make constants have synthetic root as their parent

that fixes a bunch of tests in pylint.

We also make the synthetic root a singleton, as opposed to a module
   built in the astroid manager. That allows us to use it as a default
   value in Const constructors.

Note the changes to the test. Before, we in fact tested that constants
   don't have a parent. Is that reasonable? In fact, it seems like
   there are a variety of interpretations and we shouldn't commit to
   one by explicitly testing for a certain parent or lack thereof.

Author: temyurchenko

Diff for: 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().synthetic_root,  # this class is not real
+        parent=nodes.SYNTHETIC_ROOT,  # this class is not real
         end_lineno=node.end_lineno,
         end_col_offset=node.end_col_offset,
     )

Diff for: astroid/brain/brain_builtin_inference.py

@@ -24,7 +24,6 @@
 from astroid.inference_tip import inference_tip
 from astroid.manager import AstroidManager
 from astroid.nodes import scoped_nodes
-from astroid.raw_building import build_module
 from astroid.typing import (
     ConstFactoryResult,
     InferenceResult,
@@ -165,8 +164,6 @@ def _extend_builtins(class_transforms):
 
 def on_bootstrap():
     """Called by astroid_bootstrapping()."""
-    AstroidManager().cache_module(build_module("__astroid_synthetic"))
-
     _extend_builtins(
         {
             "bytes": partial(_extend_string_class, code=BYTES_CLASS, rvalue="b''"),
@@ -653,7 +650,7 @@ 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().synthetic_root,
+        parent=scoped_nodes.SYNTHETIC_ROOT,
     )
     prop_func.postinit(
         body=[],

Diff for: astroid/brain/brain_namedtuple_enum.py

@@ -24,6 +24,7 @@
 )
 from astroid.inference_tip import inference_tip
 from astroid.manager import AstroidManager
+from astroid.nodes.scoped_nodes.scoped_nodes import SYNTHETIC_ROOT
 
 ENUM_QNAME: Final[str] = "enum.Enum"
 TYPING_NAMEDTUPLE_QUALIFIED: Final = {
@@ -194,7 +195,7 @@ 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().synthetic_root, context=context
+        node, tuple_base, parent=SYNTHETIC_ROOT, context=context
     )
 
     call_site = arguments.CallSite.from_call(node, context=context)
@@ -360,7 +361,7 @@ def value(self):
     class_node = infer_func_form(
         node,
         enum_meta,
-        parent=AstroidManager().synthetic_root,
+        parent=SYNTHETIC_ROOT,
         context=context,
         enum=True,
     )[0]

Diff for: astroid/manager.py

@@ -115,10 +115,6 @@ def unregister_transform(self):
     def builtins_module(self) -> nodes.Module:
         return self.astroid_cache["builtins"]
 
-    @property
-    def synthetic_root(self) -> nodes.Module:
-        return self.astroid_cache["__astroid_synthetic"]
-
     @property
     def prefer_stubs(self) -> bool:
         return AstroidManager.brain["prefer_stubs"]

Diff for: astroid/nodes/__init__.py

@@ -93,6 +93,7 @@
     unpack_infer,
 )
 from astroid.nodes.scoped_nodes import (
+    SYNTHETIC_ROOT,
     AsyncFunctionDef,
     ClassDef,
     ComprehensionScope,
@@ -276,6 +277,7 @@
     "Position",
     "Raise",
     "Return",
+    "SYNTHETIC_ROOT",
     "Set",
     "SetComp",
     "Slice",

