Fallback to type annotations for attribute completions (ipython#15079)

Fixes ipython#14917 

Enable IPython tab completer to use type annotations when attribute
access is restricted by the evaluation policy.

Author: Carreau

IPython/core/guarded_eval.py

@@ -31,7 +31,7 @@
 from IPython.utils.decorators import undoc
 
 
-from typing import Self, LiteralString
+from typing import Self, LiteralString, get_type_hints
 
 if sys.version_info < (3, 12):
     from typing_extensions import TypeAliasType
@@ -1036,6 +1036,22 @@ def dummy_function(*args, **kwargs):
         value = eval_node(node.value, context)
         if policy.can_get_attr(value, node.attr):
             return getattr(value, node.attr)
+        try:
+            cls = (
+                value if isinstance(value, type) else getattr(value, "__class__", None)
+            )
+            if cls is not None:
+                resolved_hints = get_type_hints(
+                    cls,
+                    globalns=(context.globals or {}),
+                    localns=(context.locals or {}),
+                )
+                if node.attr in resolved_hints:
+                    annotated = resolved_hints[node.attr]
+                    return _resolve_annotation(annotated, context)
+        except Exception:
+            # Fall through to the guard rejection
+            pass
         raise GuardRejection(
             "Attribute access (`__getattr__`) for",
             type(value),  # not joined to avoid calling `repr`

tests/test_completer.py

@@ -1572,6 +1572,39 @@ def __getattr__(self, attr):
             self.assertNotIn(".append", matches)
             self.assertNotIn(".keys", matches)
 
+    def test_completion_fallback_to_annotation_for_attribute(self):
+        code = textwrap.dedent(
+            """
+            class StringMethods:
+                def a():
+                    pass
+
+            class Test:
+                str: StringMethods
+                def __init__(self):
+                    self.str = StringMethods()
+                def __getattr__(self, name):
+                    raise AttributeError(f"{name} not found")
+            """
+        )
+
+        repro = types.ModuleType("repro")
+        sys.modules["repro"] = repro
+        exec(code, repro.__dict__)
+
+        ip = get_ipython()
+        ip.user_ns["repro"] = repro
+        exec("r = repro.Test()", ip.user_ns)
+
+        complete = ip.Completer.complete
+        try:
+            with evaluation_policy("limited"), jedi_status(False):
+                _, matches = complete(line_buffer="r.str.")
+                self.assertIn(".a", matches)
+        finally:
+            sys.modules.pop("repro", None)
+            ip.user_ns.pop("r", None)
+
     def test_policy_warnings(self):
         with self.assertWarns(
             UserWarning,