Fix crash in dataclass brain

ChangeLog

@@ -17,6 +17,9 @@ What's New in astroid 2.12.7?
 =============================
 Release date: TBA
 
+* Fixed a crash in the ``dataclass`` brain for uninferable bases.
+
+  Closes PyCQA/pylint#7418
 
 
 What's New in astroid 2.12.6?

astroid/brain/brain_dataclasses.py

@@ -231,7 +231,9 @@ def _generate_dataclass_init(
             assignments.append(assignment_str)
 
     try:
-        base: ClassDef = next(next(iter(node.bases)).infer())
+        base = next(next(iter(node.bases)).infer())
+        if not isinstance(base, ClassDef):
+            raise InferenceError
         base_init: FunctionDef | None = base.locals["__init__"][0]
     except (StopIteration, InferenceError, KeyError):
         base_init = None

tests/unittest_brain_dataclasses.py

@@ -824,3 +824,26 @@ class Dee(Cee):
             "ee",
         ]
         assert [a.name for a in dee_init.args.kwonlyargs] == []
+
+
+def test_dataclass_with_unknown_base() -> None:
+    """Regression test for dataclasses with unknown base classes.
+
+    Reported in https://github.com/PyCQA/pylint/issues/7418
+    """
+    node = astroid.extract_node(
+        """
+    import dataclasses
+
+    from unknown import Unknown
+
+
+    @dataclasses.dataclass
+    class MyDataclass(Unknown):
+        pass
+
+    MyDataclass()
+    """
+    )
+
+    assert next(node.infer())