elsa-workflows/elsa-core · error · Exception

Cyclic dependency found

Error message

Cyclic dependency found

What it means

EnumerableTopologicalSortExtensions performs a depth-first topological sort of dependency-ordered items (used by Elsa features). When a cycle is detected and throwOnCycle is enabled, it throws a generic Exception('Cyclic dependency found').

Solutions

1. Break the cycle by removing the back-dependency from one feature's Dependencies list
2. Move shared logic into a lower-level feature that both depend on
3. Review the feature dependency graph and ensure it forms a DAG

Example fix

// before
class FeatureA : FeatureBase { public override IEnumerable<Type> Dependencies => new[] { typeof(FeatureB) }; }
class FeatureB : FeatureBase { public override IEnumerable<Type> Dependencies => new[] { typeof(FeatureA) }; }
// after
class FeatureB : FeatureBase { public override IEnumerable<Type> Dependencies => Array.Empty<Type>(); }

// detect cycle before registering
var deps = new Dictionary<Type, IEnumerable<Type>> { [typeof(FeatureA)] = typeof(FeatureA).GetDependencies() /* etc */ };
// run sort with throwOnCycle: false and inspect remaining unsorted items

try { features.TSort(f => f.Dependencies, f => f.DependsOn, throwOnCycle: true); } catch (Exception e) when (e.Message == "Cyclic dependency found") { logger.LogError("Feature dependency cycle detected"); }

When it happens

Trigger: Registering features (or any items with Dependencies) such that A depends on B and B (directly or transitively) depends on A, then running the topological sort.

Common situations: Custom Elsa feature declaring a dependency on a feature that (transitively) depends back on it; copying dependency lists between features creating a loop; plugin conflicts after package upgrades.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

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AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/26441da0543be027. Report an issue: GitHub.

Appendix: source

Thrown at src/common/Elsa.Features/Extensions/EnumerableTopologicalSortExtensions.cs:36

        foreach (var item in source)
            Visit(item, visited, sorted, dependencies, throwOnCycle);

        return sorted;
    }

    private static void Visit<T>(T item, ISet<T> visited, ICollection<T> sorted, Func<T, IEnumerable<T>> dependencies, bool throwOnCycle)
    {
        if (visited.Add(item))
        {
            foreach (var dep in dependencies(item))
                Visit(dep, visited, sorted, dependencies, throwOnCycle);

            sorted.Add(item);
        }
        else
        {
            if (throwOnCycle && !sorted.Contains(item))
                throw new Exception("Cyclic dependency found");
        }
    }
}

View on GitHub (pinned to fe9217bdfa)