Add optional hash collision mitigation to ServiceRegistry

src/Lamar/IoC/LamarInstanceHashCollisionException.cs

@@ -0,0 +1,14 @@
+using System.Collections.Generic;
+using System;
+using System.Linq;
+using JasperFx.Core.Reflection;
+
+namespace Lamar.IoC;
+
+public class LamarInstanceHashCollisionException : LamarException
+{
+    public LamarInstanceHashCollisionException(int instanceHash, IEnumerable<Type> serviceTypes) : base(
+        $"Duplicate hash '{instanceHash}' generated for services: {string.Join(", ", serviceTypes.Select(x => x.FullNameInCode()))}")
+    {
+    }
+}

src/Lamar/ServiceRegistry.HashCollisionMitigation.cs

@@ -0,0 +1,75 @@
+using Lamar.IoC;
+using Lamar.IoC.Instances;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Lamar;
+
+public partial class ServiceRegistry
+{
+    /// <summary>
+    /// Finds and mitigates <see cref="Instance"/> hash code collisions in the current <see cref="ServiceRegistry"/> instance.<br/>
+	/// Hash codes are regenerated by renaming the instances where collisions exist with the provided <paramref name="instanceRenamePolicy"/>.<br/>
+	/// When the <paramref name="retryLimit"/> is met, and a hash collision is detected, a <see cref="LamarInstanceHashCollisionException" /> is thrown.
+    /// </summary>
+    /// <param name="retryLimit"></param>
+    /// <param name="instanceRenamePolicy"></param>
+    /// <exception cref="LamarInstanceHashCollisionException"></exception>
+    public void MitigateInstanceHashCollisions(int retryLimit = 3, Func<string, string> instanceRenamePolicy = null)
+    {
+        bool shouldMitigateCollisions = true;
+        int remaininingRetries = retryLimit;
+
+        Func<string, string> renameInstance = instanceRenamePolicy ?? (name => $"{name}_x");
+
+        while (shouldMitigateCollisions && remaininingRetries > 0)
+        {
+            shouldMitigateCollisions = TryRemoveInstanceHashCollisions(renameInstance);
+            remaininingRetries--;
+        }
+
+        var collision = GetInstanceHashCollisions().FirstOrDefault();
+
+        if (collision != null)
+        {
+            throw new LamarInstanceHashCollisionException(collision.Key, collision.Select(x => x.ServiceType));
+        }
+    }
+
+    internal bool TryRemoveInstanceHashCollisions(Func<string, string> instanceRenamePolicy)
+    {
+        var hasCollision = false;
+
+        foreach (var collision in GetInstanceHashCollisions())
+        {
+            hasCollision = true;
+            HandleInstanceHashCollisions(collision, instanceRenamePolicy);
+        }
+
+        return hasCollision;
+    }
+
+    internal void HandleInstanceHashCollisions(IGrouping<int, Instance> collision, Func<string, string> instanceRenamePolicy)
+    {
+        var namedInstances = collision.Where(x => x.IsExplicitlyNamed).ToList();
+
+        if (namedInstances.Count > 1)
+        {
+            throw new LamarInstanceHashCollisionException(collision.Key, namedInstances.Select(x => x.ServiceType));
+        }
+
+        foreach (var instance in collision.Except(namedInstances))
+        {
+            instance.Name = instanceRenamePolicy(instance.Name);
+        }
+    }
+
+    internal IEnumerable<IGrouping<int, Instance>> GetInstanceHashCollisions()
+    {
+        return this.Select(x => x.ImplementationInstance)
+            .OfType<Instance>()
+            .GroupBy(x => x.Hash)
+            .Where(x => x.Select(y => y.ServiceType).Distinct().Count() > 1);
+    }
+}