model: Eliminate the use of a SortedSet

model/src/main/kotlin/DependencyGraph.kt

@@ -26,6 +26,7 @@ import com.fasterxml.jackson.databind.annotation.JsonSerialize
 import java.util.SortedSet
 
 import org.ossreviewtoolkit.model.utils.DependencyGraphEdgeSortedSetConverter
+import org.ossreviewtoolkit.model.utils.DependencyReferenceSortedSetConverter
 import org.ossreviewtoolkit.model.utils.PackageLinkageValueFilter
 
 /**
@@ -317,7 +318,8 @@ class DependencyReference(
     /**
      * A set with the references to the dependencies of this dependency. That way a tree-like structure is established.
      */
-    val dependencies: SortedSet<DependencyReference> = sortedSetOf(),
+    @JsonSerialize(contentConverter = DependencyReferenceSortedSetConverter::class)
+    val dependencies: Set<DependencyReference> = emptySet(),
 
     /**
      * The type of linkage used for the referred package from its dependent package. As most of our supported
@@ -400,10 +402,10 @@ private fun DependencyReference.toGraphNode() = DependencyGraphNode(pkg, fragmen
 /**
  * Construct a mapping of dependencies based on the given [roots].
  */
-private fun constructNodeDependenciesFromScopeRoots(roots: SortedSet<DependencyReference>): NodeDependencies {
+private fun constructNodeDependenciesFromScopeRoots(roots: Set<DependencyReference>): NodeDependencies {
     val mapping = mutableMapOf<DependencyGraphNode, List<DependencyGraphNode>>()
 
-    fun construct(refs: SortedSet<DependencyReference>) {
+    fun construct(refs: Set<DependencyReference>) {
         refs.forEach { ref ->
             val node = ref.toGraphNode()
             if (node !in mapping) {

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

@@ -370,7 +370,7 @@ class DependencyGraphBuilder<D>(
         transitive: Boolean,
         processed: Set<D>
     ): DependencyReference? {
-        val transitiveDependencies = dependencyHandler.dependenciesFor(dependency).mapNotNull {
+        val transitiveDependencies = dependencyHandler.dependenciesFor(dependency).mapNotNullTo(mutableSetOf()) {
             addDependencyToGraph(scopeName, it, transitive = true, processed)
         }
 
@@ -387,7 +387,7 @@ class DependencyGraphBuilder<D>(
         val ref = DependencyReference(
             pkg = index.root,
             fragment = index.fragment,
-            dependencies = transitiveDependencies.toSortedSet(),
+            dependencies = transitiveDependencies,
             linkage = dependencyHandler.linkageFor(dependency),
             issues = issues
         )

model/src/main/kotlin/utils/SortedSetConverters.kt → model/src/main/kotlin/utils/SortedCollectionConverters.kt

@@ -28,6 +28,7 @@ import java.util.SortedSet
 import org.ossreviewtoolkit.model.ArtifactProvenance
 import org.ossreviewtoolkit.model.CopyrightFinding
 import org.ossreviewtoolkit.model.DependencyGraphEdge
+import org.ossreviewtoolkit.model.DependencyReference
 import org.ossreviewtoolkit.model.FileList
 import org.ossreviewtoolkit.model.Identifier
 import org.ossreviewtoolkit.model.LicenseFinding
@@ -49,6 +50,11 @@ class DependencyGraphEdgeSortedSetConverter : StdConverter<Set<DependencyGraphEd
     override fun convert(value: Set<DependencyGraphEdge>) = value.toSortedSet(compareBy({ it.from }, { it.to }))
 }
 
+class DependencyReferenceSortedSetConverter : StdConverter<Set<DependencyReference>, SortedSet<DependencyReference>>() {
+    override fun convert(value: Set<DependencyReference>) =
+        value.toSortedSet(compareBy({ it.pkg.toString() }, { it.fragment }))
+}
+
 /** Do not convert to SortedSet in order to not require a comparator consistent with equals */
 class FileListSortedSetConverter : StdConverter<Set<FileList>, Set<FileList>>() {
     override fun convert(value: Set<FileList>) = value.sortedBy { it.provenance.getSortKey() }.toSet()

model/src/test/kotlin/DependencyGraphTest.kt

@@ -93,8 +93,8 @@ class DependencyGraphTest : WordSpec({
             )
             val refLang = DependencyReference(0)
             val refCollections = DependencyReference(1)
-            val refConfig = DependencyReference(2, dependencies = sortedSetOf(refLang, refCollections))
-            val refCsv = DependencyReference(3, dependencies = sortedSetOf(refConfig))
+            val refConfig = DependencyReference(2, dependencies = setOf(refLang, refCollections))
+            val refCsv = DependencyReference(3, dependencies = setOf(refConfig))
             val fragments = sortedSetOf(DependencyGraph.DEPENDENCY_REFERENCE_COMPARATOR, refCsv)
             val scopeMap = mapOf("s" to listOf(RootDependencyIndex(3)))
             val graph = DependencyGraph(ids, fragments, scopeMap)
@@ -113,10 +113,10 @@ class DependencyGraphTest : WordSpec({
             val refLogging = DependencyReference(3)
             val refLang = DependencyReference(0)
             val refCollections1 = DependencyReference(1)
-            val refCollections2 = DependencyReference(1, fragment = 1, dependencies = sortedSetOf(refLogging))
-            val refConfig1 = DependencyReference(2, dependencies = sortedSetOf(refLang, refCollections1))
+            val refCollections2 = DependencyReference(1, fragment = 1, dependencies = setOf(refLogging))
+            val refConfig1 = DependencyReference(2, dependencies = setOf(refLang, refCollections1))
             val refConfig2 =
-                DependencyReference(2, fragment = 1, dependencies = sortedSetOf(refLang, refCollections2))
+                DependencyReference(2, fragment = 1, dependencies = setOf(refLang, refCollections2))
             val fragments = sortedSetOf(refConfig1, refConfig2)
             val scopeMap = mapOf(
                 "s1" to listOf(RootDependencyIndex(2)),
@@ -170,7 +170,7 @@ class DependencyGraphTest : WordSpec({
             )
             val issue = Issue(source = "analyzer", message = "Could not analyze :-(")
             val refLang = DependencyReference(0, linkage = PackageLinkage.PROJECT_DYNAMIC)
-            val refCol = DependencyReference(1, issues = listOf(issue), dependencies = sortedSetOf(refLang))
+            val refCol = DependencyReference(1, issues = listOf(issue), dependencies = setOf(refLang))
             val trees = sortedSetOf(refCol)
             val scopeMap = mapOf("s" to listOf(RootDependencyIndex(1)))
 

model/src/test/kotlin/ProjectTest.kt

@@ -59,10 +59,10 @@ private fun createDependencyGraph(qualified: Boolean = false): DependencyGraph {
         exampleId
     )
     val langRef = DependencyReference(0)
-    val textRef = DependencyReference(1, dependencies = sortedSetOf(langRef))
+    val textRef = DependencyReference(1, dependencies = setOf(langRef))
     val strutsRef = DependencyReference(2)
-    val csvRef = DependencyReference(3, dependencies = sortedSetOf(langRef))
-    val exampleRef = DependencyReference(4, dependencies = sortedSetOf(textRef, strutsRef))
+    val csvRef = DependencyReference(3, dependencies = setOf(langRef))
+    val exampleRef = DependencyReference(4, dependencies = setOf(textRef, strutsRef))
 
     val plainScopeMapping = mapOf(
         "default" to listOf(RootDependencyIndex(4)),