Use ReflectedTypeinstead of DeclaringType for finding the correct invocation method.

Author: ycrumeyrolle

src/System.CommandLine.Tests/Invocation/CommandHandlerTests.cs

@@ -537,5 +537,47 @@ void Execute(string fullnameOrNickname, int age)
             boundName.Should().Be("Gandalf");
             boundAge.Should().Be(425);
         }
+
+        [Theory]
+        [InlineData(typeof(ConcreteTestCommandHandler), 42)]
+        [InlineData(typeof(VirtualTestCommandHandler), 42)]
+        [InlineData(typeof(OverridenVirtualTestCommandHandler), 41)]
+        public async Task Method_invoked_is_matching_to_the_interface_implementation(Type type, int expectedResult)
+        {
+            var command = new Command("command");
+            command.Handler = CommandHandler.Create(type.GetMethod(nameof(ICommandHandler.InvokeAsync)));
+
+            var parser = new Parser(command);
+
+            int result = await parser.InvokeAsync("command", _console);
+
+            result.Should().Be(expectedResult);
+        }
+
+        public abstract class AbstractTestCommandHandler : ICommandHandler
+        {
+            public abstract Task<int> DoJobAsync();
+
+            public Task<int> InvokeAsync(InvocationContext context)
+                => DoJobAsync();
+        }
+
+        public sealed class ConcreteTestCommandHandler : AbstractTestCommandHandler
+        {
+            public override Task<int> DoJobAsync()
+                => Task.FromResult(42);
+        }
+
+        public class VirtualTestCommandHandler : ICommandHandler
+        {
+            public virtual Task<int> InvokeAsync(InvocationContext context)
+                => Task.FromResult(42);
+        }
+
+        public class OverridenVirtualTestCommandHandler : VirtualTestCommandHandler
+        {
+            public override Task<int> InvokeAsync(InvocationContext context)
+                => Task.FromResult(41);
+        }
     }
 }

src/System.CommandLine/Invocation/ModelBindingCommandHandler.cs

@@ -27,7 +27,7 @@ public ModelBindingCommandHandler(
             _handlerMethodInfo = handlerMethodInfo ?? throw new ArgumentNullException(nameof(handlerMethodInfo));
             _invocationTargetBinder = _handlerMethodInfo.IsStatic
                                           ? null
-                                          : new ModelBinder(_handlerMethodInfo.DeclaringType);
+                                          : new ModelBinder(_handlerMethodInfo.ReflectedType);
             _methodDescriptor = methodDescriptor ?? throw new ArgumentNullException(nameof(methodDescriptor));
         }