I don't think that's right - even if you had the full source code for either of those, it's extremely unlikely you'd be able to build them on your own machine.

Building them would be a challenge, but definitely not an insurmountable one. I’ve worked on a couple of C++ projects at a similar scale to Windows (millions of LOC) and the build systems were a major pain. But a determined engineer with the readme file and no other help could get it building in a week or so.

(This probably says more about how hard it is to build C++ than anything else)

Some years ago someone that worked at Microsoft told me he didn't think any individual engineer who already works on Windows could ever get Windows building by themselves with just the code.

That just shows their bias. If the code is complete, it's only a matter of time to figure out how to build it.

May not take hours, but determined engineer should be able to figure it out.

I think you're being naive. Microsoft has spent 1000s of engineering years on their build system. You aren't going to just replicate that in a week.

As a user said below, you wouldn't need cross platform support, incremental builds, tests to run, etc.

Just getting the code to compile, link, baking in assets, etc. For a single architecture is a much more reasonable goal.

I'd imagine it'd be on the scale of 1-3months for an engineer to get working full time, but large error bars around this figure

Plus it already has been done before with Windows XP, without even any documentation and there is a guide on the internet on how to build Windows Server 2003.

This was done (if I remember right) when governments and big customers had access to the Windows source-code.

You’re also not trying to get a full CICD pipeline complete with unit/integration tests, crypto signatures, ability to flip features on and off with a click , monitoring of the cicd pipeline, scaled so 1000s of engineers can work at once etc

Microsoft uses Azure DevOps for products as large as Visual Studio.

> But a determined engineer with the readme file and no other help could get it building in a week or so.

That's probably true, but I wouldn't be surprised if something like windows doesn't have a README file. And it does have build instructions they may well be in some wiki separated from the source code.

Fwiw C++ is hard to build specifically, but any large project with assets is a challenge to build.

Video games build systems are a thing onto themselves even taking the c++ issues out of the equation.

Hell even comparatively simole microservices in modern CRUD apps have resorted to docker to do away with pains of rebuilding stuff.

I don't really think it is a language ting, just more of a project size thing.

Well, it kind of is a language thing. Many newer languages (Rust and Go come to mind) are much more consistent in the way you interact with them as your project scales.

there's 99% complete leaked windows xp source code that people have managed to compile

There are even nice timelapse videos of that process: https://vimeo.com/464644850 (you’ll need a Vimeo account to see it, because Vimeo is weird like that. This was on YouTube originally, but it was taken down.)

I think the comparison is windows ISO image, not the source code. Code used to train LLAMA is open source, but it still requires money to use that.

More like a compiled version of Windows.