This is not ca-derivations. We don't care about self-references or any of the
rewriting or stuff like that; if you want something like that, write
your user code so it figures out where it is.
The reason I want to do this is for integrating other build systems with
Lix: if you're importing something built *outside the store* with a
non-Nix build system, it makes no sense to put it in an input-addressed
path since it's not possible to come up with a derivation for it.
But you need *some* hash, so the output hashing is the most sensible option.
It is also nice because of not needing trusted user privileges to import
it, since the hash describes the exact contents of the output path.
We use this feature (implemented externally to Lix; this CL eliminates
that step) at Mercury to integrate buck2 with Nix on the output side: we
import things to the Nix store as ca paths with references.
These can then be consumed by Nix language with:
```
# Hack from https://git.lix.systems/lix-project/lix/issues/402#issuecomment-5889
path:
builtins.appendContext path {
${path} = {
path = true;
};
}
```
Test plan:
```
$ nix store add-path --references-list xx-refs-list ./README.md
/nix/store/szcwnm13d9gmxx8fly0bz82l42jgysw6-README.md
$ cat xx-refs-list
/nix/store/g9hhwjbkdrw0wnbd3axfs4icyb37nr6b-bash-interactive-5.3p3
$ nix path-info --json /nix/store/szcwnm13d9gmxx8fly0bz82l42jgysw6-README.md | jq .
[
{
"ca": "fixed:r:sha256:1pj59fy7zcrn949ry9kgv4ba17h2sy3z2is469abj912cvbl14n3",
"narHash": "sha256-w5JA12YiJLlUMkRH8YfXAp6gFtlvJp8TSTazf7xLRd4=",
"narSize": 1384,
"path": "/nix/store/szcwnm13d9gmxx8fly0bz82l42jgysw6-README.md",
"references": [
"/nix/store/g9hhwjbkdrw0wnbd3axfs4icyb37nr6b-bash-interactive-5.3p3"
],
"registrationTime": 1771266146,
"valid": true
}
]
```
Change-Id: I005a03003dfc24108e018e599dbe0b5d6a6a6964
Jade Lovelace
01ff67595b