nix: Fix submodules

[cleverca22]

this PR switches the flakes from using submodules manually (which can also break due to NixOS/nix#13698 )
over to using submodules via flakes (which then also needs nix to be upgraded)

this is required, because fetching the project via a flake URI such as nix build github:grumpycoders/pcsx-redux/1b0cbe5e4a535def2e3e3279551e6665cdc102ae completely breaks the build
which also makes it impossible to add this project as an input on another flake

[coderabbitai]

Walkthrough

The change updates the pcsx-redux.nix build script to use the cp -ruT command instead of cp -ru when copying submodules and dependencies into the third_party directory. It also removes a commented-out line for NIX_BUILD_CORES and cleans up a trailing blank line.

Changes

Cohort / File(s)	Change Summary
Nix build script adjustments pcsx-redux.nix	Updated cp command flags from -ru to -ruT for submodule and dependency copying; removed a commented-out NIX_BUILD_CORES line and cleaned up a trailing blank line.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• Nix: Add OpenBIOS to the build and refactor derivation #1923: Introduced the fetchSubmodule function and restructured submodule handling, which is directly adjusted by this PR.

Poem

A rabbit hops through Nix with glee,
Tweaking flags for cp with care and esprit.
No more stray comments or trailing space,
The build script's tidy, in its rightful place.
With -ruT in paw, I bound ahead—
Clean code and carrots, both well-fed! 🥕

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• pcsx-redux.nix (2 hunks)

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• pcsx-redux.nix

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[cleverca22]

ah crud!

git+https://github.com/cleverca22/pcsx-redux?ref=fix-submodules fetches the repo successfully, but silently ignores submodules
github:cleverca22/pcsx-redux/fix-submodules poisons the lock file, error: input attribute 'submodules' not supported by scheme 'github' and then you cant do anything to fix it, until you manually revert flake.lock

i'll need to revert the submodule improvements, and go for the backup fix

[nicolasnoble]

@NotExactlySiev ping

[NotExactlySiev]

Your solution works perfectly (thanks!) and could be merged in right now. However: those cp commands were meant to be only a temporary solution until I figure out a better way to do it. The correct solution imo would be to stop having those dependencies' paths be hardcoded to the third_party directory and instead modify the Makefile to receive their paths from an environment variable set by the derivation. This way the build can access these dependencies directly from the store without needing to copy anything. We already did something a bit like this in the Makefile for the luajit deps.

Also: I added NIX_BUILD_CORES = 4 because trying to build redux on my (16GB RAM + 16GB Swap) laptop causes the entire PC to hang for a few minutes before the build process crashes :P But I'm fine with removing it as I don't want other people who unlike me don't have limited RAM be forced into slow builds. Ideally there could be a check inside the derivation for the amount of available RAM before setting that variable, but I don't know how something like that will ever work within Nix's purity limits.
For now we can have it be unlimited by default and I'll just override it on my local system. But I expect a few other users to eventually run into the same problem and be confused as to why attempting to install pcsx-redux hangs their nix system 😛 So that's something we might have to think about.

[cleverca22]

Also: I added NIX_BUILD_CORES = 4 because trying to build redux on my (16GB RAM + 16GB Swap) laptop

that should really be set in nix.conf
the way it is currently, it actively ignores my config, and i have to change the source to build with a different count
and because of the nix fetching bug, any change of the source fixed the problem, making it very hard to tell if it was a concurrency bug, due to it always using 4 threads

but yeah, nix itself doesnt have a good way to balance many small processes vs a few fat ones

[NotExactlySiev]

that should really be set in nix.conf
ah that makes sense. wouldn't help in this case, as I usually have no issue building with 16 threads. it's just that compiling redux uses an unusually large amount of RAM per process due to heavy template use. still, manually overriding it for this one specific package works fine for me.
also due to the nature of the bug it was evading detection in the CI/CD checks so good catch!

[nicolasnoble]

Note that I'm vendoring and pinning dependencies for a reason. Trying to use system packages where things are pinned and vendored is a bad idea. You break it, you buy it.

[NotExactlySiev]

We're still mostly using the vendored dependencies. it's just that nix likes to download them to /nix/store/<some random string> which then has to be copied into third_party. it would be nice if the build was able to address them where they're downloaded so we can avoid the copying.