Improve error message when __code__ attribute is not found on annotate function

Author: dr-carlos

Lib/annotationlib.py

@@ -728,7 +728,7 @@ def call_annotate_function(annotate, format, *, owner=None, _is_evaluate=False):
             annotate, owner, is_class, globals, allow_evaluation=False
         )
         func = types.FunctionType(
-            _get_annotate_attr(annotate, "__code__", None),
+            _get_annotate_attr(annotate, "__code__"),
             globals,
             closure=closure,
             argdefs=_get_annotate_attr(annotate, "__defaults__", None),
@@ -763,7 +763,7 @@ def call_annotate_function(annotate, format, *, owner=None, _is_evaluate=False):
         # Grab and store all the annotate function attributes that we might need to access
         # multiple times as variables, as this could be a bit expensive for non-functions.
         annotate_globals = _get_annotate_attr(annotate, "__globals__", {})
-        annotate_code = _get_annotate_attr(annotate, "__code__", None)
+        annotate_code = _get_annotate_attr(annotate, "__code__")
         annotate_defaults = _get_annotate_attr(annotate, "__defaults__", None)
         annotate_kwdefaults = _get_annotate_attr(annotate, "__kwdefaults__", None)
         namespace = {
@@ -890,7 +890,7 @@ def _stringify_single(anno):
         return repr(anno)
 
 
-def _get_annotate_attr(annotate, attr, default):
+def _get_annotate_attr(annotate, attr, default=_sentinel):
     # Try to get the attr on the annotate function. If it doesn't exist, we might
     # need to look in other places on the object. If all of those fail, we can
     # return the default at the end.
@@ -944,6 +944,8 @@ def _get_annotate_attr(annotate, attr, default):
     ):
         return _get_annotate_attr(annotate.func, attr, default)
 
+    if default is _sentinel:
+        raise TypeError(f"annotate function missing {attr!r} attribute")
     return default
 
 def _direct_call_annotate(func, annotate, *args):

Lib/test/test_annotationlib.py

@@ -2119,6 +2119,31 @@ def __call__(self, format, /):
             with self.assertRaises(DemoException):
                 annotationlib.call_annotate_function(Annotate(), format=fmt)
 
+    def test_unsupported_callable_object_fakeglobals_error(self):
+        # Test that a readable error is raised when an unsupported callable
+        # type is used as an annotate function with fake globals.
+
+        def annotate(format, /, __Format=Format,
+                   __NotImplementedError=NotImplementedError):
+            if format == __Format.VALUE:
+                return {"x": int}
+            elif format == __Format.VALUE_WITH_FAKE_GLOBALS:
+                return {"x": str}
+            else:
+                raise __NotImplementedError(format)
+
+        annotations = annotationlib.call_annotate_function(
+            annotate.__call__,
+            Format.VALUE
+        )
+        self.assertEqual(annotations, {"x": int})
+
+        for fmt in (Format.FORWARDREF, Format.STRING):
+            with self.assertRaisesRegex(
+                TypeError, "annotate function missing '__code__' attribute"
+            ):
+                annotationlib.call_annotate_function(annotate.__call__, fmt)
+
 
 class MetaclassTests(unittest.TestCase):
     def test_annotated_meta(self):