Diff for: astroid/nodes/node_classes.py

@@ -46,6 +46,7 @@
 from astroid.nodes import _base_nodes
 from astroid.nodes.const import OP_PRECEDENCE
 from astroid.nodes.node_ng import NodeNG
+from astroid.nodes.scoped_nodes import SYNTHETIC_ROOT
 from astroid.typing import (
     ConstFactoryResult,
     InferenceErrorInfo,
@@ -2038,7 +2039,7 @@ def __init__(
         value: Any,
         lineno: int | None = None,
         col_offset: int | None = None,
-        parent: NodeNG | None = None,
+        parent: NodeNG = SYNTHETIC_ROOT,
         kind: str | None = None,
         *,
         end_lineno: int | None = None,
@@ -2550,7 +2551,7 @@ def __init__(
         self,
         lineno: None = None,
         col_offset: None = None,
-        parent: None = None,
+        parent: NodeNG = SYNTHETIC_ROOT,
         *,
         end_lineno: None = None,
         end_col_offset: None = None,
@@ -5535,7 +5536,7 @@ def const_factory(value: Any) -> ConstFactoryResult:
         instance = initializer_cls(
             lineno=None,
             col_offset=None,
-            parent=None,
+            parent=SYNTHETIC_ROOT,
             end_lineno=None,
             end_col_offset=None,
         )
@@ -5545,7 +5546,7 @@ def const_factory(value: Any) -> ConstFactoryResult:
         instance = initializer_cls(
             lineno=None,
             col_offset=None,
-            parent=None,
+            parent=SYNTHETIC_ROOT,
             end_lineno=None,
             end_col_offset=None,
         )

Diff for: astroid/nodes/scoped_nodes/__init__.py

@@ -11,6 +11,7 @@
 
 from astroid.nodes.scoped_nodes.mixin import ComprehensionScope, LocalsDictNodeNG
 from astroid.nodes.scoped_nodes.scoped_nodes import (
+    SYNTHETIC_ROOT,
     AsyncFunctionDef,
     ClassDef,
     DictComp,
@@ -37,6 +38,7 @@
     "ListComp",
     "LocalsDictNodeNG",
     "Module",
+    "SYNTHETIC_ROOT",
     "SetComp",
     "builtin_lookup",
     "function_to_method",

Diff for: astroid/nodes/scoped_nodes/scoped_nodes.py

@@ -40,14 +40,7 @@
 from astroid.interpreter.dunder_lookup import lookup
 from astroid.interpreter.objectmodel import ClassModel, FunctionModel, ModuleModel
 from astroid.manager import AstroidManager
-from astroid.nodes import (
-    Arguments,
-    Const,
-    NodeNG,
-    _base_nodes,
-    const_factory,
-    node_classes,
-)
+from astroid.nodes import _base_nodes, node_classes
 from astroid.nodes.scoped_nodes.mixin import ComprehensionScope, LocalsDictNodeNG
 from astroid.nodes.scoped_nodes.utils import builtin_lookup
 from astroid.nodes.utils import Position
@@ -60,6 +53,7 @@
 
 if TYPE_CHECKING:
     from astroid import nodes, objects
+    from astroid.nodes import NodeNG, Const, Arguments
     from astroid.nodes._base_nodes import LookupMixIn
 
 
@@ -353,7 +347,7 @@ def getattr(
         if name in self.special_attributes and not ignore_locals and not name_in_locals:
             result = [self.special_attributes.lookup(name)]
             if name == "__name__":
-                main_const = const_factory("__main__")
+                main_const = node_classes.const_factory("__main__")
                 main_const.parent = AstroidManager().builtins_module
                 result.append(main_const)
         elif not ignore_locals and name_in_locals:
@@ -607,6 +601,14 @@ def _infer(
         yield self
 
 
+class __SyntheticRoot(Module):
+    def __init__(self):
+        super().__init__("__astroid_synthetic", pure_python=False)
+
+
+SYNTHETIC_ROOT = __SyntheticRoot()
+
+
 class GeneratorExp(ComprehensionScope):
     """Class representing an :class:`ast.GeneratorExp` node.
 
