Cannot pre-build shells with nix-build

[endgame]

I am attempting to pre-build the dependencies of a reflex-platform project (so that my CI doesn't have to rebuild everything on each run). I tried to do this with a

nix-build -A shells.ghc --no-out-link

But the build fails with:

building '/nix/store/xlkmc1g6q1d3ds0q9fdz98nwdf3gm4lp-interactive-work-on-multi--combined-pkg-0-environment.drv'...
unpacking sources
variable $src or $srcs should point to the source
builder for '/nix/store/xlkmc1g6q1d3ds0q9fdz98nwdf3gm4lp-interactive-work-on-multi--combined-pkg-0-environment.drv' failed with exit code 1
error: build of '/nix/store/xlkmc1g6q1d3ds0q9fdz98nwdf3gm4lp-interactive-work-on-multi--combined-pkg-0-environment.drv' failed

I have been able to fudge it with a nix-shell -A shells.ghc --run ':', but it would be better if I could just build it normally.

[endgame]

It turns out that the nix store, after entering both a ghc and a ghcjs shell, becomes so large I cannot make a practical container out of it. I'd like to GC the nix store to try and get it smaller, but the nix-shell "workaround" above doesn't create new GC roots (AFAIK), so if I GC I lose everything. This issue is now more important to me than I first thought; is there anything I can help with to get it moving?

[ryantrinkle]

Perhaps something like this would help - you may have to integrate it upstream into nixpkgs here

[ElvishJerricco]

@ryantrinkle that stuff is going to change a bit here, which actually should make this stuff a lot easier.

[ryantrinkle]

@ElvishJerricco Awesome!

[ali-abrar]

Is there any action that we need to take in reflex-platform to further this along, or is this entirely an upstream issue?

[ali-abrar]

It looks like nix-build -A shells.ghc --no-out-link works in the examples/project folder (added as of #506). Closing based on that, but please reopen if there's more to be done here.