How do you do a deprecation warning for a new language being a build dependency? What does it look like? "your build environment is being deprecated"?

In C you can implement a "your build environment is being deprecated" message like this:

    #ifndef I_UNDERSTAND_THAT_SOON_RUST_WILL_BE_MANDATORY
    #error "Starting with version xxx this package will need Rust to compile. Recompile with -DI_UNDERSTAND_THAT_SOON_RUST_WILL_BE_MANDATORY to acknowledge that you understand this warning."
    #endif

Anyone building from source would get notified in a way that's impossible to miss but easy to turn off.

And thousands upon thousands of automated CI jobs and docker container builds fail. You're basically causing massive developer stress to anyone who automatically compiles your package. Most would consider that a bad tradeoff to help a tiny fraction of your users who'd be impacted and also refuse to follow your mailing list.

If the change is transparent to all but a tiny fraction, you can of course guard the above with

    #if !(defined(__AMD64__) || defined(__AARCH64__))

(or whatever the accepted names of those platform macros are).

For whatever it's worth, if the C code in the cryptography package didn't already contain the above check, along with a some hurdle requiring the user to compile with -DNOT_OFFICIALLY_SUPPORTED_TARGET, then the article's point is false: If you don't prevent users from compiling your security-relevant, reliant-on-exact-memory-semantics software on System/390, then you are implicitly supporting System/390.

And for that matter, the Rust code should probably contain a similar check: Even if someone ported Rust to System/390, the cryptography library shouldn't magically start working there, unless the developers actually test there.

> And thousands upon thousands of automated CI jobs and docker container builds fail. You're basically causing massive developer stress to anyone who automatically compiles your package.

This isn’t a major source of stress: you include migration instructions and even tooling to automate it. The thing that’s stressful is when your build fails with completely unexpected errors and no indication of what went wrong.

Loudly announcing breaking changes is disruptive to some extent, but not doing so either means more disruption or nothing can ever change at all.

Isn't this basically equivalent to what they did? Their actual action was to include a dummy rust requirement just to break/warn people who wouldn't be prepared for it as an actual dependency.

You're going to do that a few versions down the line anyway. Why not ahead of time?

The only downstreams this affects more are the ones who decide to suppress the warning for now and ... put it off until you release the change that actually required breakage.

These developers cause themselves stress by building against the latest library without a care in the world. Lock your dependencies, regularly upgrade them while looking at patchnotes, and it won't be a problem.

This is for all intents and purposes exactly what the cryptography maintainers did, except they did one better: they made sure this release is capable of validating the new configuration. They made rust an optional, but on-by-default, dependency. That is the equivalent of #error plus validation. They made it possible to turn this dependency off. That is the equivalent of -DI_UNDERSTAND.

True, that's possible, but quite brutal and I'd expect that would merely have lead to shouting and people going wild over their builds breaking a year earlier.

Yes. It's pretty simple to insert a stub module which is imported in a try/catch, where failure to load results in a warning.

Hm yeah, that sounds like a bit of a hassle to set up (have it build where possible but not fail the build), but otherwise an elegant solution, since it would pass cleanly for people that have a suitable environment.

> project mailing lists, Github issue tracker, project IRC channel, documentation (changelog, FAQ), and Twitter channels

It's hardly a notice posted in a sub-basement 6 months before instituting a breaking change. They communicated via numerous mechanisms.

It's a sub-basement from the perspective of folks for whom this is a second-order dependency. And it sounds like there are many more of them than there are folks that caught wind of this.

Regardless. The common practice is a year of emitting warnings from the software, that the end-user will see. That's prominent and allows package maintainers enough time to work around the upcoming breakage. Six months notice on a mailing list is simply not prominent enough, and it's half the standard year which puts undue strain downstream.