Clarification on non-Module roots (#2536)

* remove last instances of Unknown parents (and None parents in tests)

It's a part of the campaign to get rid of non-module roots

* assert that the root() is always a Module

The nodes are often created in an ad-hoc way, and their parent is not
   always set. We can't control for that invariant fully in the
   constructor, since the parent is sometimes set outside of the
   constructor. The previous commits did their best to clean up such
   situations, but let's add an assert just in case.

astroid/brain/brain_argparse.py

@@ -21,7 +21,7 @@ def infer_namespace(node, context: InferenceContext | None = None):
         "Namespace",
         lineno=node.lineno,
         col_offset=node.col_offset,
-        parent=AstroidManager().adhoc_module,  # this class is not real
+        parent=AstroidManager().synthetic_root,  # this class is not real
         end_lineno=node.end_lineno,
         end_col_offset=node.end_col_offset,
     )

astroid/brain/brain_builtin_inference.py

@@ -165,7 +165,7 @@ def _extend_builtins(class_transforms):
 
 def on_bootstrap():
     """Called by astroid_bootstrapping()."""
-    AstroidManager().cache_module(build_module("__astroid_adhoc"))
+    AstroidManager().cache_module(build_module("__astroid_synthetic"))
 
     _extend_builtins(
         {
@@ -653,7 +653,7 @@ def infer_property(
         # node.frame. It's somewhere in the builtins module, but we are special
         # casing it for each "property()" call, so we are making up the
         # definition on the spot, ad-hoc.
-        parent=AstroidManager().adhoc_module,
+        parent=AstroidManager().synthetic_root,
     )
     prop_func.postinit(
         body=[],

astroid/brain/brain_namedtuple_enum.py

@@ -194,7 +194,7 @@ def infer_named_tuple(
     """Specific inference function for namedtuple Call node."""
     tuple_base: nodes.Name = _extract_single_node("tuple")
     class_node, name, attributes = infer_func_form(
-        node, tuple_base, parent=AstroidManager().adhoc_module, context=context
+        node, tuple_base, parent=AstroidManager().synthetic_root, context=context
     )
 
     call_site = arguments.CallSite.from_call(node, context=context)
@@ -360,7 +360,7 @@ def value(self):
     class_node = infer_func_form(
         node,
         enum_meta,
-        parent=AstroidManager().adhoc_module,
+        parent=AstroidManager().synthetic_root,
         context=context,
         enum=True,
     )[0]

astroid/manager.py

@@ -116,8 +116,8 @@ def builtins_module(self) -> nodes.Module:
         return self.astroid_cache["builtins"]
 
     @property
-    def adhoc_module(self) -> nodes.Module:
-        return self.astroid_cache["__astroid_adhoc"]
+    def synthetic_root(self) -> nodes.Module:
+        return self.astroid_cache["__astroid_synthetic"]
 
     @property
     def prefer_stubs(self) -> bool:

astroid/nodes/node_ng.py

@@ -21,7 +21,7 @@
     overload,
 )
 
-from astroid import util
+from astroid import nodes, util
 from astroid.context import InferenceContext
 from astroid.exceptions import (
     AstroidError,
@@ -43,7 +43,6 @@
 
 
 if TYPE_CHECKING:
-    from astroid import nodes
     from astroid.nodes import _base_nodes
 
 
@@ -332,11 +331,13 @@ def root(self) -> nodes.Module:
         :returns: The root node.
         """
         if not (parent := self.parent):
-            return self  # type: ignore[return-value] # Only 'Module' does not have a parent node.
+            assert isinstance(self, nodes.Module)
+            return self
 
         while parent.parent:
             parent = parent.parent
-        return parent  # type: ignore[return-value] # Only 'Module' does not have a parent node.
+        assert isinstance(parent, nodes.Module)
+        return parent
 
     def child_sequence(self, child):
         """Search for the sequence that contains this child.

astroid/nodes/scoped_nodes/scoped_nodes.py

@@ -44,7 +44,6 @@
     Arguments,
     Const,
     NodeNG,
-    Unknown,
     _base_nodes,
     const_factory,
     node_classes,
@@ -1603,7 +1602,7 @@ def infer_call_result(
                     col_offset=0,
                     end_lineno=0,
                     end_col_offset=0,
-                    parent=AstroidManager().adhoc_module,
+                    parent=AstroidManager().synthetic_root,
                 )
                 new_class.hide = True
                 new_class.postinit(
@@ -2037,7 +2036,7 @@ def _infer_type_call(self, caller, context):
             col_offset=0,
             end_lineno=0,
             end_col_offset=0,
-            parent=Unknown(),
+            parent=caller.parent,
         )
 
         # Get the bases of the class.
@@ -2071,7 +2070,6 @@ def _infer_type_call(self, caller, context):
                 if isinstance(attr, node_classes.Const) and isinstance(attr.value, str):
                     result.locals[attr.value] = [value]
 
-        result.parent = caller.parent
         return result
 
     def infer_call_result(

astroid/objects.py

@@ -279,7 +279,7 @@ def __init__(self, call, name=None, lineno=None, col_offset=None, parent=None):
             name,
             lineno=lineno,
             col_offset=col_offset,
-            parent=AstroidManager().adhoc_module,
+            parent=AstroidManager().synthetic_root,
             end_col_offset=0,
             end_lineno=0,
         )

astroid/raw_building.py

@@ -670,9 +670,8 @@ def _astroid_bootstrapping() -> None:
             col_offset=0,
             end_lineno=0,
             end_col_offset=0,
-            parent=nodes.Unknown(),
+            parent=astroid_builtin,
         )
-        _UnionTypeType.parent = astroid_builtin
         union_type_doc_node = (
             nodes.Const(value=types.UnionType.__doc__)
             if types.UnionType.__doc__
@@ -707,9 +706,8 @@ def _astroid_bootstrapping() -> None:
                 col_offset=0,
                 end_lineno=0,
                 end_col_offset=0,
-                parent=nodes.Unknown(),
+                parent=astroid_builtin,
             )
-            klass.parent = astroid_builtin
             doc = _type.__doc__ if isinstance(_type.__doc__, str) else None
             klass.postinit(
                 bases=[],

tests/test_nodes.py

@@ -37,6 +37,7 @@
     ParentMissingError,
     StatementMissing,
 )
+from astroid.manager import AstroidManager
 from astroid.nodes.node_classes import (
     AssignAttr,
     AssignName,
@@ -1960,7 +1961,9 @@ def test_str_repr_no_warnings(node):
         if name == "self":
             continue
 
-        if "int" in param_type.annotation:
+        if name == "parent" and "NodeNG" in param_type.annotation:
+            args[name] = AstroidManager().synthetic_root
+        elif "int" in param_type.annotation:
             args[name] = random.randint(0, 50)
         elif (
             "NodeNG" in param_type.annotation