How to get image tag from dockerTools build{Layered}Image?

Help
1

I can use dockerTools buildImage or buildLayeredImage to build an image, and then import it to docker (docker load) or send it to a registry. But if I let nix generate the image tag automatically (from inputs I assume), I can’t access it. I’ve seen workarounds that parse the output from docker load (which prints the image name including tag to stdout), but that seems as that, a workaround.

Would it be possible to make the tag available in the return value of buildImage/buildLayeredImage? Eg. something like

let
  image = dockerTools.buildLayeredImage { … }

  tag = image.tag // <- the tag as generated by nix.
2

Isn’t the tag already available under the imageTag attribute?

$ nix eval nixpkgs#dockerTools.examples.bashNoTagLayered.imageTag
"0k0pyqixv5s32gzsr5pjg3pmgas9kbjf"
3

Indeed, imageTag is it.

For future, where would one find documentation about what attributes exist on the object that buildLayeredImage returns?

4

I’m not aware of any such documentation sadly.

5

While the documentation is infamously lacking, you can use tab completion in the nix repl to explore at least. I also find just reading the nixpkgs source is surprisingly useful, though it’s annoying I have to so frequently.