@@ -1572,7 +1574,7 @@ def infer_call_result(
             and len(self.args.args) == 1
             and self.args.vararg is not None
         ):
-            if isinstance(caller.args, Arguments):
+            if isinstance(caller.args, node_classes.Arguments):
                 assert caller.args.args is not None
                 metaclass = next(caller.args.args[0].infer(context), None)
             elif isinstance(caller.args, list):
@@ -1583,17 +1585,13 @@ def infer_call_result(
                 )
             if isinstance(metaclass, ClassDef):
                 try:
-                    class_bases = [
-                        # Find the first non-None inferred base value
-                        next(
-                            b
-                            for b in arg.infer(
-                                context=context.clone() if context else context
-                            )
-                            if not (isinstance(b, Const) and b.value is None)
-                        )
-                        for arg in caller.args[1:]
-                    ]
+                    # Find the first non-None inferred base value
+                    get_base = lambda arg: next(
+                        b
+                        for b in arg.infer(context=context.clone() if context else None)
+                        if not (isinstance(b, node_classes.Const) and b.value is None)
+                    )
+                    class_bases = [get_base(arg) for arg in caller.args[1:]]
                 except StopIteration as e:
                     raise InferenceError(node=caller.args[1:], context=context) from e
                 new_class = ClassDef(
@@ -1602,7 +1600,7 @@ def infer_call_result(
                     col_offset=0,
                     end_lineno=0,
                     end_col_offset=0,
-                    parent=AstroidManager().synthetic_root,
+                    parent=SYNTHETIC_ROOT,
                 )
                 new_class.hide = True
                 new_class.postinit(
@@ -2831,7 +2829,7 @@ def _inferred_bases(self, context: InferenceContext | None = None):
                 baseobj = next(
                     b
                     for b in stmt.infer(context=context.clone())
-                    if not (isinstance(b, Const) and b.value is None)
+                    if not (isinstance(b, node_classes.Const) and b.value is None)
                 )
             except (InferenceError, StopIteration):
                 continue

Diff for: 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().synthetic_root,
+            parent=scoped_nodes.SYNTHETIC_ROOT,
             end_col_offset=0,
             end_lineno=0,
         )

Diff for: tests/test_nodes.py

@@ -34,10 +34,8 @@
     AstroidBuildingError,
     AstroidSyntaxError,
     AttributeInferenceError,
-    ParentMissingError,
     StatementMissing,
 )
-from astroid.manager import AstroidManager
 from astroid.nodes.node_classes import (
     AssignAttr,
     AssignName,
@@ -46,7 +44,13 @@
     ImportFrom,
     Tuple,
 )
-from astroid.nodes.scoped_nodes import ClassDef, FunctionDef, GeneratorExp, Module
+from astroid.nodes.scoped_nodes import (
+    SYNTHETIC_ROOT,
+    ClassDef,
+    FunctionDef,
+    GeneratorExp,
+    Module,
+)
 from tests.testdata.python3.recursion_error import LONG_CHAINED_METHOD_CALL
 
 from . import resources
@@ -623,12 +627,10 @@ def _test(self, value: Any) -> None:
         with self.assertRaises(StatementMissing):
             node.statement()
 
-        with self.assertRaises(ParentMissingError):
-            with pytest.warns(DeprecationWarning) as records:
-                node.frame(future=True)
-                assert len(records) == 1
-        with self.assertRaises(ParentMissingError):
-            node.frame()
+        with pytest.warns(DeprecationWarning) as records:
+            assert node.frame(future=True) is SYNTHETIC_ROOT
+            assert len(records) == 1
+        assert node.frame() is SYNTHETIC_ROOT
 
     def test_none(self) -> None:
         self._test(None)
@@ -1962,7 +1964,7 @@ def test_str_repr_no_warnings(node):
             continue
 
         if name == "parent" and "NodeNG" in param_type.annotation:
-            args[name] = AstroidManager().synthetic_root
+            args[name] = SYNTHETIC_ROOT
         elif "int" in param_type.annotation:
             args[name] = random.randint(0, 50)
         elif (