Update function parsing to handle externalptr and add unlistable fallback

[jayqi]

Make .parse_function more robust and fix error from externalptr.

• Refactor listable check into .is_listable_expr and add check for externalptr type
• Refactor as.list(x) into .try_as_list with fallback and logging a warning

Closes #343

TODO:

• Test on FIMS
• Add unit tests

[Copilot]

Pull request overview

This pull request addresses issue #343 where FunctionReporter would fail with an error when analyzing packages that use Rcpp, due to the presence of externalptr type expressions that cannot be converted to lists. The fix makes expression parsing more robust by:

1. Extracting the "listable" check into a dedicated .is_listable_expr() function that explicitly handles external pointers
2. Creating a .try_as_list() wrapper that gracefully handles as.list() failures with logging
3. Updating both .parse_function() and .parse_R6_expression() to use these new utilities

Changes:

• Refactored listable expression checking into .is_listable_expr() with explicit handling for externalptr types
• Added .try_as_list() function with error handling and fallback behavior
• Updated .parse_function() and .parse_R6_expression() to use the new helper functions
• Added comprehensive unit tests for the new behavior
• Updated NEWS.md with bugfix entry

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
R/FunctionReporter.R	Added .is_listable_expr() and .try_as_list() helper functions; refactored .parse_function() and .parse_R6_expression() to use these helpers for robust expression parsing
tests/testthat/test-FunctionReporter-class.R	Added tests for external pointer handling and fallback behavior when as.list() fails
NEWS.md	Added bugfix entry documenting the fix for externalptr runtime error

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[jameslamb]

Thanks, yep I support this approach.

If you found that this is doing what you want on #343, I'm good with it.

[bburns632]

LGTM

[kellijohnson-NOAA]

Brilliant and so fast 🚀 . Thank you!