Consider nullability in ReferenceIndexerBase (#45714)

src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

@@ -128055,5 +128055,26 @@ public new void M1<T>(System.Nullable<T?> x)
                 Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, "x").WithArguments("System.Nullable<T>", "T", "T").WithLocation(11, 47)
                 );
         }
+
+        [Fact]
+        [WorkItem(44348, "https://github.com/dotnet/roslyn/issues/44348")]
+        public void Constraints()
+        {
+            var source =
+@"class A<T, U>
+{
+    internal interface IA { }
+    internal class C { }
+}
+#nullable enable
+class B<T, U> : A<T, U>
+    where T : B<T, U>.IB
+    where U : A<T, U>.C
+{
+    internal interface IB : IA { }
+}";
+            var comp = CreateCompilation(source);
+            comp.VerifyEmitDiagnostics();
+        }
     }
 }

src/Compilers/Core/Portable/PEWriter/ReferenceIndexerBase.cs

@@ -5,7 +5,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using Roslyn.Utilities;
 using EmitContext = Microsoft.CodeAnalysis.Emit.EmitContext;
 using Microsoft.CodeAnalysis.Emit;
 
@@ -13,8 +12,8 @@ namespace Microsoft.Cci
 {
     internal abstract class ReferenceIndexerBase : MetadataVisitor
     {
-        private readonly HashSet<IReference> _alreadySeen = new HashSet<IReference>();
-        private readonly HashSet<IReference> _alreadyHasToken = new HashSet<IReference>();
+        private readonly HashSet<IReference> _alreadySeen = new HashSet<IReference>(MetadataEntityReferenceComparer.ConsiderEverything);
+        private readonly HashSet<IReference> _alreadyHasToken = new HashSet<IReference>(MetadataEntityReferenceComparer.ConsiderEverything);
         protected bool typeReferenceNeedsToken;
 
         internal ReferenceIndexerBase(EmitContext context)