Hi,
I came across a very random (low probability) bug using the scalax graph library.

I am attempting to recreate the bug in a simple test case by looping over a test that creates a small cyclic graph and calling graph.isCyclic.

import scalax.collection.Graph
import scalax.collection.edge.Implicits._
import scalax.collection.GraphEdge._

test("cycles") {
(0 until 10000).foreach(_ ⇒ Graph((1 ~+> 2)("a"), (1 ~+> 3)("b"), (2 ~+> 3)("c"), (3 ~+> 4)("d"), (4 ~+> 2)("e")).isCyclic)
}

The relevant code where the stack starts looks like this :

https://github.com/scala-graph/scala-graph/blob/master/core/src/main/scala/scalax/collection/Graph.scala#L43

@transient lazy val isDirected =
edgeT.tpe.baseClasses contains (typeOf[DiHyperEdgeLike[_]].typeSymbol)

Here is the stack

[11:10:56][Step 1/1] java.lang.AssertionError: assertion failed: trait EdgeLike
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.finishSym$1(UnPickler.scala:281)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readSymbol(UnPickler.scala:292)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.run(UnPickler.scala:76)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler.unpickle(UnPickler.scala:37)
[11:10:56][Step 1/1] at scala.reflect.runtime.JavaMirrors$JavaMirror.unpickleClass(JavaMirrors.scala:565)
[11:10:56][Step 1/1] at scala.reflect.runtime.SymbolLoaders$TopClassCompleter.complete(SymbolLoaders.scala:32)
[11:10:56][Step 1/1] at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1231)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.scala$reflect$internal$pickling$UnPickler$Scan$$fromName$1(UnPickler.scala:207)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readExtSymbol$1(UnPickler.scala:226)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readSymbol(UnPickler.scala:250)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readSymbolRef(UnPickler.scala:783)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readType(UnPickler.scala:346)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.at(UnPickler.scala:171)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readTypeRef(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readType$1.apply(UnPickler.scala:353)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readType$1.apply(UnPickler.scala:353)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.PickleBuffer.until(PickleBuffer.scala:163)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.PickleBuffer.until(PickleBuffer.scala:163)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readType(UnPickler.scala:353)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.at(UnPickler.scala:171)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readTypeRef(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readType(UnPickler.scala:358)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$$anonfun$readTypeRef$1.apply(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.at(UnPickler.scala:171)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readTypeRef(UnPickler.scala:792)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readType(UnPickler.scala:366)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$LazyTypeRef$$anonfun$34.apply(UnPickler.scala:855)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$LazyTypeRef$$anonfun$34.apply(UnPickler.scala:855)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.at(UnPickler.scala:171)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan$LazyTypeRef.complete(UnPickler.scala:855)
[11:10:56][Step 1/1] at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1231)
[11:10:56][Step 1/1] at scala.reflect.internal.Symbols$Symbol.initialize(Symbols.scala:1374)
[11:10:56][Step 1/1] at scala.reflect.internal.Symbols$Symbol.annotations(Symbols.scala:1581)
[11:10:56][Step 1/1] at scala.reflect.internal.Symbols$Symbol.addAnnotation(Symbols.scala:1600)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.readSymbolAnnotation(UnPickler.scala:491)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler$Scan.run(UnPickler.scala:88)
[11:10:56][Step 1/1] at scala.reflect.internal.pickling.UnPickler.unpickle(UnPickler.scala:37)
[11:10:56][Step 1/1] at scala.reflect.runtime.JavaMirrors$JavaMirror.unpickleClass(JavaMirrors.scala:565)
[11:10:56][Step 1/1] at scala.reflect.runtime.SymbolLoaders$TopClassCompleter.complete(SymbolLoaders.scala:32)
[11:10:56][Step 1/1] at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1231)
[11:10:56][Step 1/1] at scala.reflect.internal.Types$TypeRef.thisInfo(Types.scala:2407)
[11:10:56][Step 1/1] at scala.reflect.internal.Types$TypeRef.baseClasses(Types.scala:2412)
[11:10:56][Step 1/1] at scalax.collection.GraphLike$class.isDirected(Graph.scala:44)
[11:10:56][Step 1/1] at scalax.collection.immutable.DefaultGraphImpl.isDirected$lzycompute(Graph.scala:41)
[11:10:56][Step 1/1] at scalax.collection.immutable.DefaultGraphImpl.isDirected(Graph.scala:41)