Rustytwin

[Overcomplicated12]

RustyTwin: Differential Migration Test Runner

Introduces RustyTwin, a standalone Rust CLI for checking behavioral equivalence between baseline C++ code and RustyCpp/inline-Rust DSL migrations.

RustyTwin is intentionally scoped to focused, deterministic module behavior. It does not build Mako, inspect ABI, parse Clang ASTs, generate fuzz inputs, shrink failures, or run full Raft clusters.

What It Does

RustyTwin runs the same NDJSON operation tape against a baseline and candidate executable, then compares their observable behavior.

It captures:

• Ordered NDJSON events
• Standard output and standard error
• Exit status and signals
• Per-harness timeouts
• First behavioral divergence
• Self-contained replay artifacts for failed checks

The comparator preserves event order, compares JSON structurally, normalizes trailing stdout whitespace, and ignores elapsed-time-style metadata.

Commands

Generic Harness Check

rustytwin check \
  --baseline-bin /path/to/baseline-harness \
  --candidate-bin /path/to/candidate-harness \
  --tape /path/to/operations.ndjson \
  --out /tmp/rustytwin-results \
  --timeout-ms 5000