Modernize C++ code and improve code quality

[dennisklein]

Summary

Modernize the codebase to use C++20 features and improve overall code quality.

Proposed Changes

High Priority

• Replace custom starts_with() function (main.cpp:34-42) with standard library std::string_view::starts_with() available in C++20

  • Update CMakeLists.txt: target_compile_features(${target} PRIVATE cxx_std_20)
  • Add fallback implementation for older compilers if needed

• Add validation for script path existence and executability in init() function

  • Currently checks s_singularity_script.empty() but default is always set
  • Validate that the script exists and has execute permissions during initialization

• Improve environment variable override logic (main.cpp:417-422)

  • SLURM_SINGULARITY_BIND check only happens if s_bind_mounts.empty()
  • Consider allowing environment variables to consistently override CLI options

Medium Priority

• Rename Buttocks class to SpankWrapper or SpankContext (main.cpp:61)

  • While humorous, a professional name improves maintainability
  • Makes code more accessible to new contributors

• Re-enable and improve input validation for bind paths (main.cpp:269-277)

  • Currently has commented-out space-checking code
  • Add comprehensive validation: invalid characters, path traversal attempts, etc.

• Review static state usage (main.cpp:210-217)

  • Plugin uses inline static variables
  • Document thread-safety guarantees or refactor if needed for concurrent Slurm environments

Benefits

• More maintainable and modern codebase
• Better integration with standard C++ library
• Improved robustness through validation

Compatibility Considerations

• C++20 may not be available on older systems
• Consider maintaining C++17 compatibility with conditional compilation