refactor(model): Use sets instead of lists for DependencyGraphEdge

It is not necessary to allow for having multiple edges between any pair
of nodes. So, always operate with sets to reflect that.

Note that order of edges is not important either (even if a set usually
maintains insertion order).

Signed-off-by: Frank Viernau <frank_viernau@epam.com>

model/src/main/kotlin/DependencyGraph.kt

@@ -99,10 +99,10 @@ data class DependencyGraph(
     val nodes: List<DependencyGraphNode>? = null,
 
     /**
-     * A list with the edges of this dependency graph. By traversing the edges, the dependencies of packages can be
+     * A set with the edges of this dependency graph. By traversing the edges, the dependencies of packages can be
      * determined.
      */
-    val edges: List<DependencyGraphEdge>? = null
+    val edges: Set<DependencyGraphEdge>? = null
 ) {
     companion object {
         /**
@@ -419,7 +419,7 @@ private fun constructNodeDependenciesFromScopeRoots(roots: SortedSet<DependencyR
  */
 private fun constructNodeDependenciesFromGraph(
     nodes: List<DependencyGraphNode>,
-    edges: List<DependencyGraphEdge>
+    edges: Set<DependencyGraphEdge>
 ): NodeDependencies {
     val mapping = mutableMapOf<DependencyGraphNode, MutableList<DependencyGraphNode>>()
 

model/src/main/kotlin/utils/DependencyGraphBuilder.kt

@@ -179,7 +179,7 @@ class DependencyGraphBuilder<D>(
         )
     }
 
-    private fun Collection<DependencyGraphEdge>.removeCycles(): List<DependencyGraphEdge> {
+    private fun Set<DependencyGraphEdge>.removeCycles(): Set<DependencyGraphEdge> {
         val edges = toMutableSet()
         val edgesToKeep = breakCycles(edges)
         val edgesToRemove = edges - edgesToKeep
@@ -188,7 +188,7 @@ class DependencyGraphBuilder<D>(
             logger.warn { "Removing edge '${it.from} -> ${it.to}' to break a cycle." }
         }
 
-        return filter { it in edgesToKeep }
+        return filterTo(mutableSetOf()) { it in edgesToKeep }
     }
 
     private fun checkReferences() {
@@ -436,9 +436,9 @@ class DependencyGraphBuilder<D>(
  */
 private fun Collection<DependencyReference>.toGraph(
     indexMapping: IntArray
-): Pair<List<DependencyGraphNode>, List<DependencyGraphEdge>> {
+): Pair<List<DependencyGraphNode>, Set<DependencyGraphEdge>> {
     val nodes = mutableSetOf<DependencyGraphNode>()
-    val edges = mutableListOf<DependencyGraphEdge>()
+    val edges = mutableSetOf<DependencyGraphEdge>()
     val nodeIndices = mutableMapOf<NodeKey, Int>()
 
     fun getOrAddNodeIndex(ref: DependencyReference): Int =

model/src/test/kotlin/DependencyGraphTest.kt

@@ -144,7 +144,7 @@ class DependencyGraphTest : WordSpec({
             val nodeConfig1 = DependencyGraphNode(2)
             val nodeConfig2 = DependencyGraphNode(2, fragment = 1)
             val nodes = listOf(nodeLogging, nodeLang, nodeCollections1, nodeCollections2, nodeConfig1, nodeConfig2)
-            val edges = listOf(
+            val edges = setOf(
                 DependencyGraphEdge(3, 0),
                 DependencyGraphEdge(4, 1),
                 DependencyGraphEdge(4, 2),