RuntimeException from REPL predef only after compilation is cached

[ches]

I've just upgraded to 0.7.6 and adapted my predef.sc for changes like interp namespacing, etc.

When I freshly rm -rf ~/.ammonite/cache and run amm, everything compiles and my predef works. Once I quit that REPL instance, it won't start again. Wiping the cache again fixes it, once.

My ~/.ammonite/predef.sc looks like this:

repl.prompt() = "\n> "

// Show compiler warnings
repl.compiler.settings.nowarnings.value = false

// Load utility definitions shared with default scala REPL
try interp.load.exec(ammonite.ops.home/".config"/'scala/"replinit.scala")
catch { case _: Exception => println("=== custom REPL init not loaded! ===") }

And the backtrace on every amm run after the first looks like this:

$ amm
Loading...
Exception in thread "main" java.lang.RuntimeException: Error during Predef:
    at ammonite.runtime.Interpreter$$anonfun$10.apply(Interpreter.scala:138)
    at ammonite.runtime.Interpreter$$anonfun$10.apply(Interpreter.scala:118)
    at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:733)
    at scala.collection.immutable.List.foreach(List.scala:381)
    at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:732)
    at ammonite.runtime.Interpreter.<init>(Interpreter.scala:118)
    at ammonite.repl.Repl.<init>(Repl.scala:43)
    at ammonite.Main.instantiateRepl(Main.scala:61)
    at ammonite.Main.run(Main.scala:107)
    at ammonite.Main$$anonfun$main$1$$anonfun$apply$1.apply(Main.scala:249)
    at ammonite.Main$.ammonite$Main$$ifContinually$1(Main.scala:228)
    at ammonite.Main$$anonfun$main$1.apply(Main.scala:230)
    at ammonite.Main$$anonfun$main$1.apply(Main.scala:230)
    at scala.Option.foreach(Option.scala:257)
    at ammonite.Main$.main(Main.scala:230)
    at ammonite.Main.main(Main.scala)
Caused by: java.lang.NullPointerException
    at ammonite.repl.ReplApiImpl.compiler(ApiImpls.scala:117)
    at ammonite.predef.LoadedPredef$.<init>(LoadedPredef.sc:8)
    at ammonite.predef.LoadedPredef$.<clinit>(LoadedPredef.sc:11)
    at ammonite.predef.LoadedPredef.$main(LoadedPredef.sc)
    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 ammonite.runtime.Evaluator$$anon$1.evalMain(Evaluator.scala:106)
    at ammonite.runtime.Evaluator$$anon$1$$anonfun$evalCachedClassFiles$1$$anonfun$apply$6.apply(Evaluator.scala:172)
    at ammonite.runtime.Evaluator$$anon$1$$anonfun$evalCachedClassFiles$1$$anonfun$apply$6.apply(Evaluator.scala:172)
    at ammonite.util.Res$Success.map(Res.scala:62)
    at ammonite.runtime.Evaluator$$anon$1$$anonfun$evalCachedClassFiles$1.apply(Evaluator.scala:172)
    at ammonite.runtime.Evaluator$$anon$1$$anonfun$evalCachedClassFiles$1.apply(Evaluator.scala:168)
    at ammonite.util.Res$$anonfun$1.apply(Res.scala:33)
    at ammonite.util.Res$$anonfun$1.apply(Res.scala:30)
    at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:157)
    at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:157)
    at scala.collection.Iterator$class.foreach(Iterator.scala:893)
    at scala.collection.AbstractIterator.foreach(Iterator.scala:1336)
    at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
    at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
    at scala.collection.TraversableOnce$class.foldLeft(TraversableOnce.scala:157)
    at scala.collection.AbstractTraversable.foldLeft(Traversable.scala:104)
    at ammonite.util.Res$.map(Res.scala:30)
    at ammonite.runtime.Evaluator$$anon$1.evalCachedClassFiles(Evaluator.scala:168)
    at ammonite.runtime.Interpreter.processModule(Interpreter.scala:400)
    at ammonite.runtime.Interpreter$$anonfun$10.apply(Interpreter.scala:121)
    ... 15 more

[lihaoyi]

Ah, yeah, the "don't initialize compiler until needed" logic probably made this break.

The solution would be to add a call to

if (interp.compiler == null) interp.init()

Into this function:

• https://github.com/lihaoyi/Ammonite/blob/d19e8b9887a9ee23f834230c546e7d51d14a5675/amm/repl/src/main/scala/ammonite/repl/ApiImpls.scala#L117

@ches if you have time, check out the repo and see if this fixes your problem. If it works send a PR 😄

[lihaoyi]

A better solution would be to make interp.compiler a Future[() => Global] instead of just a Global; that would let people do

for(c <- interp.compiler) c().settings.nowarnings.value = ...

That would make our compiler-setup code properly trigger the first time the compiler gets initialized, without forcing initialisation of the compiler when not necessary. The Future[() => Global] type would accurately represent the fact that you could get back a different compiler each time, but cannot get one at all until the compiler is initialised for the first time and the Future completes

[ches]

The first fix you suggested did solve the issue. I started to look around for whether there are tests around this area of code but I have essentially no familiarity with the codebase and running the full suite was proving to be an exercise in patience, I roamed off to other things 😅

I'll take another look at your second suggestion when I can devote some time to really understanding what I'm doing in there…

[lihaoyi]

Fixed by c6a282d

[lihaoyi]

http://www.lihaoyi.com/Ammonite/#0.9.0 is out