Play Framework is hiding the intial exception - scala

Question

I'm getting this error from Play after implementing a controller. If I throw in a try to catch and println the error, I can see what exception was thrown by my code, but otherwise this information is missing and I get an error relating to files in SBT instead.
What is going on during the handling of my exception that is causing this other exception?
I'm running my application with sbt api/run.
[info] p.c.s.AkkaHttpServer - Listening for HTTP on /[0:0:0:0:0:0:0:0]:9000
(Server started, use Enter to stop and go back to the console...)
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.google.inject.internal.cglib.core.$ReflectUtils$1 (file:/Users/dan/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/inject/guice/4.2.3/guice-4.2.3.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of com.google.inject.internal.cglib.core.$ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
2020-10-15 00:55:32 INFO play.api.http.EnabledFilters Enabled Filters (see <https://www.playframework.com/documentation/latest/Filters>):
play.filters.csrf.CSRFFilter
play.filters.headers.SecurityHeadersFilter
play.filters.hosts.AllowedHostsFilter
play.filters.cors.CORSFilter
2020-10-15 00:55:32 INFO play.api.Play Application started (Dev) (no global state)
2020-10-15 00:55:32 ERROR p.api.http.DefaultHttpErrorHandler Error while handling error
java.lang.ClassCastException: class xsbti.BasicVirtualFileRef cannot be cast to class java.io.File (xsbti.BasicVirtualFileRef is in unnamed module of loader sbt.internal.MetaBuildLoader #6e75aa0d; java.io.File is in module java.base of loader 'bootstrap')
at play.sbt.run.PlayReload$.$anonfun$sourceMap$1(PlayReload.scala:69)
at scala.collection.MapLike$MappedValues.get(MapLike.scala:260)
at play.runsupport.Reloader.$anonfun$findSource$1(Reloader.scala:547)
at scala.Option.flatMap(Option.scala:271)
at play.runsupport.Reloader.findSource(Reloader.scala:546)
at play.core.server.DevServerStart$$anon$1$$anon$2.sourceOf(DevServerStart.scala:171)
at play.core.SourceMapper.$anonfun$sourceFor$1(ApplicationProvider.scala:21)
at play.core.SourceMapper.$anonfun$sourceFor$1$adapted(ApplicationProvider.scala:21)
at scala.collection.ArrayOps$.find$extension(ArrayOps.scala:684)
at play.core.SourceMapper.sourceFor(ApplicationProvider.scala:21)
at play.core.SourceMapper.sourceFor$(ApplicationProvider.scala:20)
at play.core.server.DevServerStart$$anon$1$$anon$2.sourceFor(DevServerStart.scala:169)
at play.api.http.HttpErrorHandlerExceptions$.$anonfun$throwableToUsefulException$1(HttpErrorHandler.scala:358)
at scala.Option.flatMap(Option.scala:283)
at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:358)
at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:261)
at play.filters.cors.AbstractCORSPolicy$$anonfun$1.applyOrElse(AbstractCORSPolicy.scala:128)
at play.filters.cors.AbstractCORSPolicy$$anonfun$1.applyOrElse(AbstractCORSPolicy.scala:126)
at scala.concurrent.impl.Promise$Transformation.run(Promise.scala:453)
at play.api.libs.streams.Execution$trampoline$.execute(Execution.scala:70)
at scala.concurrent.impl.Promise$Transformation.submitWithValue(Promise.scala:392)
at scala.concurrent.impl.Promise$DefaultPromise.submitWithValue(Promise.scala:302)
at scala.concurrent.impl.Promise$DefaultPromise.tryComplete0(Promise.scala:249)
at scala.concurrent.impl.Promise$Transformation.handleFailure(Promise.scala:407)
at scala.concurrent.impl.Promise$Transformation.run(Promise.scala:469)
at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:56)
at akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:93)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:94)
at akka.dispatch.BatchingExecutor$BlockableBatch.run(BatchingExecutor.scala:93)
at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:48)
at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:48)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1016)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1665)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1598)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)

Answer 1

It was an incompatibility between play and sbt, and has been fixed:
https://github.com/playframework/playframework/issues/10486

Answer 2

You end up with this error when an exception happens during handling the server error in the default or custom Play error handler. See play.api.http.HttpErrorHandler.