Fix nested in generic type binding issues in enabled nullability context

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

@@ -6046,7 +6046,7 @@ private BoundExpression BindLeftIdentifierOfPotentialColorColorMemberAccess(Iden
                         {
                             var typeDiagnostics = BindingDiagnosticBag.Create(diagnostics);
                             var boundType = BindNamespaceOrType(left, typeDiagnostics);
-                            if (TypeSymbol.Equals(boundType.Type, leftType, TypeCompareKind.ConsiderEverything2))
+                            if (TypeSymbol.Equals(boundType.Type, leftType, TypeCompareKind.AllIgnoreOptions))
                             {
                                 // NOTE: ReplaceTypeOrValueReceiver will call CheckValue explicitly.
                                 boundValue = BindToNaturalType(boundValue, valueDiagnostics);

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

@@ -2182,5 +2182,151 @@ class C2
                 Diagnostic(ErrorCode.ERR_MethDelegateMismatch, "new System.Action(C2.ReferenceEquals)").WithArguments("ReferenceEquals", "System.Action").WithLocation(9, 13)
                 );
         }
+
+        [WorkItem(61171, "https://github.com/dotnet/roslyn/issues/61171")]
+        [Theory]
+        [InlineData(null)]
+        [InlineData("class")]
+        [InlineData("struct")]
+        [InlineData("unmanaged")]
+        [InlineData("notnull")]
+        public void WorkItem61171_Constraints(string constraint)
+        {
+            string constraintLine = $"where TValue : {constraint}";
+            if (string.IsNullOrEmpty(constraint))
+            {
+                constraintLine = "";
+            }
+
+            string source = $@"
+#nullable enable
+
+namespace DataStructures.Trees;
+
+public sealed class Tree<TValue>
+    {constraintLine}
+{{
+    public abstract class Node
+    {{
+        public abstract NodeType NodeType {{ get; }}
+    }}
+
+    public sealed class ParentNode : Node
+    {{
+        public override NodeType NodeType => Tree<TValue>.NodeType.Parent;
+    }}
+
+    public sealed class LeafNode : Node
+    {{
+        public override Tree<TValue>.NodeType NodeType => NodeType.Leaf;
+    }}
+
+    public enum NodeType
+    {{
+        Parent,
+        Leaf,
+    }}
+}}
+";
+
+            var compilation = CreateCompilation(source);
+
+            compilation.VerifyDiagnostics();
+        }
+
+        [WorkItem(61171, "https://github.com/dotnet/roslyn/issues/61171")]
+        [Theory]
+        [InlineData("dynamic", "object")]
+        [InlineData("(int a, int b)", "(int, int)")]
+        public void WorkItem61171_DynamicObjectTuple(string inheritedArgument, string propertyArgument)
+        {
+            string source = $@"
+public class Tree<TValue>
+{{
+    public enum NodeType
+    {{
+        Parent,
+        Leaf,
+    }}
+}}
+
+public class Tree1 : Tree<{inheritedArgument}>
+{{
+}}
+
+public class Tree2 : Tree1
+{{
+    public sealed class LeafNode
+    {{
+        public Tree<{propertyArgument}>.NodeType NodeType => NodeType.Leaf;
+    }}
+}}
+";
+
+            var compilation = CreateCompilation(source);
+
+            compilation.VerifyDiagnostics();
+        }
+
+        [WorkItem(61171, "https://github.com/dotnet/roslyn/issues/61171")]
+        [Fact]
+        public void WorkItem61171_ModoptObject()
+        {
+            string genericTreeDefinitionSource = @"
+public class Tree2 : Tree1
+{
+    public sealed class LeafNode
+    {
+        public Tree<dynamic>.NodeType NodeType => NodeType.Leaf;
+    }
+}
+";
+
+            string implementingTreeWithModoptObjectILSource = @"
+.class public auto ansi beforefieldinit Tree`1<class TValue>
+    extends [mscorlib]System.Object
+{
+    // Nested Types
+    .class nested public auto ansi sealed NodeType<class TValue>
+        extends [mscorlib]System.Enum
+    {
+        // Fields
+        .field public specialname rtspecialname int32 value__
+        .field public static literal valuetype Tree`1/NodeType<!TValue> Parent = int32(0)
+        .field public static literal valuetype Tree`1/NodeType<!TValue> Leaf = int32(1)
+
+    } // end of class NodeType
+
+
+    // Methods
+    .method public hidebysig specialname rtspecialname 
+        instance void .ctor () cil managed 
+    {
+        ldarg.0
+        call instance void [mscorlib]System.Object::.ctor()
+        ret
+    } // end of method Tree`1::.ctor
+
+} // end of class Tree`1
+
+.class public auto ansi beforefieldinit Tree1
+    extends class Tree`1<object modopt(object)>
+{
+    // Methods
+    .method public hidebysig specialname rtspecialname 
+        instance void .ctor () cil managed 
+    {
+        ldarg.0
+        call instance void class Tree`1<object>::.ctor()
+        ret
+    } // end of method Tree1::.ctor
+
+} // end of class Tree1
+";
+
+            var compilation = CreateCompilationWithIL(genericTreeDefinitionSource, implementingTreeWithModoptObjectILSource);
+
+            compilation.VerifyDiagnostics();
+        }
     }
 }