fix(annotable): allow optional arguments at any position

fixes ibis-project#3730

ibis/common/grounds.py

@@ -103,18 +103,23 @@ def __new__(metacls, clsname, bases, dct):
 
         # mandatory fields without default values must preceed the optional
         # ones in the function signature, the partial ordering will be kept
-        new_params, inherited_params, optional_inherited_params = [], [], []
+        new_args, new_kwargs = [], []
+        inherited_args, inherited_kwargs = [], []
+
         for name, param in params.items():
             if name in inherited:
                 if param.default is EMPTY:
-                    inherited_params.append(param)
+                    inherited_args.append(param)
                 else:
-                    optional_inherited_params.append(param)
+                    inherited_kwargs.append(param)
             else:
-                new_params.append(param)
+                if param.default is EMPTY:
+                    new_args.append(param)
+                else:
+                    new_kwargs.append(param)
 
         signature = inspect.Signature(
-            inherited_params + new_params + optional_inherited_params
+            inherited_args + new_args + new_kwargs + inherited_kwargs
         )
 
         attribs["__slots__"] = tuple(slots)

ibis/common/tests/test_grounds.py

@@ -192,6 +192,24 @@ class NoHooves(Farm):
     assert g1.goats == 0
 
 
+def test_keyword_argument_reordering():
+    class Alpha(Annotable):
+        a = IsInt
+        b = IsInt
+
+    class Beta(Alpha):
+        c = IsInt
+        d = Optional(IsInt, default=0)
+        e = IsInt
+
+    obj = Beta(1, 2, 3, 4)
+    assert obj.a == 1
+    assert obj.b == 2
+    assert obj.c == 3
+    assert obj.e == 4
+    assert obj.d == 0
+
+
 def test_not_copy_default():
     default = tuple()