Fix regression in the creation of the ``__init__`` of dataclasses (#1812)

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>

1 files changed, 42 insertions, 27 deletions

diff --git a/astroid/brain/brain_dataclasses.py b/astroid/brain/brain_dataclasses.py
index 264957e0..5d3c3461 100644
--- a/astroid/brain/brain_dataclasses.py
+++ b/astroid/brain/brain_dataclasses.py
@@ -181,9 +181,12 @@ 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():
+    pos_only_store: dict[str, tuple[str | None, str | None]] = {}
+    kw_only_store: dict[str, tuple[str | None, str | None]] = {}
+    # See TODO down below
+    # all_have_defaults = True
+
+    for base in reversed(node.mro()):
         if not base.is_dataclass:
             continue
         try:
@@ -191,29 +194,41 @@ def _find_arguments_from_base_classes(
         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
+        pos_only, kw_only = base_init.args._get_arguments_data()
+        for posarg, data in pos_only.items():
+            if posarg in skippable_names:
+                continue
+            # if data[1] is None:
+            #     if all_have_defaults and pos_only_store:
+            #         # TODO: This should return an Uninferable as this would raise
+            #         # a TypeError at runtime. However, transforms can't return
+            #         # Uninferables currently.
+            #         pass
+            #     all_have_defaults = False
+            pos_only_store[posarg] = data
+
+        for kwarg, data in kw_only.items():
+            if kwarg in skippable_names:
+                continue
+            kw_only_store[kwarg] = data
+
+    pos_only, kw_only = "", ""
+    for pos_arg, data in pos_only_store.items():
+        pos_only += pos_arg
+        if data[0]:
+            pos_only += ": " + data[0]
+        if data[1]:
+            pos_only += " = " + data[1]
+        pos_only += ", "
+    for kw_arg, data in kw_only_store.items():
+        kw_only += kw_arg
+        if data[0]:
+            kw_only += ": " + data[0]
+        if data[1]:
+            kw_only += " = " + data[1]
+        kw_only += ", "
+
+    return pos_only, kw_only
 
 
 def _generate_dataclass_init(
@@ -282,7 +297,7 @@ def _generate_dataclass_init(
         params_string += ", "
 
     if prev_kw_only:
-        params_string += "*, " + prev_kw_only + ", "
+        params_string += "*, " + prev_kw_only
         if kw_only_decorated:
             params_string += ", ".join(params) + ", "
     elif kw_only_decorated: