allow cycles in graphs even when printing with AsciiTreeLayout, fixes #77

src/main/scala/net/virtualvoid/sbt/graph/util/AsciiTreeLayout.scala

@@ -28,20 +28,27 @@ object AsciiTreeLayout {
         }) +
         s.slice(at + 1, s.length)
       else s
-		def toAsciiLines(node: A, level: Int): Vector[String] = {
+		def toAsciiLines(node: A, level: Int, parents: Set[A]): Vector[String] =
-			val line = limitLine((twoSpaces * level) + (if (level == 0) "" else "+-") + display(node))
+			if (parents contains node) // cycle
-			val cs = Vector(children(node): _*)
+				Vector(limitLine((twoSpaces * level) + "#-" + display(node)))
-			val childLines = cs map {toAsciiLines(_, level + 1)}
+			else {
-			val withBar = childLines.zipWithIndex flatMap {
+				val line = limitLine((twoSpaces * level) + (if (level == 0) "" else "+-") + display(node))
-				case (lines, pos) if pos < (cs.size - 1) => lines map {insertBar(_, 2 * (level + 1))}
+				val cs = Vector(children(node): _*)
-				case (lines, pos) =>
+				val childLines = cs map {
-					if (lines.last.trim != "") lines ++ Vector(twoSpaces * (level + 1))
+					toAsciiLines(_, level + 1, parents + node)
-					else lines
+				}
+				val withBar = childLines.zipWithIndex flatMap {
+					case (lines, pos) if pos < (cs.size - 1) => lines map {
+						insertBar(_, 2 * (level + 1))
+					}
+					case (lines, pos) =>
+						if (lines.last.trim != "") lines ++ Vector(twoSpaces * (level + 1))
+						else lines
+				}
+				line +: withBar
 			}
-			line +: withBar
-		}
 
-		toAsciiLines(top, 0).mkString("\n")
+		toAsciiLines(top, 0, Set.empty).mkString("\n")
 	}
 
   def defaultColumnSize: Int = {

src/test/scala/net/virtualvoid/sbt/graph/util/AsciiTreeLayoutSpecs.scala

@@ -77,15 +77,18 @@ class AsciiTreeLayoutSpecs extends Specification {
             |  +-2
             |  | +-4
             |  | | +-3
-            |  | |
+            |  | |\u0020
             |  | +-5
             |  |   #-1
-            |  |   #-4
+            |  |   +-4
+            |  |   | +-3
+            |  |   |\u0020
             |  |   +-6
             |  |   +-7
-            |  |
+            |  |\u0020\u0020\u0020
-            |  #-3
+            |  +-3
-            |  #-4""".stripMargin.trim
+            |  +-4
+            |    +-3""".stripMargin.trim
     }
   }
 }