Show kwargs in failed method invocation

With the previous commit, output can be very confusing because you only
see positional arguments in the "invoked with" line, but you can have a
failure from kwargs as well (in particular, when a value is invalidly
specified via both via positional and kwargs).  This commits adds
kwargs to the output, and updates the associated tests to match.

include/pybind11/pybind11.h

@@ -650,11 +650,26 @@ protected:
             }
             msg += "\nInvoked with: ";
             auto args_ = reinterpret_borrow<tuple>(args_in);
+            bool some_args = false;
             for (size_t ti = overloads->is_constructor ? 1 : 0; ti < args_.size(); ++ti) {
+                if (!some_args) some_args = true;
+                else msg += ", ";
                 msg += pybind11::repr(args_[ti]);
-                if ((ti + 1) != args_.size() )
-                    msg += ", ";
             }
+            if (kwargs_in) {
+                auto kwargs = reinterpret_borrow<dict>(kwargs_in);
+                if (kwargs.size() > 0) {
+                    if (some_args) msg += "; ";
+                    msg += "kwargs: ";
+                    bool first = true;
+                    for (auto kwarg : kwargs) {
+                        if (first) first = false;
+                        else msg += ", ";
+                        msg += pybind11::str("{}={!r}").format(kwarg.first, kwarg.second);
+                    }
+                }
+            }
+
             PyErr_SetString(PyExc_TypeError, msg.c_str());
             return nullptr;
         } else if (!result) {

tests/test_kwargs_and_defaults.py

@@ -34,12 +34,8 @@ def test_named_arguments(msg):
     with pytest.raises(TypeError) as excinfo:
         # noinspection PyArgumentList
         kw_func2(x=5, y=10, z=12)
-    assert msg(excinfo.value) == """
-        kw_func2(): incompatible function arguments. The following argument types are supported:
-            1. (x: int=100, y: int=200) -> str
-
-        Invoked with:
-    """
+    assert excinfo.match(
+        r'(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$)){3}$')
 
     assert kw_func4() == "{13 17}"
     assert kw_func4(myList=[1, 2, 3]) == "{1 2 3}"
@@ -74,7 +70,7 @@ def test_mixed_args_and_kwargs(msg):
             1. (arg0: int, arg1: float, *args) -> tuple
 
         Invoked with: 1
-    """  # noqa: E501
+    """  # noqa: E501 line too long
     with pytest.raises(TypeError) as excinfo:
         assert mpa()
     assert msg(excinfo.value) == """
@@ -82,7 +78,7 @@ def test_mixed_args_and_kwargs(msg):
             1. (arg0: int, arg1: float, *args) -> tuple
 
         Invoked with:
-    """  # noqa: E501
+    """  # noqa: E501 line too long
 
     assert mpk(-2, 3.5, pi=3.14159, e=2.71828) == (-2, 3.5, {'e': 2.71828, 'pi': 3.14159})
     assert mpak(7, 7.7, 7.77, 7.777, 7.7777, minusseven=-7) == (
@@ -93,14 +89,20 @@ def test_mixed_args_and_kwargs(msg):
     assert mpakd(k=42) == (1, 3.14159, (), {'k': 42})
     assert mpakd(1, 1, 2, 3, 5, 8, then=13, followedby=21) == (
         1, 1, (2, 3, 5, 8), {'then': 13, 'followedby': 21})
-    # Arguments specified both positionally and via kwargs is an error:
+    # Arguments specified both positionally and via kwargs should fail:
     with pytest.raises(TypeError) as excinfo:
         assert mpakd(1, i=1)
     assert msg(excinfo.value) == """
-        mixed_plus_args_kwargs_defaults(): got multiple values for argument 'i'
-    """
+        mixed_plus_args_kwargs_defaults(): incompatible function arguments. The following argument types are supported:
+            1. (i: int=1, j: float=3.14159, *args, **kwargs) -> tuple
+
+        Invoked with: 1; kwargs: i=1
+    """  # noqa: E501 line too long
     with pytest.raises(TypeError) as excinfo:
         assert mpakd(1, 2, j=1)
     assert msg(excinfo.value) == """
-        mixed_plus_args_kwargs_defaults(): got multiple values for argument 'j'
-    """
+        mixed_plus_args_kwargs_defaults(): incompatible function arguments. The following argument types are supported:
+            1. (i: int=1, j: float=3.14159, *args, **kwargs) -> tuple
+
+        Invoked with: 1, 2; kwargs: j=1
+    """  # noqa: E501 line too long