Rule chaining in RulesEngine suffered from exponential performance degradation as reported in #471

src/RulesEngine/Actions/EvaluateRuleAction.cs

@@ -28,8 +28,28 @@ internal async override ValueTask<ActionRuleResult> ExecuteAndReturnResultAsync(
             List<RuleResultTree> resultList = null;
             if (includeRuleResults)
             {
-                resultList = new List<RuleResultTree>(output?.Results ?? new List<RuleResultTree>() { });
-                resultList.AddRange(innerResult.Results);
+                // Avoid exponential copying by only including the immediate results from this execution
+                // The chained rule results are already included in output?.Results
+                resultList = new List<RuleResultTree>();
+
+                // Add the chained rule results (from the EvaluateRule action execution)
+                if (output?.Results != null)
+                {
+                    resultList.AddRange(output.Results);
+                }
+
+                // Add the parent rule that triggered this chain (but avoid duplicating it)
+                if (innerResult.Results != null)
+                {
+                    foreach (var result in innerResult.Results)
+                    {
+                        // Only add if it's not already in the output results to avoid duplication
+                        if (output?.Results == null || !output.Results.Any(r => ReferenceEquals(r, result)))
+                        {
+                            resultList.Add(result);
+                        }
+                    }
+                }
             }
             return new ActionRuleResult {
                 Output = output?.Output,

src/RulesEngine/RulesEngine.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
 using FluentValidation;
@@ -128,11 +128,33 @@ private async ValueTask ExecuteActionAsync(IEnumerable<RuleResultTree> ruleResul
 
         public async ValueTask<ActionRuleResult> ExecuteActionWorkflowAsync(string workflowName, string ruleName, RuleParameter[] ruleParameters)
         {
-            var compiledRule = CompileRule(workflowName, ruleName, ruleParameters);
+            var compiledRule = GetCompiledRule(workflowName, ruleName, ruleParameters);
             var resultTree = compiledRule(ruleParameters);
             return await ExecuteActionForRuleResult(resultTree, true);
         }
 
+        private RuleFunc<RuleResultTree> GetCompiledRule(string workflowName, string ruleName, RuleParameter[] ruleParameters)
+        {
+            // Ensure the workflow is registered and rules are compiled
+            if (!RegisterRule(workflowName, ruleParameters))
+            {
+                throw new ArgumentException($"Rule config file is not present for the {workflowName} workflow");
+            }
+
+            // Get the compiled rule from cache
+            var compiledRulesCacheKey = GetCompiledRulesKey(workflowName, ruleParameters);
+            var compiledRules = _rulesCache.GetCompiledRules(compiledRulesCacheKey);
+
+            if (compiledRules?.TryGetValue(ruleName, out var compiledRule) == true)
+            {
+                return compiledRule;
+            }
+
+            // Fallback to individual compilation if not found in cache
+            // This should rarely happen, but provides safety
+            return CompileRule(workflowName, ruleName, ruleParameters);
+        }
+
         private async ValueTask<ActionRuleResult> ExecuteActionForRuleResult(RuleResultTree resultTree, bool includeRuleResults = false)
         {
             var ruleActions = resultTree?.Rule?.Actions;