Improve "No method matches given arguments" message with more details (#900)

lostmsu · filmor · commit df0574db5520 · 2019-06-28T07:36:30.000+02:00
* generate more useful message, when a .NET overload can't be found, that matches Python parameter types * provide detailed error message, when an overload can't be found when calling C# from Python Related: #811, #265, #782
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -13,6 +13,8 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 
 ### Changed
 
+-   Added argument types information to "No method matches given arguments" message
+
 ### Fixed
 
 ## [2.4.0][]
diff --git a/src/embed_tests/TestCallbacks.cs b/src/embed_tests/TestCallbacks.cs
@@ -0,0 +1,35 @@
+using System;
+
+using NUnit.Framework;
+using Python.Runtime;
+
+namespace Python.EmbeddingTest {
+    using Runtime = Python.Runtime.Runtime;
+
+    public class TestCallbacks {
+        [OneTimeSetUp]
+        public void SetUp() {
+            PythonEngine.Initialize();
+        }
+
+        [OneTimeTearDown]
+        public void Dispose() {
+            PythonEngine.Shutdown();
+        }
+
+        [Test]
+        public void TestNoOverloadException() {
+            int passed = 0;
+            var aFunctionThatCallsIntoPython = new Action<int>(value => passed = value);
+            using (Py.GIL()) {
+                dynamic callWith42 = PythonEngine.Eval("lambda f: f([42])");
+                var error =  Assert.Throws<PythonException>(() => callWith42(aFunctionThatCallsIntoPython.ToPython()));
+                Assert.AreEqual("TypeError", error.PythonTypeName);
+                string expectedArgTypes = Runtime.IsPython2
+                    ? "(<type 'list'>)"
+                    : "(<class 'list'>)";
+                StringAssert.EndsWith(expectedArgTypes, error.Message);
+            }
+        }
+    }
+}
diff --git a/src/runtime/methodbinder.cs b/src/runtime/methodbinder.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections;
 using System.Reflection;
+using System.Text;
 
 namespace Python.Runtime
 {
@@ -555,12 +556,36 @@ internal virtual IntPtr Invoke(IntPtr inst, IntPtr args, IntPtr kw, MethodBase i
 
             if (binding == null)
             {
-                var value = "No method matches given arguments";
+                var value = new StringBuilder("No method matches given arguments");
                 if (methodinfo != null && methodinfo.Length > 0)
                 {
-                    value += $" for {methodinfo[0].Name}";
+                    value.Append($" for {methodinfo[0].Name}");
                 }
-                Exceptions.SetError(Exceptions.TypeError, value);
+
+                long argCount = Runtime.PyTuple_Size(args);
+                value.Append(": (");
+                for(long argIndex = 0; argIndex < argCount; argIndex++) {
+                    var arg = Runtime.PyTuple_GetItem(args, argIndex);
+                    if (arg != IntPtr.Zero) {
+                        var type = Runtime.PyObject_Type(arg);
+                        if (type != IntPtr.Zero) {
+                            try {
+                                var description = Runtime.PyObject_Unicode(type);
+                                if (description != IntPtr.Zero) {
+                                    value.Append(Runtime.GetManagedString(description));
+                                    Runtime.XDecref(description);
+                                }
+                            } finally {
+                                Runtime.XDecref(type);
+                            }
+                        }
+                    }
+
+                    if (argIndex + 1 < argCount)
+                        value.Append(", ");
+                }
+                value.Append(')');
+                Exceptions.SetError(Exceptions.TypeError, value.ToString());
                 return IntPtr.Zero;
             }
 
