Fixed the __init__ of dataclassess with multiple inheritance

ChangeLog

@@ -17,6 +17,10 @@ What's New in astroid 2.12.9?
 =============================
 Release date: TBA
 
+* Fixed creation of the ``__init__`` of ``dataclassess`` with multiple inheritance.
+
+  Closes PyCQA/pylint#7427
+
 * Fixed a crash on ``namedtuples`` that use ``typename`` to specify their name.
 
   Closes PyCQA/pylint#7429

astroid/brain/brain_dataclasses.py

@@ -177,6 +177,45 @@ def _check_generate_dataclass_init(node: nodes.ClassDef) -> bool:
     )
 
 
+def _find_arguments_from_base_classes(
+    node: nodes.ClassDef, skippable_names: set[str]
+) -> tuple[str, str]:
+    """Iterate through all bases and add them to the list of arguments to add to the init."""
+    prev_pos_only = ""
+    prev_kw_only = ""
+    for base in node.mro():
+        if not base.is_dataclass:
+            continue
+        try:
+            base_init: nodes.FunctionDef = base.locals["__init__"][0]
+        except KeyError:
+            continue
+
+        # Skip the self argument and check for duplicate arguments
+        arguments = base_init.args.format_args(skippable_names=skippable_names)
+        try:
+            new_prev_pos_only, new_prev_kw_only = arguments.split("*, ")
+        except ValueError:
+            new_prev_pos_only, new_prev_kw_only = arguments, ""
+
+        if new_prev_pos_only:
+            # The split on '*, ' can crete a pos_only string that consists only of a comma
+            if new_prev_pos_only == ", ":
+                new_prev_pos_only = ""
+            elif not new_prev_pos_only.endswith(", "):
+                new_prev_pos_only += ", "
+
+        # Dataclasses put last seen arguments at the front of the init
+        prev_pos_only = new_prev_pos_only + prev_pos_only
+        prev_kw_only = new_prev_kw_only + prev_kw_only
+
+        # Add arguments to skippable arguments
+        skippable_names.update(arg.name for arg in base_init.args.args)
+        skippable_names.update(arg.name for arg in base_init.args.kwonlyargs)
+
+    return prev_pos_only, prev_kw_only
+
+
 def _generate_dataclass_init(
     node: nodes.ClassDef, assigns: list[nodes.AnnAssign], kw_only_decorated: bool
 ) -> str:
@@ -228,26 +267,9 @@ def _generate_dataclass_init(
         if not init_var:
             assignments.append(assignment_str)
 
-    try:
-        base = next(next(iter(node.bases)).infer())
-        if not isinstance(base, nodes.ClassDef):
-            raise InferenceError
-        base_init: nodes.FunctionDef | None = base.locals["__init__"][0]
-    except (StopIteration, InferenceError, KeyError):
-        base_init = None
-
-    prev_pos_only = ""
-    prev_kw_only = ""
-    if base_init and base.is_dataclass:
-        # Skip the self argument and check for duplicate arguments
-        arguments = base_init.args.format_args(skippable_names=assign_names)[6:]
-        try:
-            prev_pos_only, prev_kw_only = arguments.split("*, ")
-        except ValueError:
-            prev_pos_only, prev_kw_only = arguments, ""
-
-        if prev_pos_only and not prev_pos_only.endswith(", "):
-            prev_pos_only += ", "
+    prev_pos_only, prev_kw_only = _find_arguments_from_base_classes(
+        node, set(assign_names + ["self"])
+    )
 
