Create dynamic proxies in fewer dynamic assemblies

This corrects a bug that deviated from the original design. The idea was for all proxies to be generated into as few dynamic assemblies as possible. We have to allow for distinct dynamic assemblies for growing sets of skip visibility check attributes, but other than that we should reuse dynamic assemblies.
The bug here was that we were not supplying a structural `AssemblyName` equality comparer to our `ImmutableHashSet`. Since `AssemblyName.Equals` is a reference equality check and the CLR does not de-dupe assembly names, we must supply our own equality comparison in order to get the intended behavior.

Author: AArnott

src/StreamJsonRpc/AssemblyNameEqualityComparer.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+
+using System.Reflection;
+
+namespace StreamJsonRpc;
+
+internal class AssemblyNameEqualityComparer : IEqualityComparer<AssemblyName>
+{
+    internal static readonly IEqualityComparer<AssemblyName> Instance = new AssemblyNameEqualityComparer();
+
+    private AssemblyNameEqualityComparer()
+    {
+    }
+
+    public bool Equals(AssemblyName? x, AssemblyName? y)
+    {
+        if (x is null && y is null)
+        {
+            return true;
+        }
+
+        if (x is null || y is null)
+        {
+            return false;
+        }
+
+        return string.Equals(x.FullName, y.FullName, StringComparison.OrdinalIgnoreCase);
+    }
+
+    public int GetHashCode(AssemblyName obj)
+    {
+        Requires.NotNull(obj, nameof(obj));
+
+        return StringComparer.OrdinalIgnoreCase.GetHashCode(obj.FullName);
+    }
+}

src/StreamJsonRpc/ProxyGeneration.cs

@@ -752,7 +752,7 @@ private static ModuleBuilder GetProxyModuleBuilder(Type[] interfaceTypes)
         // For each set of skip visibility check assemblies, we need a dynamic assembly that skips at *least* that set.
         // The CLR will not honor any additions to that set once the first generated type is closed.
         // We maintain a dictionary to point at dynamic modules based on the set of skip visibility check assemblies they were generated with.
-        ImmutableHashSet<AssemblyName> skipVisibilityCheckAssemblies = ImmutableHashSet.CreateRange(interfaceTypes.SelectMany(t => SkipClrVisibilityChecks.GetSkipVisibilityChecksRequirements(t.GetTypeInfo())))
+        ImmutableHashSet<AssemblyName> skipVisibilityCheckAssemblies = ImmutableHashSet.CreateRange(AssemblyNameEqualityComparer.Instance, interfaceTypes.SelectMany(t => SkipClrVisibilityChecks.GetSkipVisibilityChecksRequirements(t.GetTypeInfo())))
             .Add(typeof(ProxyGeneration).Assembly.GetName());
         foreach ((ImmutableHashSet<AssemblyName> SkipVisibilitySet, ModuleBuilder Builder) existingSet in TransparentProxyModuleBuilderByVisibilityCheck)
         {

src/StreamJsonRpc/SkipClrVisibilityChecks.cs

@@ -79,7 +79,7 @@ internal static ImmutableHashSet<AssemblyName> GetSkipVisibilityChecksRequiremen
         Requires.NotNull(typeInfo, nameof(typeInfo));
 
         var visitedTypes = new HashSet<TypeInfo>();
-        ImmutableHashSet<AssemblyName>.Builder assembliesDeclaringInternalTypes = ImmutableHashSet.CreateBuilder<AssemblyName>(AssemblyNameEqualityComparer.Instance);
+        ImmutableHashSet<AssemblyName>.Builder assembliesDeclaringInternalTypes = ImmutableHashSet.CreateBuilder(AssemblyNameEqualityComparer.Instance);
         CheckForNonPublicTypes(typeInfo, assembliesDeclaringInternalTypes, visitedTypes);
 
         // Enumerate members on the interface that we're going to need to implement.
@@ -253,35 +253,4 @@ private TypeInfo EmitMagicAttribute()
 
         return tb.CreateTypeInfo()!;
     }
-
-    private class AssemblyNameEqualityComparer : IEqualityComparer<AssemblyName>
-    {
-        internal static readonly IEqualityComparer<AssemblyName> Instance = new AssemblyNameEqualityComparer();
-
-        private AssemblyNameEqualityComparer()
-        {
-        }
-
-        public bool Equals(AssemblyName? x, AssemblyName? y)
-        {
-            if (x is null && y is null)
-            {
-                return true;
-            }
-
-            if (x is null || y is null)
-            {
-                return false;
-            }
-
-            return string.Equals(x.FullName, y.FullName, StringComparison.OrdinalIgnoreCase);
-        }
-
-        public int GetHashCode(AssemblyName obj)
-        {
-            Requires.NotNull(obj, nameof(obj));
-
-            return StringComparer.OrdinalIgnoreCase.GetHashCode(obj.FullName);
-        }
-    }
 }

test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs

@@ -798,6 +798,18 @@ public async Task ValueTaskReturningMethod()
         await clientRpc.DoSomethingValueAsync();
     }
 
+    /// <summary>
+    /// Validates that similar proxies are generated in the same dynamic assembly.
+    /// </summary>
+    [Fact]
+    public void ReuseDynamicAssembliesTest()
+    {
+        JsonRpc clientRpc = new(Stream.Null);
+        IServer proxy1 = clientRpc.Attach<IServer>();
+        IServer2 proxy2 = clientRpc.Attach<IServer2>();
+        Assert.Same(proxy1.GetType().Assembly, proxy2.GetType().Assembly);
+    }
+
     public class EmptyClass
     {
     }