Weird spurious errors during compilation of Play /

Question

I have a large and moderately complex web application, using the standard Typesafe Stack of Play, Scala and Akka. (I'm in the process of adding scala.js, but this problem predates that.)

A couple of months ago, I upgraded to the current Activator-based version of the world (having fallen behind the times), and that's mostly worked fine. But ever since then, I am semi-frequently getting a weird error when I try to compile:

[Querki] $ compile
[trace] Stack trace suppressed: run last scalajvm/compile:compile for the full output.
[error] (scalajvm/compile:compile) java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt2595416303704565240.class (Access is denied)
[error] Total time: 3 s, completed Sep 2, 2014 3:26:43 PM

Once it starts, it usually keeps recurring until I do a clean recompilation, so it's kind of a pain in the tuchus -- full recompilation of the system takes a while, and this is typically happening a couple of times a day. (OTOH, sometimes it simply stops happening, apparently for no reason.) Restarting Activator does not appear to help.

Anyone have any idea what's going on here? As far as I can tell, the classes.bak folder gets created temporarily during the compile process -- I can see it appear and then disappear again once the compile is finished, regardless of whether it succeeds. It definitely does not exist before the failed compiles start. It appears as if sbt is creating a temp folder in a broken state, or something like that.

If it's relevant, this is running on a Windows 7 box; I am using sbt 0.13.5, scala 2.11.1 and Activator 1.2.10.

ETA: Also conceivably relevant, now that I think of it -- I'm also running GitHub for Windows. I mention this because it's a Java-based app that is clearly doing something to check for changes to the tree periodically. (It auto-refreshes now and then; whether it is scanning the tree for changes or listening a la JNotify, I don't know.)

ETA2: Hah -- finally remembered to print the full log before cleaning. Here's the full stack traceback: I don't know what to make of it, but possibly someone on the sbt side of things can use it:

