Parse default values in dataclass attributes correctly (#1771)

ChangeLog

@@ -17,7 +17,9 @@ What's New in astroid 2.12.8?
 =============================
 Release date: TBA
 
+* Fixed parsing of default values in ``dataclass`` attributes.
 
+  Closes PyCQA/pylint#7425
 
 What's New in astroid 2.12.7?
 =============================

astroid/brain/brain_dataclasses.py

@@ -242,10 +242,7 @@ def _generate_dataclass_init(
     prev_kw_only = ""
     if base_init and base.is_dataclass:
         # Skip the self argument and check for duplicate arguments
-        all_arguments = base_init.args.format_args()[6:].split(", ")
-        arguments = ", ".join(
-            i for i in all_arguments if i.split(":")[0] not in assign_names
-        )
+        arguments = base_init.args.format_args(skippable_names=assign_names)[6:]
         try:
             prev_pos_only, prev_kw_only = arguments.split("*, ")
         except ValueError:

astroid/nodes/node_classes.py

@@ -784,7 +784,7 @@ def arguments(self):
         """Get all the arguments for this node, including positional only and positional and keyword"""
         return list(itertools.chain((self.posonlyargs or ()), self.args or ()))
 
-    def format_args(self):
+    def format_args(self, *, skippable_names: set[str] | None = None) -> str:
         """Get the arguments formatted as string.
 
         :returns: The formatted arguments.
@@ -804,6 +804,7 @@ def format_args(self):
                     self.posonlyargs,
                     positional_only_defaults,
                     self.posonlyargs_annotations,
+                    skippable_names=skippable_names,
                 )
             )
             result.append("/")
@@ -813,6 +814,7 @@ def format_args(self):
                     self.args,
                     positional_or_keyword_defaults,
                     getattr(self, "annotations", None),
+                    skippable_names=skippable_names,
                 )
             )
         if self.vararg:
@@ -822,7 +824,10 @@ def format_args(self):
                 result.append("*")
             result.append(
                 _format_args(
-                    self.kwonlyargs, self.kw_defaults, self.kwonlyargs_annotations
+                    self.kwonlyargs,
+                    self.kw_defaults,
+                    self.kwonlyargs_annotations,
+                    skippable_names=skippable_names,
                 )
             )
         if self.kwarg:
@@ -929,7 +934,11 @@ def _find_arg(argname, args, rec=False):
     return None, None
 
 
-def _format_args(args, defaults=None, annotations=None):
+def _format_args(
+    args, defaults=None, annotations=None, skippable_names: set[str] | None = None
+) -> str:
+    if skippable_names is None:
+        skippable_names = set()
     values = []
     if args is None:
         return ""
@@ -939,6 +948,8 @@ def _format_args(args, defaults=None, annotations=None):
         default_offset = len(args) - len(defaults)
     packed = itertools.zip_longest(args, annotations)
     for i, (arg, annotation) in enumerate(packed):
+        if arg.name in skippable_names:
+            continue
         if isinstance(arg, Tuple):
             values.append(f"({_format_args(arg.elts)})")
         else:

tests/unittest_brain_dataclasses.py

@@ -847,3 +847,44 @@ class MyDataclass(Unknown):
     )
 
     assert next(node.infer())
+
+
+def test_dataclass_with_default_factory() -> None:
+    """Regression test for dataclasses with default values.
+
+    Reported in https://github.com/PyCQA/pylint/issues/7425
+    """
+    bad_node, good_node = astroid.extract_node(
+        """
+    from dataclasses import dataclass
+    from typing import Union
+
+    @dataclass
+    class BadExampleParentClass:
+        xyz: Union[str, int]
+
+    @dataclass
+    class BadExampleClass(BadExampleParentClass):
+        xyz: str = ""
+
+    BadExampleClass.__init__  #@
+
+    @dataclass
+    class GoodExampleParentClass:
+        xyz: str
+
+    @dataclass
+    class GoodExampleClass(GoodExampleParentClass):
+        xyz: str = ""
+
+    GoodExampleClass.__init__  #@
+    """
+    )
+
+    bad_init: bases.UnboundMethod = next(bad_node.infer())
+    assert bad_init.args.defaults
+    assert [a.name for a in bad_init.args.args] == ["self", "xyz"]
+
+    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"]