Second stab at 2.12.4.

[olafurpg]

Last time we upgraded to 2.12.4 the CI failed with a missing shapeless
implicit error from case-app. I can reproduce this error locally only on
the first sbt compile. Running the command the seconds time succeeds
compilation. I want to see if CI fails again, and investigate if
-YdisableFlatCpCaching can fix the error.

EDIT, -YdisableFlatCpCaching did not seem to fix the error. Let me try and remove ArgParserImplicits.

[olafurpg]

cc/ @alexarchambault have you experienced issues resolving case-app/shapeless implicits when upgrading to 2.12.4? The error is

[error] /home/travis/build/scalacenter/scalafix/scalafix-cli/src/main/scala/scalafix/internal/cli/ArgParserImplicits.scala:14: could not find implicit value for parameter parser: caseapp.core.Parser[scalafix.internal.cli.ScalafixOptions]
[error]   val OptionsParser: Parser[ScalafixOptions] = Parser.apply[ScalafixOptions]
[error]                    

Full log: https://travis-ci.org/scalacenter/scalafix/jobs/312965607#L660

Most notably, the cli module compiled fine right before https://travis-ci.org/scalacenter/scalafix/jobs/312965607#L605 but the implicit resolution fails because of custom settings for scripted

    publishLocal := publishLocal
      .dependsOn(
        publishLocal in diff212JVM,
        publishLocal in core212JVM,
        publishLocal in reflect212,
        publishLocal in cli212)
      .value,

It's quite tricky to reproduce locally, but I think I've validated that the error is not caused by scaladoc. My best guess is that it's related to shapeless.Lazy and running concurrent aggregated tasks via sbt. I have never experienced any problems with this before, however, it only started in 2.12.4.

[alexarchambault]

@olafurpg Nothing specific to 2.12.4. But I remember having manually written some Parser in the past, because their derivation was failing for no obvious reason. I haven't investigated more than that…

[olafurpg]

Thanks @alexarchambault

I debugged the issue with -Xlog-implicits and that revealed a stack overflow error

[info]  [E518] scalafix-cli/src/main/scala/scalafix/internal/cli/ArgParserImplicits.scala
[info]         shapeless.this.Strict.mkStrict is not a valid implicit value for shapeless.Strict[caseapp.core.HListParser.Aux[Int with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("stackVerbosity")],Int] :: shapeless.HNil,Option[Int] :: shapeless.HNil,scala.collection.immutable.Nil.type :: shapeless.HNil,None.type :: shapeless.HNil,None.type :: shapeless.HNil,Some[caseapp.Hidden] :: shapeless.HNil,None.type :: shapeless.HNil,PT]] because:
[info]         hasMatchingSymbol reported error: exception during macro expansion:
[info]         java.lang.StackOverflowError
[info]         	at scala.tools.nsc.typechecker.StdAttachments.isMacroImplRef(StdAttachments.scala:153)
[info]         	at scala.tools.nsc.typechecker.StdAttachments.isMacroImplRef$(StdAttachments.scala:153)

I bumped up the stack size in .jvmopts and it seems to have fixed the issue. Someone is catching fatal errors in the compiler 😭

Happy we can at least we can upgrade and 2.12.4 is not to blame 😄