Fix #266 by stop recursively traversing a tree

core/shared/src/main/scala/coursier/util/Tree.scala

@@ -1,29 +1,56 @@
 package coursier.util
 
+import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
 
 object Tree {
 
   def apply[T](roots: IndexedSeq[T])(children: T => Seq[T], print: T => String): String = {
+    /**
+      * Add elements to the stack
+      * @param stack a mutable stack which will have elements
+      * @param elems elements to add
+      * @param isLast a list that contains whether an element is the last in its siblings or not.
+      *               The first element is the deepest, due to the fact prepending a List is faster than appending
+      */
+    def push(stack: mutable.Stack[(T, List[Boolean])], elems: Seq[T], isLast: List[Boolean]) = {
+      // Reverse the list because the stack is LIFO but elems must be shown in the order
+      for ((x, idx) <- elems.zipWithIndex.reverse) {
+        stack.push((x, (idx == elems.length - 1) :: isLast))
+      }
+    }
 
-    def helper(elems: Seq[T], prefix: String, acc: String => Unit): Unit =
-      for ((elem, idx) <- elems.zipWithIndex) {
-        val isLast = idx == elems.length - 1
+    def prefix(isLast: List[Boolean]): String = {
+      // Reverse the list because its first element is the deepest element
+      isLast.reverse.zipWithIndex.map {
+        case (last, idx) =>
+          if (idx == isLast.length - 1)
+            if (last) "└─ " else "├─ "
+          else
+            if (last) "   " else "|  "
+      }.mkString("")
+    }
 
-        val tee = if (isLast) "└─ " else "├─ "
+    // Depth-first traverse
+    def helper(elems: Seq[T], acc: String => Unit): Unit = {
+      val stack = new mutable.Stack[(T, List[Boolean])]()
+      val seen = new mutable.HashSet[T]()
 
-        acc(prefix + tee + print(elem))
+      push(stack, elems, List[Boolean]())
 
-        val children0 = children(elem)
+      while (stack.nonEmpty) {
+        val (elem, isLast) = stack.pop()
+        acc(prefix(isLast) + print(elem))
 
-        if (children0.nonEmpty) {
-          val extraPrefix = if (isLast) "   " else "|  "
-          helper(children0, prefix + extraPrefix, acc)
+        if (! seen.contains(elem)) {
+          push(stack, children(elem), isLast)
+          seen.add(elem)
         }
       }
+    }
 
     val b = new ArrayBuffer[String]
-    helper(roots, "", b += _)
+    helper(roots, b += _)
     b.mkString("\n")
   }
 

tests/shared/src/test/scala/coursier/test/TreeTests.scala

@@ -0,0 +1,35 @@
+package coursier
+package test
+
+import coursier.util.{Tree, Xml}
+import utest._
+
+object TreeTests extends TestSuite {
+  private def tree(str: String, xs: Array[Xml.Node] = Array()): Xml.Node = {
+    new Xml.Node {
+      override def label: String = str
+      override def children = xs
+
+      override def attributes: Seq[(String, String, String)] = Array[(String, String, String)]()
+      override def isText: Boolean = false
+      override def textContent: String = ""
+      override def isElement: Boolean = true
+    }
+  }
+
+  val roots = Array(
+    tree("p1", Array(tree("c1"), tree("c2"))),
+    tree("p2", Array(tree("c3"), tree("c4"))))
+
+  val tests = TestSuite {
+    'apply {
+      val str = Tree(roots)(_.children, _.label)
+      assert(str == """├─ p1
+        ||  ├─ c1
+        ||  └─ c2
+        |└─ p2
+        |   ├─ c3
+        |   └─ c4""".stripMargin)
+    }
+  }
+}