env var to specify path/flake installable/flake-url

[mmlb]

Is your feature request related to a problem?

Not really.

I'd like to put flake.nix and co into a sub-dir of my git repo. This works fine but now I have to explicitly list the subdir when trying to use nix (flake check, develop, build, ...) and I'd rather not, not unlike if I was in a subdir and nix searches up for me already.

Proposed solution

Look into NIX_FLAKE_PATH env var and fall back to fs::current_path(). I have a quick patch that worked for nix flake check and nix flake show. I haven't tried to extend to nix develop or nix build (not sure how it could even work for nix build tbh). And so I thought to ask if there's an appetite for a PR for this.

diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index e2099c401..91919f189 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -54,7 +54,8 @@ public:

     FlakeRef getFlakeRef()
     {
-        return parseFlakeRef(fetchSettings, flakeUrl, fs::current_path().string()); //FIXME
+        auto path = getEnv("NIX_FLAKE_PATH").value_or(fs::current_path().string());
+        return parseFlakeRef(fetchSettings, flakeUrl, path); //FIXME
     }

     LockedFlake lockFlake()

Alternative solutions

Haven't thought of any except continuing with the status quo of using relative path in nix cli invocations.

Additional context

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

---

Add 👍 to issues you find important.