Support match_args in cdef dataclasses

Cython/Compiler/Dataclass.py

@@ -299,7 +299,7 @@ def handle_cclass_dataclass(node, dataclass_args, analyse_decs_transform):
     # default argument values from https://docs.python.org/3/library/dataclasses.html
     kwargs = dict(init=True, repr=True, eq=True,
                   order=False, unsafe_hash=False,
-                  frozen=False, kw_only=False)
+                  frozen=False, kw_only=False, match_args=True)
     if dataclass_args is not None:
         if dataclass_args[0]:
             error(node.pos, "cython.dataclasses.dataclass takes no positional arguments")
@@ -330,7 +330,7 @@ def handle_cclass_dataclass(node, dataclass_args, analyse_decs_transform):
           for k, v in kwargs.items() ] +
         [ (ExprNodes.IdentifierStringNode(node.pos, value=EncodedString(k)),
            ExprNodes.BoolNode(node.pos, value=v))
-          for k, v in [('kw_only', kw_only), ('match_args', False),
+          for k, v in [('kw_only', kw_only),
                        ('slots', False), ('weakref_slot', False)]
         ])
     dataclass_params = make_dataclass_call_helper(
@@ -347,6 +347,7 @@ def handle_cclass_dataclass(node, dataclass_args, analyse_decs_transform):
 
     code = TemplateCode()
     generate_init_code(code, kwargs['init'], node, fields, kw_only)
+    generate_match_args(code, kwargs['match_args'], node, fields, kw_only)
     generate_repr_code(code, kwargs['repr'], node, fields)
     generate_eq_code(code, kwargs['eq'], node, fields)
     generate_order_code(code, kwargs['order'], node, fields)
@@ -469,6 +470,27 @@ def generate_init_code(code, init, node, fields, kw_only):
     function_start_point.add_code_line(u"def __init__(%s):" % args)
 
 
+def generate_match_args(code, match_args, node, fields, global_kw_only):
+    """
+    Generates a tuple containing what would be the positional args to __init__
+
+    Note that this is generated even if the user overrides init
+    """
+    if not match_args or node.scope.lookup_here("__match_args__"):
+        return
+    positional_arg_names = []
+    for field_name, field in fields.items():
+        # TODO hasattr and global_kw_only can be removed once full kw_only support is added
+        field_is_kw_only = global_kw_only or (
+            hasattr(field, 'kw_only') and field.kw_only.value
+        )
+        if not field_is_kw_only:
+            positional_arg_names.append(repr(field_name))
+    positional_arg_names.append("")  # finish the tuple with a comma
+    args = u", ".join(positional_arg_names)
+    code.add_code_line("__match_args__ = (%s)" % args)
+
+
 def generate_repr_code(code, repr, node, fields):
     """
     The core of the CPython implementation is just:

Tools/make_dataclass_tests.py

@@ -58,6 +58,7 @@
         ("TestCase", "test_class_attrs"),
         ("TestCase", "test_hash_field_rules"),
         ("TestStringAnnotations",),  # almost all the texts here use local variables
+        ("TestMatchArgs", "test_explicit_match_args"),
         # Currently unsupported
         # =====================
         (
@@ -68,7 +69,6 @@
         ("TestCase", "test_missing_default"),  # MISSING
         ("TestCase", "test_missing_repr"),  # MISSING
         ("TestSlots",),  # __slots__ isn't understood
-        ("TestMatchArgs",),
         ("TestKeywordArgs", "test_field_marked_as_kwonly"),
         ("TestKeywordArgs", "test_match_args"),
         ("TestKeywordArgs", "test_KW_ONLY"),

tests/run/test_dataclasses.pyx

@@ -607,6 +607,45 @@ class C_TestReplace_test_recursive_repr_misc_attrs:
     f: object
     g: int
 
+@dataclass
+@cclass
+class C_TestMatchArgs_test_match_args:
+    a: int
+
+@dataclass(repr=False, eq=False, init=False)
+@cclass
+class X_TestMatchArgs_test_bpo_43764:
+    a: int
+    b: int
+    c: int
+
+@dataclass(match_args=False)
+@cclass
+class X_TestMatchArgs_test_match_args_argument:
+    a: int
+
+@dataclass(match_args=False)
+@cclass
+class Y_TestMatchArgs_test_match_args_argument:
+    a: int
+    __match_args__ = ('b',)
+
+@dataclass(match_args=False)
+@cclass
+class Z_TestMatchArgs_test_match_args_argument(Y_TestMatchArgs_test_match_args_argument):
+    z: int
+
+@dataclass
+@cclass
+class A_TestMatchArgs_test_match_args_argument:
+    a: int
+    z: int
+
+@dataclass(match_args=False)
+@cclass
+class B_TestMatchArgs_test_match_args_argument(A_TestMatchArgs_test_match_args_argument):
+    b: int
+
 class CustomError(Exception):
     pass
 
@@ -1180,6 +1219,27 @@ class TestReplace(unittest.TestCase):
 class TestAbstract(unittest.TestCase):
     pass
 
+class TestMatchArgs(unittest.TestCase):
+
+    def test_match_args(self):
+        C = C_TestMatchArgs_test_match_args
+        self.assertEqual(C(42).__match_args__, ('a',))
+
+    def test_bpo_43764(self):
+        X = X_TestMatchArgs_test_bpo_43764
+        self.assertEqual(X.__match_args__, ('a', 'b', 'c'))
+
+    def test_match_args_argument(self):
+        X = X_TestMatchArgs_test_match_args_argument
+        self.assertNotIn('__match_args__', X.__dict__)
+        Y = Y_TestMatchArgs_test_match_args_argument
+        self.assertEqual(Y.__match_args__, ('b',))
+        Z = Z_TestMatchArgs_test_match_args_argument
+        self.assertEqual(Z.__match_args__, ('b',))
+        A = A_TestMatchArgs_test_match_args_argument
+        B = B_TestMatchArgs_test_match_args_argument
+        self.assertEqual(B.__match_args__, ('a', 'z'))
+
 class TestKeywordArgs(unittest.TestCase):
     pass
 if __name__ == '__main__':