#1349: Fix type substitution for members of unknown generic types (due to unresolved references)

Also, assume that unknown inputs to ldfld are temporaries, not unmanaged pointers.
This avoids emitting weird pointer casts when accessing fields on unresolved value types.

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -1187,14 +1187,14 @@ namespace ICSharpCode.Decompiler.IL
 					return Pop(StackType.O);
 				case false:
 					// field of value type: ldfld can handle temporaries
-					if (PeekStackType() == StackType.O)
+					if (PeekStackType() == StackType.O || PeekStackType() == StackType.Unknown)
 						return new AddressOf(Pop());
 					else
 						return PopPointer();
 				default:
 					// field in unresolved type
-					if (PeekStackType() == StackType.O)
+					if (PeekStackType() == StackType.O || PeekStackType() == StackType.Unknown)
-						return Pop(StackType.O);
+						return Pop();
 					else
 						return PopPointer();
 			}

ICSharpCode.Decompiler/IL/Instructions/LdFlda.cs

@@ -36,7 +36,9 @@ namespace ICSharpCode.Decompiler.IL
 					break;
 				case null:
 					// field of unresolved type
-					Debug.Assert(target.ResultType == StackType.O || target.ResultType == StackType.I || target.ResultType == StackType.Ref);
+					Debug.Assert(target.ResultType == StackType.O || target.ResultType == StackType.I
+						|| target.ResultType == StackType.Ref || target.ResultType == StackType.Unknown,
+						"Field of unresolved type with invalid target");
 					break;
 			}
 		}

ICSharpCode.Decompiler/TypeSystem/MetadataModule.cs

@@ -477,7 +477,9 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					typeParameters.Add(new DefaultTypeParameter(m, i));
 				}
 				m.TypeParameters = typeParameters;
-				substitution = new TypeParameterSubstitution(null, typeParameters);
+				substitution = new TypeParameterSubstitution(declaringType.TypeArguments, typeParameters);
+			} else if (declaringType.TypeArguments.Count > 0) {
+				substitution = declaringType.GetSubstitution();
 			}
 			var parameters = new List<IParameter>();
 			for (int i = 0; i < signature.RequiredParameterCount; i++) {
@@ -553,6 +555,10 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			var field = declaringType.GetFields(f => f.Name == name && CompareTypes(f.ReturnType, signature),
 				GetMemberOptions.IgnoreInheritedMembers).FirstOrDefault();
 			if (field == null) {
+				// If it's a field in a generic type, we need to substitute the type arguments:
+				if (declaringType.TypeArguments.Count > 0) {
+					signature = signature.AcceptVisitor(declaringType.GetSubstitution());
+				}
 				field = new FakeField(Compilation) {
 					ReturnType = signature,
 					Name = name,