Handle generic parameter types as return types of builtins in DocBuilder (#1046)

* Handle generic parameter types as return types of builtins in DocBuilder

* Fix handling of by-refs of generic types

* Enable nullable annotations in DynamicHelpers

* Undo changes to PythonType

* Support generic parameter types by PythonType

Author: BCSharp

Src/IronPython/Runtime/Types/DocBuilder.cs

@@ -305,7 +305,7 @@ public static OverloadDoc GetOverloadDoc(MethodBase info, string name, int endPa
                 paramDoc.Add(
                     new ParameterDoc(
                         pi.Name ?? "",  // manufactured methods, such as string[].ctor(int) can have no parameter names.
-                        pi.ParameterType.IsGenericParameter ? pi.ParameterType.Name : GetPythonTypeName(pi.ParameterType),
+                        GetPythonTypeName(pi.ParameterType),
                         paramDocString,
                         flags
                     )
@@ -402,6 +402,10 @@ private static string GetPythonTypeName(Type type) {
                 type = type.GetElementType();
             }
 
+            if (type.IsGenericParameter) {
+                return type.Name;
+            }
+
             return DynamicHelpers.GetPythonTypeFromType(type).Name;
         }
 

Src/IronPython/Runtime/Types/DynamicHelpers.cs

@@ -2,7 +2,10 @@
 // The .NET Foundation licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
+
 using Microsoft.Scripting;
 using Microsoft.Scripting.Generation;
 using Microsoft.Scripting.Utils;
@@ -17,14 +20,14 @@ public static class DynamicHelpers {
             return PythonType.GetPythonType(type);
         }
 
-        public static PythonType GetPythonType(object o) {
+        public static PythonType GetPythonType(object? o) {
             if (o is IPythonObject dt) return dt.PythonType;
 
             return GetPythonTypeFromType(CompilerHelpers.GetType(o));
         }
 
-        public static ReflectedEvent.BoundEvent MakeBoundEvent(ReflectedEvent eventObj, object instance, Type type) {
-            return new ReflectedEvent.BoundEvent(eventObj, instance, DynamicHelpers.GetPythonTypeFromType(type));
+        public static ReflectedEvent.BoundEvent MakeBoundEvent(ReflectedEvent eventObj, object? instance, Type type) {
+            return new ReflectedEvent.BoundEvent(eventObj, instance, GetPythonTypeFromType(type));
         }
     }
 }

Src/IronPython/Runtime/Types/PythonType.cs

@@ -764,7 +764,7 @@ internal IList<PythonType> ResolutionOrder {
         /// <summary>
         /// Gets the dynamic type that corresponds with the provided static type. 
         /// 
-        /// Returns null if no type is available.  TODO: In the future this will
+        /// TODO: In the future this will
         /// always return a PythonType created by the DLR.
         /// </summary>
         /// <param name="type"></param>
@@ -777,7 +777,7 @@ internal IList<PythonType> ResolutionOrder {
                     if (!_pythonTypes.TryGetValue(type, out res)) {
                         res = new PythonType(type);
 
-                        _pythonTypes.Add(type, res);
+                       _pythonTypes.Add(type, res);
                     }
                 }
             }
@@ -2325,7 +2325,17 @@ private void AddSystemInterfaces(List<PythonType> mro) {
             lock (_bases) {
                 _bases = bases;
             }
-            
+
+            if (_underlyingSystemType.IsGenericParameter) {
+                // add all interfaces into the MRO
+                foreach (Type t in interfaces) {
+                    Debug.Assert(t.IsInterface);
+
+                    mro.Add(DynamicHelpers.GetPythonTypeFromType(t));
+                }
+                return; // end of story for generic parameter types
+            }
+
             foreach (Type iface in interfaces) {
 #if NET46
                 // causes failures on Mono: https://github.com/mono/mono/issues/14712