From 9f28128db52615c7c631e7cdb5937eae6a4cf28a Mon Sep 17 00:00:00 2001
From: Matthew Edmondson <matthew.edmondson@gmail.com>
Date: Fri, 9 Oct 2026 04:26:53 +0000
Subject: [PATCH] fix: register each generator once when AddCoder is called
 twice [patch]

AddLanguageGenerators appended a descriptor per call, so calling AddCoder
from both a library and its host resolved fourteen generators and the
documented .Single(g => g.LanguageId == ...) lookup threw. Register the
generators with TryAddEnumerable and the serializers with TryAddSingleton,
and make the idempotency test assert one registration of each.

Fixes #150

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ACXyQBPWSqFJuF51Mx6FNh
---
 .../ServiceCollectionExtensionsTests.cs       | 10 ++++++++-
 Coder/ServiceCollectionExtensions.cs          | 22 ++++++++++---------
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/Coder.Test/ServiceCollectionExtensionsTests.cs b/Coder.Test/ServiceCollectionExtensionsTests.cs
index 0f90ce0..5707c51 100644
--- a/Coder.Test/ServiceCollectionExtensionsTests.cs
+++ b/Coder.Test/ServiceCollectionExtensionsTests.cs
@@ -200,7 +200,15 @@ public void AddCoder_ShouldBeIdempotent()
 		YamlSerializer? serializer = serviceProvider.GetService<YamlSerializer>();
 		YamlDeserializer? deserializer = serviceProvider.GetService<YamlDeserializer>();
 
-		Assert.IsTrue(generators.Count > 0, "Generators should still be registered");
+		Assert.HasCount(7, generators, "Each generator should be registered once however often AddCoder is called");
+		foreach (string languageId in new[] { "python", "csharp", "javascript", "cpp", "c", "rust", "go" })
+		{
+			ILanguageGenerator generator = generators.Single(g => g.LanguageId == languageId);
+			Assert.IsNotNull(generator, $"{languageId} should resolve to exactly one generator");
+		}
+
+		Assert.HasCount(1, serviceProvider.GetServices<YamlSerializer>(), "Serializer should be registered once");
+		Assert.HasCount(1, serviceProvider.GetServices<YamlDeserializer>(), "Deserializer should be registered once");
 		Assert.IsNotNull(serializer, "Serializer should still be registered");
 		Assert.IsNotNull(deserializer, "Deserializer should still be registered");
 	}
diff --git a/Coder/ServiceCollectionExtensions.cs b/Coder/ServiceCollectionExtensions.cs
index ead643d..843ec0f 100644
--- a/Coder/ServiceCollectionExtensions.cs
+++ b/Coder/ServiceCollectionExtensions.cs
@@ -4,6 +4,7 @@ namespace ktsu.Coder;
 
 using ktsu.Coder.Languages;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 
 /// <summary>
 /// Extension methods for configuring Coder services in dependency injection containers.
@@ -19,14 +20,15 @@ public static IServiceCollection AddLanguageGenerators(this IServiceCollection s
 	{
 		Ensure.NotNull(services);
 
-		// Register all available language generators
-		services.AddSingleton<ILanguageGenerator, PythonGenerator>();
-		services.AddSingleton<ILanguageGenerator, CSharpGenerator>();
-		services.AddSingleton<ILanguageGenerator, JavaScriptGenerator>();
-		services.AddSingleton<ILanguageGenerator, CppGenerator>();
-		services.AddSingleton<ILanguageGenerator, CGenerator>();
-		services.AddSingleton<ILanguageGenerator, RustGenerator>();
-		services.AddSingleton<ILanguageGenerator, GoGenerator>();
+		// Register all available language generators. TryAddEnumerable skips a generator that is
+		// already registered, so calling this twice still resolves one of each.
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, PythonGenerator>());
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, CSharpGenerator>());
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, JavaScriptGenerator>());
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, CppGenerator>());
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, CGenerator>());
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, RustGenerator>());
+		services.TryAddEnumerable(ServiceDescriptor.Singleton<ILanguageGenerator, GoGenerator>());
 
 		return services;
 	}
@@ -40,8 +42,8 @@ public static IServiceCollection AddCoderSerialization(this IServiceCollection s
 	{
 		Ensure.NotNull(services);
 
-		services.AddSingleton<Serialization.YamlSerializer>();
-		services.AddSingleton<Serialization.YamlDeserializer>();
+		services.TryAddSingleton<Serialization.YamlSerializer>();
+		services.TryAddSingleton<Serialization.YamlDeserializer>();
 
 		return services;
 	}