Add support for binary union types - Python 3.10 (#1977)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

3 files changed, 84 insertions, 2 deletions

diff --git a/astroid/bases.py b/astroid/bases.py
index d6c830c7..e930328e 100644
--- a/astroid/bases.py
+++ b/astroid/bases.py
@@ -121,11 +121,12 @@ class Proxy:
         if proxied is None:
             # This is a hack to allow calling this __init__ during bootstrapping of
             # builtin classes and their docstrings.
-            # For Const and Generator nodes the _proxied attribute is set during bootstrapping
+            # For Const, Generator, and UnionType nodes the _proxied attribute
+            # is set during bootstrapping
             # as we first need to build the ClassDef that they can proxy.
             # Thus, if proxied is None self should be a Const or Generator
             # as that is the only way _proxied will be correctly set as a ClassDef.
-            assert isinstance(self, (nodes.Const, Generator))
+            assert isinstance(self, (nodes.Const, Generator, UnionType))
         else:
             self._proxied = proxied
 
@@ -669,3 +670,41 @@ class AsyncGenerator(Generator):
 
     def __str__(self) -> str:
         return f"AsyncGenerator({self._proxied.name})"
+
+
+class UnionType(BaseInstance):
+    """Special node representing new style typing unions.
+
+    Proxied class is set once for all in raw_building.
+    """
+
+    _proxied: nodes.ClassDef
+
+    def __init__(
+        self,
+        left: UnionType | nodes.ClassDef | nodes.Const,
+        right: UnionType | nodes.ClassDef | nodes.Const,
+        parent: nodes.NodeNG | None = None,
+    ) -> None:
+        super().__init__()
+        self.parent = parent
+        self.left = left
+        self.right = right
+
+    def callable(self) -> Literal[False]:
+        return False
+
+    def bool_value(self, context: InferenceContext | None = None) -> Literal[True]:
+        return True
+
+    def pytype(self) -> Literal["types.UnionType"]:
+        return "types.UnionType"
+
+    def display_type(self) -> str:
+        return "UnionType"
+
+    def __repr__(self) -> str:
+        return f"<UnionType({self._proxied.name}) l.{self.lineno} at 0x{id(self)}>"
+
+    def __str__(self) -> str:
+        return f"UnionType({self._proxied.name})"
diff --git a/astroid/inference.py b/astroid/inference.py
index 59bc4eca..8ec191a4 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -15,6 +15,7 @@ from collections.abc import Callable, Generator, Iterable, Iterator
 from typing import TYPE_CHECKING, Any, Optional, TypeVar, Union
 
 from astroid import bases, constraint, decorators, helpers, nodes, protocols, util
+from astroid.const import PY310_PLUS
 from astroid.context import (
     CallContext,
     InferenceContext,
@@ -758,6 +759,14 @@ def _bin_op(
     )
 
 
+def _bin_op_or_union_type(
+    left: bases.UnionType | nodes.ClassDef | nodes.Const,
+    right: bases.UnionType | nodes.ClassDef | nodes.Const,
+) -> Generator[InferenceResult, None, None]:
+    """Create a new UnionType instance for binary or, e.g. int | str."""
+    yield bases.UnionType(left, right)
+
+
 def _get_binop_contexts(context, left, right):
     """Get contexts for binary operations.
 
@@ -817,6 +826,22 @@ def _get_binop_flow(
             _bin_op(left, binary_opnode, op, right, context),
             _bin_op(right, binary_opnode, op, left, reverse_context, reverse=True),
         ]
+
+    if (
+        PY310_PLUS
+        and op == "|"
+        and (
+            isinstance(left, (bases.UnionType, nodes.ClassDef))
+            or isinstance(left, nodes.Const)
+            and left.value is None
+        )
+        and (
+            isinstance(right, (bases.UnionType, nodes.ClassDef))
+            or isinstance(right, nodes.Const)
+            and right.value is None
+        )
+    ):
+        methods.extend([functools.partial(_bin_op_or_union_type, left, right)])
     return methods
 
 
diff --git a/astroid/raw_building.py b/astroid/raw_building.py
index 8575f41e..453ce8b2 100644
--- a/astroid/raw_building.py
+++ b/astroid/raw_building.py
@@ -575,6 +575,24 @@ def _astroid_bootstrapping() -> None:
         )
         bases.AsyncGenerator._proxied = _AsyncGeneratorType
         builder.object_build(bases.AsyncGenerator._proxied, types.AsyncGeneratorType)
+
+    if hasattr(types, "UnionType"):
+        _UnionTypeType = nodes.ClassDef(types.UnionType.__name__)
+        _UnionTypeType.parent = astroid_builtin
+        union_type_doc_node = (
+            nodes.Const(value=types.UnionType.__doc__)
+            if types.UnionType.__doc__
+            else None
+        )
+        _UnionTypeType.postinit(
+            bases=[],
+            body=[],
+            decorators=None,
+            doc_node=union_type_doc_node,
+        )
+        bases.UnionType._proxied = _UnionTypeType
+        builder.object_build(bases.UnionType._proxied, types.UnionType)
+
     builtin_types = (
         types.GetSetDescriptorType,
         types.GeneratorType,