[Querki] $ compile
[info] Compiling 1 Scala source to C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajs\target\scala-2.11\classes...
[info] Fast optimizing C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes\public\javascripts\querki-client-fastopt.js
[trace] Stack trace suppressed: run last scalajvm/compile:compile for the full output.
[error] (scalajvm/compile:compile) java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt1117112335838311075.class (Access is denied)
[error] Total time: 22 s, completed Sep 5, 2014 3:17:25 PM
[Querki] $ last scalajvm/compile:compile
scalajs/compile:compile
[debug]
[debug] Initial source changes:
[debug]         removed:Set()
[debug]         added: Set()
[debug]         modified: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala)
[debug] Removed products: Set()
[debug] External API changes: API Changes: Set()
[debug] Modified binary dependencies: Set()
[debug] Initial directly invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala)
[debug]
[debug] Sources indirectly invalidated by:
[debug]         product: Set()
[debug]         binary dep: Set()
[debug]         external source: Set()
[debug] All initially invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala)
[info] Compiling 1 Scala source to C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajs\target\scala-2.11\classes...
[debug] Getting compiler-interface from component compiler for Scala 2.11.1
[debug] Getting compiler-interface from component compiler for Scala 2.11.1
[debug] Running cached compiler 1f1ebd37, interfacing (CompilerInterface) with Scala compiler version 2.11.1
[debug] Calling Scala compiler with arguments  (CompilerInterface):
[debug]         -Xplugin:C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-compiler_2.11.1\jars\scalajs-compiler_2.11.1-0.5.4.jar
[debug]         -bootclasspath
[debug]         C:\Program Files\Java\jdk1.6.0_38\jre\lib\resources.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\rt.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\sunrsasign.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\jce.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.6.0_38\jre\lib\modules\jdk.boot.jar;C:\Program Files\Java\jdk1.6.0_38\jre\classes;C:\Users\jducoeur\.ivy2\cache\org.scala-lang\scala-library\jars\scala-library-2.11.1.jar
[debug]         -classpath
[debug]         C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajs\target\scala-2.11\classes;C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-library_2.11\jars\scalajs-library_2.11-0.5.4.jar;C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-dom_sjs0.5_2.11\jars\scalajs-dom_sjs0.5_2.11-0.6.jar;C:\Users\jducoeur\.ivy2\cache\org.scala-lang.modules.scalajs\scalajs-jquery_sjs0.5_2.11\jars\scalajs-jquery_sjs0.5_2.11-0.6.jar;C:\Users\jducoeur\.ivy2\cache\org.webjars\jquery\jars\jquery-1.10.2.jar
[debug] Scala compilation took 6.133828284 s
[debug] New invalidations:
[debug]         Set()
[debug] Initial set of included nodes: Set()
[debug] Previously invalidated, but (transitively) depend on new invalidations:
[debug]         Set()
[debug] All newly invalidated sources after taking into account (previously) recompiled sources:Set()
scalajvm/compile:compile
[debug]
[debug] Initial source changes:
[debug]         removed:Set()
[debug]         added: Set()
[debug]         modified: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala, C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\app\qtext\LineParsers.scala)
[debug] Removed products: Set()
[debug] External API changes: API Changes: Set()
[debug] Modified binary dependencies: Set()
[debug] Initial directly invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala, C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\app\qtext\LineParsers.scala)
[debug]
[debug] Sources indirectly invalidated by:
[debug]         product: Set()
[debug]         binary dep: Set()
[debug]         external source: Set()
[debug] All initially invalidated sources: Set(C:\Users\jducoeur\Documents\GitHub\Querki\querki\scala\src\main\scala\qtexttest\LineParsers.scala, C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\app\qtext\LineParsers.scala)
java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt1117112335838311075.class (Access is denied)
        at java.io.FileOutputStream.open(Native Method)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:194)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:145)
        at sbt.Using$$anonfun$fileOutputChannel$1.apply(Using.scala:82)
        at sbt.Using$$anonfun$fileOutputChannel$1.apply(Using.scala:82)
        at sbt.Using$$anon$2.openImpl(Using.scala:72)
        at sbt.OpenFile$class.open(Using.scala:46)
        at sbt.Using$$anon$2.open(Using.scala:70)
        at sbt.Using$$anon$2.open(Using.scala:70)
        at sbt.Using.apply(Using.scala:24)
        at sbt.IO$$anonfun$copyFile$3.apply(IO.scala:583)
        at sbt.IO$$anonfun$copyFile$3.apply(IO.scala:582)
        at sbt.Using.apply(Using.scala:25)
        at sbt.IO$.copyFile(IO.scala:582)
        at sbt.IO$.move(IO.scala:764)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2.sbt$inc$ClassfileManager$$anonfun$$anon$$move(ClassfileManager.scala:77)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2$$anonfun$delete$3.apply(ClassfileManager.scala:53)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2$$anonfun$delete$3.apply(ClassfileManager.scala:52)
        at scala.collection.immutable.HashSet$HashSet1.foreach(HashSet.scala:153)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
        at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
        at sbt.inc.ClassfileManager$$anonfun$transactional$1$$anon$2.delete(ClassfileManager.scala:52)
        at sbt.inc.Incremental$.prune(Incremental.scala:58)
        at sbt.inc.IncrementalCommon.cycle(Incremental.scala:96)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:38)
        at sbt.inc.Incremental$$anonfun$1.apply(Incremental.scala:37)
        at sbt.inc.Incremental$.manageClassfiles(Incremental.scala:65)
        at sbt.inc.Incremental$.compile(Incremental.scala:37)
        at sbt.inc.IncrementalCompile$.apply(Compile.scala:27)
        at sbt.compiler.AggressiveCompile.compile2(AggressiveCompile.scala:157)
        at sbt.compiler.AggressiveCompile.compile1(AggressiveCompile.scala:71)
        at sbt.compiler.AggressiveCompile.apply(AggressiveCompile.scala:46)
        at sbt.Compiler$.apply(Compiler.scala:75)
        at sbt.Compiler$.apply(Compiler.scala:66)
        at sbt.Defaults$.sbt$Defaults$$compileTaskImpl(Defaults.scala:770)
        at sbt.Defaults$$anonfun$compileTask$1.apply(Defaults.scala:762)
        at sbt.Defaults$$anonfun$compileTask$1.apply(Defaults.scala:762)
        at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
        at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:42)
        at sbt.std.Transform$$anon$4.work(System.scala:64)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
        at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18)
        at sbt.Execute.work(Execute.scala:244)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
        at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:160)
        at sbt.CompletionService$$anon$2.call(CompletionService.scala:30)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)
[error] (scalajvm/compile:compile) java.io.FileNotFoundException: C:\Users\jducoeur\Documents\GitHub\Querki\querki\scalajvm\target\scala-2.11\classes.bak\sbt1117112335838311075.class (Access is denied)
[Querki] $