Nix wrote half of my debugger

There is likely a mass of devs that is probably, hmmm, 10x the number of Nix devs from over a year ago, who know exactly what Nix offers and why it is cool, but couldn't be bothered to master it until AI came along and basically "solved the problem".

So I'd expect AI to rapidly accelerate Nix adoption. Hopefully, because it is amazing.

"What is this superpower, and why is nobody else using it?"

The "Undo" time-travelling debugger for C/C++ has been around for 20+ years. So I guess the answer is simply that most people chase shiny new things instead of using established, reliable, and, hence, boring tools.

Seeing Nix these days is such a whiplash experience. We have fully deterministic systems and then we have LLMs. God ;)

I kind of confused what nix has to do with this considering it seems to basically be reimplementing rr?

I'd love to become a Nix user one day. I tried to write a rather complex flake one day; it ended up with Nix (nix command) deleting itself: I immediately lost trust with it.

I find myself moving more and more non-build things into nix builds because I don't want to roll my own cache invalidation. Seems like this is yet another reason to do so.

Dude, this is amazing stuff. Farid really is putting out banger after Nix banger haha. This sounds like a mini/less capable Antithesis runtime, but running on your machine.

Curious: how does Rewind deal with randomness?

The following page explains how Rewind VM works:

https://rewindvm.dev/#how

...of which the following are most important:

2. Run deterministically

One vCPU on stock KVM, so code in the VM runs on the real CPU. The VM's kernel carries a small Rewind platform: interrupts arrive only when the VM hands control to Rewind, time moves only then, and the timestamp counter and hardware RNG are hidden. A step is one of those handoffs.

3. Keep keyframes

Every quarter second of wall time, Rewind snapshots the machine using KVM's dirty-page [aka Memory Pages that have been written to since the last snapshot] log. Pages go into a content-addressed store (BLAKE3, zstd), so a page shared by keyframes, runs and forks is stored once."

Now, that's some brilliant engineering right there!

While I like the product name "Rewind VM" (and yes, that's what it allows the user to do!), it could just as easily be called "Deterministic VM" and that name would have been wholly appropriate, as well!

Future OS and VM engineers should study Rewind VM. Those are some great engineering ideas there, and determinism, or at least optional determinism, should it be desired, when it is desired -- is the one thing that is completely non-existent in most OS's, most VM's, and most other program runtime environments...

Anyway, a great article on using Rewind VM (never knew about it before this article!) with Nix builds.

[flagged]

[flagged]

[flagged]

[flagged]

[flagged]