REPL reports NPE when partially applied function is called in a semicolon delimited statement

[nerush]

Having a function defined in REPL like in example below:

def bar: Int => Int => Int = a => b => a + b

the following statements are evaluated to NPE:

val b = bar(1);b(2)
java.lang.NullPointerException
	at rs$line$2$.<init>(rs$line$2:1)
	at rs$line$2$.<clinit>(rs$line$2)
	at rs$line$2.res0Show(rs$line$2)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at dotty.tools.repl.Rendering.valueOf(Rendering.scala:58)
	at dotty.tools.repl.Rendering.renderVal(Rendering.scala:79)
	at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$8(ReplDriver.scala:269)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at dotty.tools.repl.ReplDriver.displayMembers$1(ReplDriver.scala:269)
	at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$15(ReplDriver.scala:296)
	at scala.Option.map(Option.scala:146)
	at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$13(ReplDriver.scala:294)
	at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
	at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
	at dotty.tools.dotc.core.Phases.atPhase$(Phases.scala:35)
	at dotty.tools.dotc.core.Contexts$Context.atPhase(Contexts.scala:57)
	at dotty.tools.repl.ReplDriver.displayDefinitions(ReplDriver.scala:289)
	at dotty.tools.repl.ReplDriver.$anonfun$compile$2(ReplDriver.scala:226)
	at scala.util.Either.fold(Either.scala:188)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:220)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:190)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:143)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.repl.Main.main(Main.scala)

java.lang.NoClassDefFoundError: Could not initialize class rs$line$2$
	at rs$line$2.bShow(rs$line$2)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at dotty.tools.repl.Rendering.valueOf(Rendering.scala:58)
	at dotty.tools.repl.Rendering.renderVal(Rendering.scala:79)
	at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$8(ReplDriver.scala:269)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at dotty.tools.repl.ReplDriver.displayMembers$1(ReplDriver.scala:269)
	at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$15(ReplDriver.scala:296)
	at scala.Option.map(Option.scala:146)
	at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$13(ReplDriver.scala:294)
	at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
	at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
	at dotty.tools.dotc.core.Phases.atPhase$(Phases.scala:35)
	at dotty.tools.dotc.core.Contexts$Context.atPhase(Contexts.scala:57)
	at dotty.tools.repl.ReplDriver.displayDefinitions(ReplDriver.scala:289)
	at dotty.tools.repl.ReplDriver.$anonfun$compile$2(ReplDriver.scala:226)
	at scala.util.Either.fold(Either.scala:188)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:220)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:190)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:143)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.repl.Main.main(Main.scala)

Will try to figure it out and fix, any tips from main contributors are very welcome.

[allanrenucci]

Can be reproduce by simply running this in the REPL:

scala> val foo = "1"; foo.toInt 
java.lang.NumberFormatException: null
...

[allanrenucci]

The issue is that foo is not yet initialised when calling foo.toInt

[allanrenucci]

Values are evaluated as a side effect of rendering them: https://github.com/lampepfl/dotty/blob/master/compiler/src/dotty/tools/repl/Rendering.scala#L73

[rsoeldner]

@allanrenucci If I understand correct, renderMethod is evaluated before vals

Can you give a hint, how to fix this ?

[allanrenucci]

Methods definitions are not evaluated, they are just pretty printed to the user. Only val definitions are evaluated.

The way I would try to solve this issue, is by looking at the code the REPL generates and see if there is something wrong with it. You should be able to do this by adding some debug code here: https://github.com/lampepfl/dotty/blob/master/compiler/src/dotty/tools/repl/ReplDriver.scala#L221-L226