troubleshooting jar loading conflicts in sbt

I get the following error on sbt startup, when two specific sbt plugins are added together to a project in its build definition. One of these sbt plugins is scalikejdbc and the other is my own, and clearly their mutual inclusion in a project's build definition results in this error upon sbt startup:

scala.reflect.internal.Types$TypeError: package macros contains object
and package with same name: blackbox

Clearly, it looks as if each plugin brings along a different version of scala.reflect.macros thus causing this error. I can poke inside the jars of the sbt plugins, and indeed one of them may seem to bring along a scala/reflect/macros/blackbox.class ―

$ jar -tvf scalikejdbc-core_2.10/jars/scalikejdbc-core_2.10-2.4.2.jar | grep black

  0 Sat Jun 11 15:51:10 IDT 2016 scala/reflect/macros/blackbox/    
405 Sat Jun 11 15:51:04 IDT 2016 scala/reflect/macros/blackbox/package$.class    
419 Sat Jun 11 15:51:04 IDT 2016 scala/reflect/macros/blackbox/package.class

― however it's hard to positively conclude what gets loaded by sbt during this early startup phase, in order to figure which versions of this package are involved here and which dependencies bring them along.

Thanks for your suggestions about how to proceed with this investigation!

And just for completeness sake ― I include below the full error given by sbt below only ― but I sincerely doubt it adds any information so you can likely ignore it.

