Porting Python's natsort to Rust revealed that verification, not coding, is the hard part

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A developer ported Python's natsort library to Rust for Port Mortem 2026, finding that writing the sorting algorithm was straightforward but rigorously verifying identical behavior across thousands of edge cases was the true challenge. The verification pipeline combined the original Python test suite, differential fuzzing, property testing, and mutation testing to compare outputs between both implementations. During fuzzing, the port uncovered a genuine bug in the mature natsort library itself, where numbers overflowing to floating-point infinity produced inconsistent sort orders depending on input sequence, which was subsequently reported upstream. A silent fallback to an incorrect Python adapter and five separate Windows-specific bugs — including encoding mismatches and missing executable extensions — further demonstrated that testing on a single platform is insufficient. The project concluded that achieving a compiling, seemingly correct port represents only a small fraction of the real work, with systematic, cross-platform verification making up the rest.

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