt_inc.SbtIncrementalCompiler$1.definesClass(SbtIncrementalCompiler.java:119)
sbt.internal.inc.Locate$.$anonfun$entry$1(Locate.scala:60)
scala.collection.Iterator$$anon$9.next(Iterator.scala:575)
scala.collection.IterableOnceOps.collectFirst(IterableOnce.scala:1079)
scala.collection.IterableOnceOps.collectFirst$(IterableOnce.scala:1071)
scala.collection.AbstractIterator.collectFirst(Iterator.scala:1288)
sbt.internal.inc.Locate$.$anonfun$entry$2(Locate.scala:67)
sbt.internal.inc.LookupImpl.lookupOnClasspath(LookupImpl.scala:51)
sbt.internal.inc.IncrementalCommon$.$anonfun$isLibraryModified$3(IncrementalCommon.scala:764)
sbt.internal.inc.IncrementalCommon$.$anonfun$isLibraryModified$3$adapted(IncrementalCommon.scala:754)
scala.collection.IterableOnceOps.exists(IterableOnce.scala:591)
scala.collection.IterableOnceOps.exists$(IterableOnce.scala:588)
scala.collection.AbstractIterable.exists(Iterable.scala:919)
sbt.internal.inc.IncrementalCommon$.isLibraryChanged$1(IncrementalCommon.scala:754)

expectation

It works.

notes

sbt avoids this bug by working around like sbt/sbt#5522.

[Friendseeker]

While it is easy to just let Locate.definesClass return false when encountering a DummyVirtualFile, I think the root issue is that the semantic of DummyVirtualFile is unclear. Like is DummyVirtualFile supposed to just represent rt.jar or ct.sym? (in this case might as well rename it as JavaRuntimeFile). Or it it supposed to represent any immutable jar file (so maybe Scala library should also be DummyVirtualFile)?

After all rt.jar defines some classes then why should Locate.definesClass always return false for rt.jar?