Defense against circular references in Promotions (#9694)

* Promotion picker - working defense against circular references

* Mod checker - complain about circular references

core/src/com/unciv/models/ruleset/RulesetValidator.kt

@@ -10,6 +10,7 @@ import com.unciv.models.ruleset.unique.IHasUniques
 import com.unciv.models.ruleset.unique.StateForConditionals
 import com.unciv.models.ruleset.unique.Unique
 import com.unciv.models.ruleset.unique.UniqueType
+import com.unciv.models.ruleset.unit.Promotion
 import com.unciv.models.stats.INamed
 import com.unciv.models.stats.Stats
 
@@ -387,6 +388,7 @@ class RulesetValidator(val ruleset: Ruleset) {
                 if (!ruleset.unitTypes.containsKey(unitType) && (ruleset.unitTypes.isNotEmpty() || !vanillaRuleset.unitTypes.containsKey(unitType)))
                     lines.add("${promotion.name} references unit type $unitType, which does not exist!", RulesetErrorSeverity.Warning)
             checkUniques(promotion, lines, rulesetSpecific, tryFixUnknownUniques)
+            checkPromotionCircularReferences(lines)
         }
 
         for (unitType in ruleset.unitTypes.values) {
@@ -426,6 +428,24 @@ class RulesetValidator(val ruleset: Ruleset) {
         return lines
     }
 
+    private fun checkPromotionCircularReferences(lines: RulesetErrorList) {
+        fun recursiveCheck(history: LinkedHashSet<Promotion>, promotion: Promotion, level: Int) {
+            if (promotion in history) {
+                lines.add("Circular Reference in Promotions: ${history.joinToString("→") { it.name }}→${promotion.name}", RulesetErrorSeverity.Warning)
+                return
+            }
+            if (level > 99) return
+            history.add(promotion)
+            for (prerequisiteName in promotion.prerequisites) {
+                val prerequisite = ruleset.unitPromotions[prerequisiteName] ?: continue
+                recursiveCheck(history.toCollection(linkedSetOf()), prerequisite, level + 1)
+            }
+        }
+        for (promotion in ruleset.unitPromotions.values) {
+            recursiveCheck(linkedSetOf(), promotion, 0)
+        }
+    }
+
 
     fun checkUniques(
         uniqueContainer: IHasUniques,

core/src/com/unciv/ui/screens/pickerscreens/PromotionTree.kt

@@ -6,7 +6,6 @@ import com.unciv.models.ruleset.unique.StateForConditionals
 import com.unciv.models.ruleset.unique.UniqueType
 import com.unciv.models.ruleset.unit.Promotion
 import com.unciv.models.translations.tr
-import com.unciv.utils.Log
 
 internal class PromotionTree(val unit: MapUnit) {
     /** Ordered set of Promotions to show - by Json column/row and translated name */
@@ -92,10 +91,7 @@ internal class PromotionTree(val unit: MapUnit) {
         for (node in nodes.values) {
             for (prerequisite in node.promotion.prerequisites) {
                 val parent = nodes[prerequisite] ?: continue
-                if (node in allChildren(parent)) {
+                if (detectLoop(node, parent)) continue
-                    Log.debug("Ignoring circular reference: %s requires %s", node, parent)
-                    continue
-                }
                 node.parents += parent
                 parent.children += node
                 if (node.level > 0 && node.baseName == parent.baseName)
@@ -153,8 +149,21 @@ internal class PromotionTree(val unit: MapUnit) {
 
     fun allNodes() = nodes.values.asSequence()
     fun allRoots() = allNodes().filter { it.isRoot }
-    private fun allChildren(node: PromotionNode): Sequence<PromotionNode> {
+
-        return sequenceOf(node) + node.children.flatMap { allChildren(it) }
+    private fun detectLoop(node: PromotionNode, parent: PromotionNode): Boolean {
+        if (parent == node) return true
+        val loopCheck = HashSet<PromotionNode>(nodes.size)
+        loopCheck.add(node)
+        fun detectRecursive(parent: PromotionNode, level: Int): Boolean {
+            if (level > 99) return true
+            if (parent in loopCheck) return true
+            loopCheck.add(parent)
+            for (child in parent.children) {
+                if (detectRecursive(child, level + 1)) return true
+            }
+            return false
+        }
+        return detectRecursive(parent, 0)
     }
 
     private fun getReachableNode(promotion: Promotion): PromotionNode? =