[fix] Fix a crash when the root of a node is not a module but is unknown (#2739)

Closes #2672

Author: Pierre-Sassoulas

ChangeLog

@@ -37,6 +37,10 @@ What's New in astroid 3.3.11?
 =============================
 Release date: TBA
 
+* Fix a crash when the root of a node is not a module but is unknown.
+
+  Closes #2672
+
 * Fix a crash when parsing an empty arbitrary expression with ``extract_node`` (``extract_node("__()")``).
 
   Closes #2734

astroid/nodes/node_ng.py

@@ -309,13 +309,13 @@ def scope(self) -> nodes.LocalsDictNodeNG:
             raise ParentMissingError(target=self)
         return self.parent.scope()
 
-    def root(self) -> nodes.Module:
+    def root(self) -> nodes.Module | nodes.Unknown:
         """Return the root node of the syntax tree.
 
         :returns: The root node.
         """
         if not (parent := self.parent):
-            assert isinstance(self, nodes.Module)
+            assert isinstance(self, (nodes.Module, nodes.Unknown))
             return self
 
         while parent.parent:

tests/test_regrtest.py

@@ -500,6 +500,21 @@ def _get_option(self, option):
     assert node.inferred()[0].value == "mystr"
 
 
+def test_regression_root_is_not_a_module() -> None:
+    """Regression test for #2672."""
+    node: nodes.Attribute = _extract_single_node(
+        textwrap.dedent(
+            """
+        a=eval.__get__(1).__gt__
+
+        @a
+        class c: ...
+        """
+        )
+    )
+    assert node.name == "c"
+
+
 def test_regression_no_crash_during_build() -> None:
     node: nodes.Attribute = extract_node("__()")
     assert node.args == []