Oh, I hadn't understood the code sufficiently — there are three possible outcomes here (success, ClassCastException, and NoClassDefFoundError), not just two. Further adjustment made.

But actually I don't really understand the circumstances under which the ClassCastException occurs, is that expected to you @Friendseeker @lrytz?

Oh, I hadn't understood the code sufficiently — there are three possible outcomes here (success, ClassCastException, and NoClassDefFoundError), not just two. Further adjustment made.

But actually I don't really understand the circumstances under which the ClassCastException occurs, is that expected to you @Friendseeker @lrytz?

I don't know either. Only thing I know is that both Scala 2 and Scala 3 compiler checks for NoClassDefFoundError.

Scala 2:

Scala 3:
https://github.com/scala/scala3/blob/d50973b3d3f00080054ff7c08eb9a319c8d1b6de/sbt-bridge/src/dotty/tools/xsbt/CompilerBridgeDriver.java#L144-L157

If we trust the Java documentation, ClassCastException only happens if JVM actually finds the class being casted to, then determines if the cast is invalid.

aha, in the context of the JUnit test that was failing, callback is a scala.tools.xsbt.TestCallback

TestCallback currently extends AnalysisCallback2. if I change it to extend AnalysisCallback3, then:

[error] Missing implementations for 2 members of trait AnalysisCallback3.
[error]   def getSourceInfos(): xsbti.compile.analysis.ReadSourceInfos = ???
[error]   def toVirtualFile(x$1: java.nio.file.Path): xsbti.VirtualFile = ???
[error] class TestCallback extends AnalysisCallback3 {
[error]       ^

@Friendseeker should we push that change through? it appears you did something similar in sbt/zinc#1306, where we see:

-class TestCallback extends AnalysisCallback2 {
+class TestCallback extends AnalysisCallback3 {

aha, in the context of the JUnit test that was failing, callback is a scala.tools.xsbt.TestCallback

TestCallback currently extends AnalysisCallback2. if I change it to extend AnalysisCallback3, then:

[error] Missing implementations for 2 members of trait AnalysisCallback3.

[error]   def getSourceInfos(): xsbti.compile.analysis.ReadSourceInfos = ???

[error]   def toVirtualFile(x$1: java.nio.file.Path): xsbti.VirtualFile = ???

[error] class TestCallback extends AnalysisCallback3 {

[error]       ^

@Friendseeker should we push that change through? it appears you did something similar in sbt/zinc#1306, where we see:

-class TestCallback extends AnalysisCallback2 {

+class TestCallback extends AnalysisCallback3 {

Yes. I definitely think we should push the change in TestCallback to keep things in sync.

labeling "internal" since the problem this fixes never shipped.

heh, I meant to just enable auto-merge once CI liked it, but I apparently fat-fingered that

I already did junit/test locally, but regardless, I will check the Jenkins job and the nightly GitHub Actions jobs before announcing the new release candidate