Split off a nix-store-pure

[Ericson2314]

Motivation

• The nix-store library is too big!
• Having a WASM/enscripten build would be very nice. That build cannot have e.g. LocalStore anyways.
  • https://nixcloud.io/tour is a cool thing made from an ancient enscripten build of Nix. I would like for it to be more official, and easy to update to new versions of Nix.
• We could have a CPP soup to disable things for the WASM build, but that is hard to maintain. A library split is better because then people doing regular builds won't regress the intended separation.

Method

We could either split of a nix-store-pure or a nix-store-io --- in essence this is asking which of the two resulting libraries should inherit the nix-store name, and which should have to get a new name. For compat, making nix-store the downstream library which has the same interface is better.

• nix-expr should only depend on nix-store-pure
• We may also need a nix-util-pure

[Ericson2314]

CC

• @qknight for making https://nixcloud.io/tour
• @tomberek for also being involved in the enscripten build
• @puffnfresh because I think this is also an opportunity for making sure we get the SourceAccess and CanonPath usage right.
  • We have the option of simulating a single-root Unix-style file system or a multi-root Windows-style files system in the browser :)

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-01-15-nix-team-meeting-minutes-208/58993/1

[tomberek]

Another really dirty example of an emscripten build: https://github.com/flox/nix/tree/wasm

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-01-22-nix-team-meeting-minutes-210/59239/1