zopefoundation / RestrictedPython / 36334361621

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Pull #332

github

feat: deny every ast node explicitly with a documented reason

"Explicit is better than implicit." (PEP 20)

Every ast node of the supported Python versions now has an explicit
visit_<node> method in RestrictingNodeTransformer. generic_visit stays
the safety net for nodes of new Python versions nobody has reviewed yet;
it is no longer the place where the decision about a known language
feature is recorded.

- Deny explicitly the nodes which were only denied by generic_visit:
  AnnAssign, Match with all pattern nodes and match_case, TypeAlias,
  TypeVar, ParamSpec, TypeVarTuple, FunctionType and TypeIgnore.
- Explain in the docstring of every denying method why the node is
  denied and which guard or check it would bypass; also for the
  existing ones (Nonlocal, TryStar, async).
- Add tests which allow the pattern nodes and show the bypasses:
  class, mapping and sequence patterns access the subject without
  _getattr_, _getitem_ and _getiter_; capture names escape the check
  for a leading underscore.
- Add a test which fails for every ast node of the running Python
  without a visit_<node> method.
- Replace the open "Option 1 / Option 2" todo in the contributing
  documentation by the rule.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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