feat(model-api): Introduce property to specify whether a child link is ordered

Author: Oleksandr Dzhychko

model-api/src/commonMain/kotlin/org/modelix/model/api/IChildLink.kt

@@ -30,6 +30,16 @@ interface IChildLink : ILink {
     companion object {
         fun fromName(name: String): IChildLink = ChildLinkFromName(name)
     }
+
+    /**
+     * Whether children with this role are returned in a meaningful order and whether they are allowed to be reordered.
+     *
+     * Children returned for an unordered role might be returned in a different order in subsequent request.
+     * If a child role is not ordered, implementations of [[INode.moveChild]] are allowed to fail
+     * when instructed to move a node in between existing nodes.
+     */
+    val isOrdered
+        get() = true
 }
 
 data class ChildLinkFromName(override val name: String) : LinkFromName(), IChildLink {

model-api/src/commonMain/kotlin/org/modelix/model/api/INode.kt

@@ -380,6 +380,21 @@ fun INode.tryResolveProperty(role: String): IProperty? {
         ?: allLinks.find { it.getSimpleName() == role }
         ?: allLinks.find { it.getUID() == role }
 }
+
+/**
+ * Resolves whether the child link is ordered or not.
+ *
+ * Assume children to be ordered by default.
+ * Unordered children are the special case that can be declared by setting [[IChildLink.isOrdered]] to `false`.
+ */
+fun INode.isChildRoleOrdered(role: String?): Boolean {
+    return if (role == null) {
+        true
+    } else {
+        this.tryResolveChildLink(role)?.isOrdered ?: true
+    }
+}
+
 fun INode.resolvePropertyOrFallback(role: String): IProperty {
     return tryResolveProperty(role) ?: IProperty.fromName(role)
 }

model-api/src/commonMain/kotlin/org/modelix/model/api/SimpleChildLink.kt

@@ -19,6 +19,7 @@ class SimpleChildLink(
     override val isOptional: Boolean,
     override val targetConcept: IConcept,
     private val uid: String? = null,
+    override val isOrdered: Boolean = true,
 ) : IChildLink {
     var owner: SimpleConcept? = null
     override val childConcept: IConcept = targetConcept