Detect local arguments and functions used in a function

[Copilot]

Summary

Adds AST-based undefined-variable detection to dependency_parser so that external symbols used by a function can be identified and resolved for dependency tracking. Local (nested) function definitions are explicitly forbidden—raising NotImplementedError early—to avoid silent mis-resolution rather than producing incorrect dependency graphs.

Related Issue(s)

Follow-up to #155.

Backward Compatibility

Functions containing nested def or async def blocks will now raise NotImplementedError when passed to find_undefined_variables or get_call_dependencies. Previously these were silently (and incorrectly) processed.

Implementation Notes

• UndefinedVariableVisitor — rewrites the AST visitor with a _nesting_depth counter. Any FunctionDef/AsyncFunctionDef encountered at depth > 0 raises NotImplementedError with a message that distinguishes def from ``async def`:

  NotImplementedError: Local function definitions are not supported:
  'def helper' inside a function body cannot be analysed for dependencies.
  

• Argument coverage — registers all argument kinds (posonlyargs, args, kwonlyargs, *args, **kwargs) in defined_vars, eliminating false positives from these names.
• get_call_dependencies — resolves each undefined symbol via object_scope and recursively collects unversioned objects.
• Tests added:
  • test_local_function_definition_raises / test_local_async_function_definition_raises — verify the new early-failure behavior.
  • test_all_argument_kinds_are_defined — guards against regression on argument-kind coverage.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.65%. Comparing base (2d48634) to head (dbb1188).
⚠️ Report is 3 commits behind head on args.

Additional details and impacted files

@@            Coverage Diff             @@
##             args     #190      +/-   ##
==========================================
+ Coverage   97.47%   97.65%   +0.18%     
==========================================
  Files          34       34              
  Lines        2295     2305      +10     
==========================================
+ Hits         2237     2251      +14     
+ Misses         58       54       -4     

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