Unexpected `NullPointerException` in `ScalaInstance.scala`

[jypma]

When trying to run bloop test on an SBT-built mostly-java project (ts-reaktive):

• git clone git@github.com:Tradeshift/ts-reaktive.git
• sbt bloopInstall

  $ bloop test ts-reaktive-actors
  java.lang.NullPointerException
  at bloop.ScalaInstance.supportsHydra(ScalaInstance.scala:78)
  at bloop.data.Project$.$anonfun$fromBytesAndOrigin$1(Project.scala:137)
  at bloop.data.Project$.$anonfun$fromBytesAndOrigin$1$adapted(Project.scala:137)
  at scala.Option.map(Option.scala:230)
  at bloop.data.Project$.fromBytesAndOrigin(Project.scala:137)
  at bloop.engine.BuildLoader$.loadProject(BuildLoader.scala:237)
  [...]

  Apparently the compilerJar field is null in ScalaInstance. The error message could potentially be improved ("couldn't find scala compiler?"), by replacing .orNull in the expression for that field.

However I'm unsure what's really going on, since I do recall having used bloop on Java/SBT projects with previous versions, even having ran JUnit tests...

This is with bloop 1.4.0-RC1.

[jvican]

Thanks for reporting. This is a regression, I'll fix it. /cc @dotta

At the very least this could be a better message

This is not the most friendly way to put that your expectation as a user is a better error message.

[jypma]

Thanks a lot for jumping on this!

This is not the most friendly way to put that your expectation as a user is a better error message.

I apologize if I've offended anyone, that was certainly not my intent. I was expressing expectations of the program, not of any of its creators or contributors. The anthropomorphism obviously was too subtle; again, my apologies for that.

I'll edit the description to the intent is more clear. Thanks for mentioning it.

[jvican]

No worries, no personal offense taken. As a user, I agree with your expectation that NPEs should not leak to the end user. This must be a regression from some of the low level compiler APIs that we use in Bloop.

Could you provide more info about the contents of the configuration file ts-reactive-actors, maybe copy paste it here?

[jypma]

It's open source (MIT license), here is its entire build.sbt, but I can try and copy the relevant details here:

lazy val projectSettings = Seq(
  scalaVersion := "2.12.6",
  crossScalaVersions := Seq("2.12.6"),
  publishMavenStyle := true,
  javacOptions ++= Seq("-source", "1.8"),
  scalacOptions ++= Seq("-target:jvm-1.8"),
  [...]
)

lazy val javaSettings = Seq(
  // This forbids including Scala related libraries into the dependency
  autoScalaLibrary := false,

  // Make this a Java-only project in Eclipse
  EclipseKeys.projectFlavor := EclipseProjectFlavor.Java
)

lazy val `ts-reaktive-actors` = project
  .enablePlugins(ProtobufPlugin)
  .enablePlugins(GitVersioning)
  .settings(commonSettings: _*)
  .settings(javaSettings: _*)
  [...]
  .dependsOn(`ts-reaktive-java`, `ts-reaktive-akka`, `ts-reaktive-testkit` % "test")

I'm guessing the autoScalaLibrary := false may be to blame?

[jvican]

It's a good lead, I'll let you know what I find.

[dotta]

@jvican If this is a regression (as it seems to be), I guess a simple fix is to wrap usage of compilerJar in the supportsHydra impl with an Option. This is how it should have been done already. Happy to push a PR with the change if that helps.