Docker image broken

[srid]

https://github.com/srid/notes.srid.ca/runs/2347514181?check_suite_focus=true

docker: Error response from daemon: OCI runtime create failed: container_linux.go:367: starting container process caused: exec: "neuron": executable file not found in $PATH: unknown.
time="2021-04-14T21:59:22Z" level=error msg="error waiting for container: context canceled"

Looks to be regression from #594

[TheKK]

May I ask you why the regression happens? It's a little beyond my understanding with nix.

AFAIK,
import ./. in docker.nix > default.nix > defaultPackage in flake.nix > (import ./project.nix { inherit pkgs; }).neuron

should be identical to
(import ./project.nix {}).neuron

Do you think this is an flake-compat issue? Or anything subtle I missed.

[srid]

@TheKK see https://nixos.wiki/wiki/Import_From_Derivation

They are not identical. The former (when importing default.nix) requires a callPackage, but with project.nix, importing alone gets you neuron derivation. Both approaches will work, but I went with the latter because then there is no need to import nixpkgs.nix again (when invoking callPackage).

It is nothing to do with flake per se.

[TheKK]

Oh, I just found that it might not be the issue of IFD. Some simple experiment correct my wrong expectation.

flake-compat actually returns the entire flake plus the default attribute, which is a derivation points to our defaultPackage.

repl> import ./.
{ apps = { ... };
 default = «derivation /nix/store/k9ljivccyvn4bm624w1g3mazpx65pw0q-neuron-1.9.27.2.drv»;
 defaultApp = { ... };
 defaultPackage = { ... };
 devShell = { ... }; 
 inputs = { ... };
 lastModified = 1618440730;
 lastModifiedDate = "20210414225210";
 narHash = "sha256-Q6ukNOOxd3m++WGbR5FmGkwcoTu0kS/NsQuMDcsL72s=";
 outPath = "/nix/store/smqsgc1wm1rzrzcm2x6gwq2bx3l11rm8-source";
 outputs = { ... };
 packages = { ... };
 rev = "54975f803cae925dc2d6aa29de92aab875cef16c";
 revCount = 1604; shortRev = "54975f8"; sourceInfo = { ... }; submodules = false; }

So import ./. is different from (import ./project.nix { inherit pkgs; }).neuron obviously. The next question comes to me is why nix-build still works on this default.nix? Then I found that nix-build accepts derivation and an object that some of its values are derivation. And our default field from default.nix got built by nix-build magically!

[srid]

Interesting. Is that nix-build behaviour (of accepting .default attr) documented somewhere? I wonder if that's a Nix 2.4 only behaviour.

[TheKK]

From the doc of Nix 2.3.10

nix-build is essentially a wrapper around nix-instantiate (to translate a high-level Nix expression to a low-level store derivation) and nix-store --realise (to build the store derivation).

The command nix-instantiate generates store derivations from (high-level) Nix expressions. It evaluates the Nix expressions in each of files (which defaults to ./default.nix). Each top-level expression should evaluate to a derivation, a list of derivations, or a set of derivations.

I can't find the old document but looks like it's not recent added feature.