three Travis-CI failures in a row ("object scala.runtime in compiler mirror not found" on sisu-guice JAR)

[Seth Tisue]

seen at e.g. https://travis-ci.org/scala/scala-dist/builds/396107083

[info] Compiling 5 Scala sources to /home/travis/build/scala/scala-dist/project/target/scala-2.10/sbt-0.13/classes...
[error] error while loading <root>, /home/travis/.ivy2/cache/org.sonatype.sisu/sisu-guice/jars/sisu-guice-3.1.0-no_aop.jar (Permission denied)
scala.reflect.internal.MissingRequirementError: object scala.runtime in compiler mirror not found.
	at scala.reflect.internal.MissingRequirementError$.signal(MissingRequirementError.scala:16)
	at scala.reflect.internal.MissingRequirementError$.notFound(MissingRequirementError.scala:17)
	at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:48)
	at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:40)
	at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:61)
	at scala.reflect.internal.Mirrors$RootsBase.getPackage(Mirrors.scala:172)
	at scala.reflect.internal.Mirrors$RootsBase.getRequiredPackage(Mirrors.scala:175)
	at scala.reflect.internal.Definitions$DefinitionsClass.RuntimePackage$lzycompute(Definitions.scala:183)
	at scala.reflect.internal.Definitions$DefinitionsClass.RuntimePackage(Definitions.scala:183)
	at scala.reflect.internal.Definitions$DefinitionsClass.RuntimePackageClass$lzycompute(Definitions.scala:184)
	at scala.reflect.internal.Definitions$DefinitionsClass.RuntimePackageClass(Definitions.scala:184)
	at scala.reflect.internal.Definitions$DefinitionsClass.AnnotationDefaultAttr$lzycompute(Definitions.scala:1024)
	at scala.reflect.internal.Definitions$DefinitionsClass.AnnotationDefaultAttr(Definitions.scala:1023)
	at scala.reflect.internal.Definitions$DefinitionsClass.syntheticCoreClasses$lzycompute(Definitions.scala:1153)
	at scala.reflect.internal.Definitions$DefinitionsClass.syntheticCoreClasses(Definitions.scala:1152)
	at scala.reflect.internal.Definitions$DefinitionsClass.symbolsNotPresentInBytecode$lzycompute(Definitions.scala:1196)
	at scala.reflect.internal.Definitions$DefinitionsClass.symbolsNotPresentInBytecode(Definitions.scala:1196)
	at scala.reflect.internal.Definitions$DefinitionsClass.init(Definitions.scala:1261)
	at scala.tools.nsc.Global$Run.<init>(Global.scala:1290)
	at xsbt.CachedCompiler0$$anon$2.<init>(CompilerInterface.scala:106)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:106)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:95)
	at xsbt.CompilerInterface.run(CompilerInterface.scala:26)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:107)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:53)
	at sbt.compiler.AnalyzingCompiler.compile(AnalyzingCompiler.scala:47)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply$mcV$sp(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler$$anonfun$compileScala$1$1.apply(MixedAnalyzingCompiler.scala:50)
	at sbt.compiler.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:74)
	at sbt.compiler.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:49)
	at sbt.compiler.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:64)
	at sbt.compiler.IC$$anonfun$compileInternal$1.apply(IncrementalCompiler.scala:160)
	at sbt.compiler.IC$$anonfun$compileInternal$1.apply(IncrementalCompiler.scala:160)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:66)
	at sbt.inc.IncrementalCompile$$anonfun$doCompile$1.apply(Compile.scala:64)
	at sbt.inc.IncrementalCommon.cycle(IncrementalCommon.scala:32)
	at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:72)
	at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:71)
	at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:99)
	at sbt.inc.Incremental$.compile(Incremental.scala:71)
	at sbt.inc.IncrementalCompile$.apply(Compile.scala:54)
	at sbt.compiler.IC$.compileInternal(IncrementalCompiler.scala:160)
	at sbt.compiler.IC$.incrementalCompile(IncrementalCompiler.scala:138)
	at sbt.Compiler$.compile(Compiler.scala:155)
	at sbt.Compiler$.compile(Compiler.scala:141)
	at sbt.Defaults$.sbt$Defaults$$compileIncrementalTaskImpl(Defaults.scala:927)
	at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:918)
	at sbt.Defaults$$anonfun$compileIncrementalTask$1.apply(Defaults.scala:916)
	at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
	at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
	at sbt.std.Transform$$anon$4.work(System.scala:63)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
	at sbt.Execute.work(Execute.scala:237)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
	at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159)
	at sbt.CompletionService$$anon$2.call(CompletionService.scala:28)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
[error] (compile:compileIncremental) scala.reflect.internal.MissingRequirementError: object scala.runtime in compiler mirror not found.
Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore?

[Seth Tisue]

I cleared the Travis cache for the 2.13.x branch and re-ran the third failure, and it went green. Not sure what to make of this. Noting for the record in case it recurs.