Infer the actual unpacked value on Dict's getitem() (#1196)

Co-authored-by: Marc Mueller <[email protected]>

Author: isidentical

ChangeLog

@@ -55,6 +55,10 @@ Release date: TBA
 * Fix test for Python ``3.11``. In some instances ``err.__traceback__`` will
   be uninferable now.
 
+* Infer the ``DictUnpack`` value for ``Dict.getitem`` calls.
+
+  Closes #1195
+
 What's New in astroid 2.11.6?
 =============================
 Release date: TBA

astroid/nodes/node_classes.py

@@ -2346,24 +2346,33 @@ def itered(self):
         """
         return [key for (key, _) in self.items]
 
-    def getitem(self, index, context=None):
+    def getitem(
+        self, index: Const | Slice, context: InferenceContext | None = None
+    ) -> NodeNG:
         """Get an item from this node.
 
         :param index: The node to use as a subscript index.
-        :type index: Const or Slice
 
         :raises AstroidTypeError: When the given index cannot be used as a
             subscript index, or if this node is not subscriptable.
         :raises AstroidIndexError: If the given index does not exist in the
             dictionary.
         """
+        # pylint: disable-next=import-outside-toplevel; circular import
+        from astroid.helpers import safe_infer
+
         for key, value in self.items:
             # TODO(cpopa): no support for overriding yet, {1:2, **{1: 3}}.
             if isinstance(key, DictUnpack):
+                inferred_value = safe_infer(value, context)
+                if not isinstance(inferred_value, Dict):
+                    continue
+
                 try:
-                    return value.getitem(index, context)
+                    return inferred_value.getitem(index, context)
                 except (AstroidTypeError, AstroidIndexError):
                     continue
+
             for inferredkey in key.infer(context):
                 if inferredkey is util.Uninferable:
                     continue

tests/unittest_python3.py

@@ -5,7 +5,9 @@
 import unittest
 from textwrap import dedent
 
-from astroid import nodes
+import pytest
+
+from astroid import exceptions, nodes
 from astroid.builder import AstroidBuilder, extract_node
 from astroid.test_utils import require_version
 
@@ -285,6 +287,33 @@ def test_unpacking_in_dict_getitem(self) -> None:
             self.assertIsInstance(value, nodes.Const)
             self.assertEqual(value.value, expected)
 
+    @staticmethod
+    def test_unpacking_in_dict_getitem_with_ref() -> None:
+        node = extract_node(
+            """
+        a = {1: 2}
+        {**a, 2: 3}  #@
+        """
+        )
+        assert isinstance(node, nodes.Dict)
+
+        for key, expected in ((1, 2), (2, 3)):
+            value = node.getitem(nodes.Const(key))
+            assert isinstance(value, nodes.Const)
+            assert value.value == expected
+
+    @staticmethod
+    def test_unpacking_in_dict_getitem_uninferable() -> None:
+        node = extract_node("{**a, 2: 3}")
+        assert isinstance(node, nodes.Dict)
+
+        with pytest.raises(exceptions.AstroidIndexError):
+            node.getitem(nodes.Const(1))
+
+        value = node.getitem(nodes.Const(2))
+        assert isinstance(value, nodes.Const)
+        assert value.value == 3
+
     def test_format_string(self) -> None:
         code = "f'{greetings} {person}'"
         node = extract_node(code)