Limit arbitrary captures

func_adl/util_ast.py

@@ -337,6 +337,13 @@ def visit_Name(self, node: ast.Name) -> Any:
                 # Modules should be sent on down to be dealt with by the
                 # backend.
                 if not isinstance(v, ModuleType):
+                    legal_capture_types = [str, int, float, bool, complex, str, bytes]
+                    if type(v) not in legal_capture_types:
+                        raise ValueError(
+                            f"Do not know how to capture data type '{type(v).__name__}' for "
+                            f"variable '{node.id}' - only {', '.join([c.__name__ for c in legal_capture_types])} are "
+                            "supported."
+                        )
                     return as_literal(v)
         return node
 

tests/test_util_ast.py

@@ -309,6 +309,19 @@ def test_parse_lambda_capture_nested_local():
     assert ast.dump(r) == ast.dump(r_true)
 
 
+def test_sensible_error_with_bad_variable_capture():
+    class bogus:
+        def __init__(self):
+            self.my_var = 10
+
+    my_var = bogus()
+
+    with pytest.raises(ValueError) as e:
+        parse_as_ast(lambda x: x > my_var)
+
+    assert "my_var" in str(e)
+
+
 def test_parse_simple_func():
     "A oneline function defined at local scope"