scala.reflect.internal.Types$TypeError: package macros contains object and package with same name: blackbox
one of them needs to be removed from classpath
    at scala.tools.nsc.symtab.SymbolLoaders.enterPackage(SymbolLoaders.scala:66)
    at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader$$anonfun$doComplete$4.apply(SymbolLoaders.scala:244)
    at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader$$anonfun$doComplete$4.apply(SymbolLoaders.scala:243)
    at scala.collection.Iterator$class.foreach(Iterator.scala:727)
    at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
    at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
    at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
    at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader.doComplete(SymbolLoaders.scala:243)
    at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:194)
    at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1231)
    at scala.reflect.internal.pickling.UnPickler$Scan.scala$reflect$internal$pickling$UnPickler$Scan$$fromName$1(UnPickler.scala:207)
    at scala.reflect.internal.pickling.UnPickler$Scan.readExtSymbol$1(UnPickler.scala:226)
    at scala.reflect.internal.pickling.UnPickler$Scan.readSymbol(UnPickler.scala:250)
    at scala.reflect.internal.pickling.UnPickler$Scan.readSymbolRef(UnPickler.scala:783)
    at scala.reflect.internal.pickling.UnPickler$Scan.readType(UnPickler.scala:335)
    at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
    at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
    at scala.reflect.internal.pickling.UnPickler$Scan.at(UnPickler.scala:171)
    at scala.reflect.internal.pickling.UnPickler$Scan.readTypeRef(UnPickler.scala:792)
    at scala.reflect.internal.pickling.UnPickler$Scan.readType(UnPickler.scala:345)
    at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
    at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
    at scala.reflect.internal.pickling.UnPickler$Scan.at(UnPickler.scala:171)
    at scala.reflect.internal.pickling.UnPickler$Scan.readTypeRef(UnPickler.scala:792)
    at scala.reflect.internal.pickling.UnPickler$Scan.readAnnotationInfo(UnPickler.scala:466)
    at scala.reflect.internal.pickling.UnPickler$Scan.readSymbolAnnotation(UnPickler.scala:491)
    at scala.reflect.internal.pickling.UnPickler$Scan.run(UnPickler.scala:88)
    at scala.reflect.internal.pickling.UnPickler.unpickle(UnPickler.scala:37)
    at scala.tools.nsc.symtab.classfile.ClassfileParser.scala$tools$nsc$symtab$classfile$ClassfileParser$$parseAttribute$1(ClassfileParser.scala:908)
    at scala.tools.nsc.symtab.classfile.ClassfileParser.parseAttributes(ClassfileParser.scala:1084)
    at scala.tools.nsc.symtab.classfile.ClassfileParser.parseClass(ClassfileParser.scala:580)
    at scala.tools.nsc.symtab.classfile.ClassfileParser.parse(ClassfileParser.scala:88)
    at scala.tools.nsc.symtab.SymbolLoaders$ClassfileLoader.doComplete(SymbolLoaders.scala:261)
    at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:194)
    at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1231)
    at scala.reflect.internal.SymbolTable.openPackageModule(SymbolTable.scala:244)
    at scala.reflect.internal.SymbolTable.openPackageModule(SymbolTable.scala:300)
    at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader.doComplete(SymbolLoaders.scala:247)
    at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:194)
    at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.load(SymbolLoaders.scala:210)
    at scala.reflect.internal.Symbols$Symbol.typeParams(Symbols.scala:1489)
    at scala.reflect.internal.Types$class.scala$reflect$internal$Types$$isRawIfWithoutArgs(Types.scala:4394)
    at scala.reflect.internal.Types$$anon$11.apply(Types.scala:4416)
    at scala.reflect.internal.Symbols$TermSymbol.scala$reflect$internal$Symbols$TermSymbol$$cook$1(Symbols.scala:2581)
    at scala.reflect.internal.Symbols$TermSymbol.doCookJavaRawInfo(Symbols.scala:2589)
    at scala.reflect.internal.Symbols$Symbol.cookJavaRawInfo(Symbols.scala:1442)
    at scala.tools.nsc.typechecker.Infer$Inferencer.checkAccessible(Infer.scala:384)
    at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$makeAccessible(Typers.scala:605)
    at scala.tools.nsc.typechecker.Typers$Typer.typedIdent$2(Typers.scala:5201)
    at scala.tools.nsc.typechecker.Typers$Typer.typedIdentOrWildcard$1(Typers.scala:5218)
    at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5561)
    at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5642)
    at scala.tools.nsc.typechecker.Typers$Typer.typedQualifier(Typers.scala:5727)
    at scala.tools.nsc.typechecker.Typers$Typer.typedQualifier(Typers.scala:5735)
    at scala.tools.nsc.typechecker.Namers$Namer.importSig(Namers.scala:1357)
    at scala.tools.nsc.typechecker.Namers$Namer.getSig$1(Namers.scala:1460)
    at scala.tools.nsc.typechecker.Namers$Namer.typeSig(Namers.scala:1463)
    at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply$mcV$sp(Namers.scala:728)
    at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply(Namers.scala:727)
    at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply(Namers.scala:727)
    at scala.tools.nsc.typechecker.Namers$Namer.scala$tools$nsc$typechecker$Namers$Namer$$logAndValidate(Namers.scala:1496)
    at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1.apply(Namers.scala:727)
    at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1.apply(Namers.scala:726)
    at scala.tools.nsc.typechecker.Namers$$anon$1.completeImpl(Namers.scala:1611)
    at scala.tools.nsc.typechecker.Namers$LockingTypeCompleter$class.complete(Namers.scala:1619)
    at scala.tools.nsc.typechecker.Namers$$anon$1.complete(Namers.scala:1609)
    at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1231)
    at scala.reflect.internal.Symbols$Symbol.initialize(Symbols.scala:1374)
    at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$typedStat$1(Typers.scala:2912)
    at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$61.apply(Typers.scala:3032)
    at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$61.apply(Typers.scala:3032)
    at scala.collection.immutable.List.loop$1(List.scala:170)
