Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Fix AST visitor traversal order (#5221)
## Summary According to the AST visitor documentation, the AST visitor "visits all nodes in the AST recursively in evaluation-order". However, the current traversal fails to meet this specification in a few places. ### Function traversal ```python order = [] @(order.append("decorator") or (lambda x: x)) def f( posonly: order.append("posonly annotation") = order.append("posonly default"), /, arg: order.append("arg annotation") = order.append("arg default"), *args: order.append("vararg annotation"), kwarg: order.append("kwarg annotation") = order.append("kwarg default"), **kwargs: order.append("kwarg annotation") ) -> order.append("return annotation"): pass print(order) ``` Executing the above snippet using CPython 3.10.6 prints the following result (formatted for readability): ```python [ 'decorator', 'posonly default', 'arg default', 'kwarg default', 'arg annotation', 'posonly annotation', 'vararg annotation', 'kwarg annotation', 'kwarg annotation', 'return annotation', ] ``` Here we can see that decorators are evaluated first, followed by argument defaults, and annotations are last. The current traversal of a function's AST does not align with this order. ### Annotated assignment traversal ```python order = [] x: order.append("annotation") = order.append("expression") print(order) ``` Executing the above snippet using CPython 3.10.6 prints the following result: ```python ['expression', 'annotation'] ``` Here we can see that an annotated assignments annotation gets evaluated after the assignment's expression. The current traversal of an annotated assignment's AST does not align with this order. ## Why? I'm slowly working on #3946 and porting over some of the logic and tests from ssort. ssort is very sensitive to AST traversal order, so ensuring the utmost correctness here is important. ## Test Plan There doesn't seem to be existing tests for the AST visitor, so I didn't bother adding tests for these very subtle changes. However, this behavior will be captured in the tests for the PR which addresses #3946.
- Loading branch information