Module codegen_version 

RFC-0090 / phase-429 — the codegen version, the one token that says whether generated code and this runtime can work together.

What breaks without it

nano-ros shipped prebuilt nros binaries early and stopped, because a released binary emitted code that had drifted from the runtime. The failure is not loud: drifted generated code compiles, and the image is simply wrong in whatever way the generator was wrong. Issue 1018 records the canonical instance — the C emitter transposed sequence-of-strings dimensions in all three emission sites (char data[256][64] for [64][256]) — caught by a developer’s build refusal, which is a thing no user has.

The relation that breaks is generated code ↔ runtime. The binary is only the thing that produced one side of it, which is why the version lives here, in the runtime, rather than in the CLI.

Why an integer and not a hash

A hash cannot say WHICH SIDE IS BEHIND, and that distinction is the whole value of the token: G < MIN is “regenerate, silently” and G > VERSION is “a human must move a pin”. They are not interchangeable remedies. A hash also moves when a doc comment moves, and a check that fires on cosmetic change is one people learn to bypass — NROS_SKIP_VERSION_CHECK is right there.

Not to be confused with the codegen FINGERPRINT

nros codegen-fingerprint hashes every byte the emitters produce for a compiled-in corpus. It answers “would this binary emit different bytes?” — a FRESHNESS question, whose remedy is to regenerate, silently. The constants here answer “can this code work with this runtime?” — a COMPATIBILITY question, whose remedy is a refusal. Conflating them is why issue 1018’s stale-CLI refusal both over-fires on cmd/doctor.rs and cannot ship.

The module’s own file carries no //! docs deliberately; see the comment at its head.

Where the negative case is proven

just check codegen-version-refusal builds artifacts carrying an out-of-range version and requires each language to refuse: #error for C and C++, error[E0080] for Rust. A check that has never been observed to fail is a check nobody has evidence still works, and this one guards a failure whose whole character is that it is silent.

Constants

NROS_CODEGEN_VERSION

The codegen version this runtime emits and accepts.

NROS_CODEGEN_VERSION_MIN

The oldest codegen version this runtime still accepts.

Functions

accepts

Does emitted fall in the range this runtime accepts?