    at scala.collection.immutable.List.mapConserve(List.scala:186)
    at scala.tools.nsc.typechecker.Typers$Typer.typedStats(Typers.scala:3032)
    at scala.tools.nsc.typechecker.Typers$Typer.typedPackageDef$1(Typers.scala:5301)
    at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5587)
    at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5642)
    at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5704)
    at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3.apply(Analyzer.scala:99)
    at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:464)
    at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3$$anonfun$run$1.apply(Analyzer.scala:91)
    at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3$$anonfun$run$1.apply(Analyzer.scala:91)
    at scala.collection.Iterator$class.foreach(Iterator.scala:727)
    at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
    at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3.run(Analyzer.scala:91)
    at sbt.compiler.Eval$$anonfun$compile$1$1.apply$mcV$sp(Eval.scala:177)
    at sbt.compiler.Eval$$anonfun$compile$1$1.apply(Eval.scala:177)
    at sbt.compiler.Eval$$anonfun$compile$1$1.apply(Eval.scala:177)
    at scala.reflect.internal.SymbolTable.atPhase(SymbolTable.scala:207)
    at sbt.compiler.Eval.compile$1(Eval.scala:177)
    at sbt.compiler.Eval.compileAndLoad(Eval.scala:182)
    at sbt.compiler.Eval.evalCommon(Eval.scala:152)
    at sbt.compiler.Eval.evalDefinitions(Eval.scala:122)
    at sbt.EvaluateConfigurations$.evaluateDefinitions(EvaluateConfigurations.scala:271)
    at sbt.EvaluateConfigurations$.evaluateSbtFile(EvaluateConfigurations.scala:109)
    at sbt.Load$.sbt$Load$$loadSettingsFile$1(Load.scala:725)
    at sbt.Load$$anonfun$sbt$Load$$memoLoadSettingsFile$1$1.apply(Load.scala:731)
    at sbt.Load$$anonfun$sbt$Load$$memoLoadSettingsFile$1$1.apply(Load.scala:730)
    at scala.collection.MapLike$class.getOrElse(MapLike.scala:128)
    at scala.collection.AbstractMap.getOrElse(Map.scala:58)
    at sbt.Load$.sbt$Load$$memoLoadSettingsFile$1(Load.scala:730)
    at sbt.Load$$anonfun$loadFiles$1$2.apply(Load.scala:738)
    at sbt.Load$$anonfun$loadFiles$1$2.apply(Load.scala:738)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
    at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
    at scala.collection.AbstractTraversable.map(Traversable.scala:105)
    at sbt.Load$.loadFiles$1(Load.scala:738)
    at sbt.Load$.discoverProjects(Load.scala:749)
    at sbt.Load$.discover$1(Load.scala:555)
    at sbt.Load$.loadTransitive(Load.scala:584)
    at sbt.Load$.loadProjects$1(Load.scala:452)
    at sbt.Load$.loadUnit(Load.scala:456)
    at sbt.Load$$anonfun$18$$anonfun$apply$11.apply(Load.scala:291)
    at sbt.Load$$anonfun$18$$anonfun$apply$11.apply(Load.scala:291)
    at sbt.BuildLoader$$anonfun$componentLoader$1$$anonfun$apply$4$$anonfun$apply$5$$anonfun$apply$6.apply(BuildLoader.scala:91)
    at sbt.BuildLoader$$anonfun$componentLoader$1$$anonfun$apply$4$$anonfun$apply$5$$anonfun$apply$6.apply(BuildLoader.scala:90)
    at sbt.BuildLoader.apply(BuildLoader.scala:140)
    at sbt.Load$.loadAll(Load.scala:344)
    at sbt.Load$.loadURI(Load.scala:299)
    at sbt.Load$.load(Load.scala:295)
    at sbt.Load$.load(Load.scala:286)
    at sbt.Load$.apply(Load.scala:140)
    at sbt.Load$.defaultLoad(Load.scala:36)
    at sbt.BuiltinCommands$.liftedTree1$1(Main.scala:492)
    at sbt.BuiltinCommands$.doLoadProject(Main.scala:492)
    at sbt.BuiltinCommands$$anonfun$loadProjectImpl$2.apply(Main.scala:484)
    at sbt.BuiltinCommands$$anonfun$loadProjectImpl$2.apply(Main.scala:484)
    at sbt.Command$$anonfun$applyEffect$1$$anonfun$apply$2.apply(Command.scala:59)
    at sbt.Command$$anonfun$applyEffect$1$$anonfun$apply$2.apply(Command.scala:59)
    at sbt.Command$$anonfun$applyEffect$2$$anonfun$apply$3.apply(Command.scala:61)
    at sbt.Command$$anonfun$applyEffect$2$$anonfun$apply$3.apply(Command.scala:61)
    at sbt.Command$.process(Command.scala:93)
    at sbt.MainLoop$$anonfun$1$$anonfun$apply$1.apply(MainLoop.scala:96)
    at sbt.MainLoop$$anonfun$1$$anonfun$apply$1.apply(MainLoop.scala:96)
    at sbt.State$$anon$1.process(State.scala:184)
    at sbt.MainLoop$$anonfun$1.apply(MainLoop.scala:96)
    at sbt.MainLoop$$anonfun$1.apply(MainLoop.scala:96)
    at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
    at sbt.MainLoop$.next(MainLoop.scala:96)
    at sbt.MainLoop$.run(MainLoop.scala:89)
    at sbt.MainLoop$$anonfun$runWithNewLog$1.apply(MainLoop.scala:68)
    at sbt.MainLoop$$anonfun$runWithNewLog$1.apply(MainLoop.scala:63)
    at sbt.Using.apply(Using.scala:24)
    at sbt.MainLoop$.runWithNewLog(MainLoop.scala:63)
    at sbt.MainLoop$.runAndClearLast(MainLoop.scala:46)
    at sbt.MainLoop$.runLoggedLoop(MainLoop.scala:30)
    at sbt.MainLoop$.runLogged(MainLoop.scala:22)
    at sbt.StandardMain$.runManaged(Main.scala:54)
    at sbt.xMain.run(Main.scala:29)
    at xsbt.boot.Launch$$anonfun$run$1.apply(Launch.scala:109)
    at xsbt.boot.Launch$.withContextLoader(Launch.scala:128)
    at xsbt.boot.Launch$.run(Launch.scala:109)
    at xsbt.boot.Launch$$anonfun$apply$1.apply(Launch.scala:35)
    at xsbt.boot.Launch$.launch(Launch.scala:117)
    at xsbt.boot.Launch$.apply(Launch.scala:18)
    at xsbt.boot.Boot$.runImpl(Boot.scala:41)
    at xsbt.boot.Boot$.main(Boot.scala:17)
    at xsbt.boot.Boot.main(Boot.scala)
error: error while loading package, class file '/home/user/.sbt/boot/scala-2.10.6/org.scala-sbt/sbt/0.13.11/sbt-0.13.11.jar(sbt/package.class)' is broken
(class java.lang.RuntimeException/error reading Scala signature of package.class: package macros contains object and package with same name: blackbox
one of them needs to be removed from classpath)
sbt.compiler.EvalException: Type error in expression

Copying @jrudolph's comment here:

FWIW giving some advice to someone coming to this issue later on also having problems with plugin classpaths. Try adding scalacOptions ++= Seq("-verbose", "-Ylog-classpath") to project/plugins.sbt. This will print out detailed information when the scala compiler loads classes when compiling the build. This should give a hint from which the jar the conflicting classes came from.