     # Construct the new init method paramter string
     params_string = "self, "

tests/unittest_brain_dataclasses.py

@@ -912,3 +912,135 @@ class GoodExampleClass(GoodExampleParentClass):
     good_init: bases.UnboundMethod = next(good_node.infer())
     assert bad_init.args.defaults
     assert [a.name for a in good_init.args.args] == ["self", "xyz"]
+
+
+def test_dataclass_with_multiple_inheritance() -> None:
+    """Regression test for dataclasses with multiple inheritance.
+
+    Reported in https://github.com/PyCQA/pylint/issues/7427
+    """
+    first, second, overwritten, overwriting, mixed = astroid.extract_node(
+        """
+    from dataclasses import dataclass
+
+    @dataclass
+    class BaseParent:
+        _abc: int = 1
+
+    @dataclass
+    class AnotherParent:
+        ef: int = 2
+
+    @dataclass
+    class FirstChild(BaseParent, AnotherParent):
+        ghi: int = 3
+
+    @dataclass
+    class ConvolutedParent(AnotherParent):
+        '''Convoluted Parent'''
+
+    @dataclass
+    class SecondChild(BaseParent, ConvolutedParent):
+        jkl: int = 4
+
+    @dataclass
+    class OverwritingParent:
+        ef: str = "2"
+
+    @dataclass
+    class OverwrittenChild(OverwritingParent, AnotherParent):
+        '''Overwritten Child'''
+
+    @dataclass
+    class OverwritingChild(BaseParent, AnotherParent):
+        _abc: float = 1.0
+        ef: float = 2.0
+
+    class NotADataclassParent:
+        ef: int = 2
+
+    @dataclass
+    class ChildWithMixedParents(BaseParent, NotADataclassParent):
+        ghi: int = 3
+
+    FirstChild.__init__  #@
+    SecondChild.__init__  #@
+    OverwrittenChild.__init__  #@
+    OverwritingChild.__init__  #@
+    ChildWithMixedParents.__init__  #@
+    """
+    )
+
+    first_init: bases.UnboundMethod = next(first.infer())
+    assert [a.name for a in first_init.args.args] == ["self", "ef", "_abc", "ghi"]
+    assert [a.value for a in first_init.args.defaults] == [2, 1, 3]
+
+    second_init: bases.UnboundMethod = next(second.infer())
+    assert [a.name for a in second_init.args.args] == ["self", "ef", "_abc", "jkl"]
+    assert [a.value for a in second_init.args.defaults] == [2, 1, 4]
+
+    overwritten_init: bases.UnboundMethod = next(overwritten.infer())
+    assert [a.name for a in overwritten_init.args.args] == ["self", "ef"]
+    assert [a.value for a in overwritten_init.args.defaults] == ["2"]
+
+    overwriting_init: bases.UnboundMethod = next(overwriting.infer())
+    assert [a.name for a in overwriting_init.args.args] == ["self", "_abc", "ef"]
+    assert [a.value for a in overwriting_init.args.defaults] == [1.0, 2.0]
+
+    mixed_init: bases.UnboundMethod = next(mixed.infer())
+    assert [a.name for a in mixed_init.args.args] == ["self", "_abc", "ghi"]
+    assert [a.value for a in mixed_init.args.defaults] == [1, 3]
+
+
+def test_dataclass_inits_of_non_dataclasses() -> None:
+    """Regression test for __init__ mangling for non dataclasses.
+
+    Regression test against changes tested in test_dataclass_with_multiple_inheritance
+    """
+    first, second, third = astroid.extract_node(
+        """
+    from dataclasses import dataclass
+
+    @dataclass
+    class DataclassParent:
+        _abc: int = 1
+
+
+    class NotADataclassParent:
+        ef: int = 2
+
+
+    class FirstChild(DataclassParent, NotADataclassParent):
+        ghi: int = 3
+
+
+    class SecondChild(DataclassParent, NotADataclassParent):
+        ghi: int = 3
+
+        def __init__(self, ef: int = 3):
+            self.ef = ef
+
+
+    class ThirdChild(NotADataclassParent, DataclassParent):
+        ghi: int = 3
+
+        def __init__(self, ef: int = 3):
+            self.ef = ef
+
+    FirstChild.__init__  #@
+    SecondChild.__init__  #@
+    ThirdChild.__init__  #@
+    """
+    )
+
+    first_init: bases.UnboundMethod = next(first.infer())
+    assert [a.name for a in first_init.args.args] == ["self", "_abc"]
+    assert [a.value for a in first_init.args.defaults] == [1]
+
+    second_init: bases.UnboundMethod = next(second.infer())
+    assert [a.name for a in second_init.args.args] == ["self", "ef"]
+    assert [a.value for a in second_init.args.defaults] == [3]
+
+    third_init: bases.UnboundMethod = next(third.infer())
+    assert [a.name for a in third_init.args.args] == ["self", "ef"]
+    assert [a.value for a in third_init.args.defaults] == [3]