Feature request: graphviz export

[SomeoneSerge]

Hi! I don't know if nix-tree would be an appropriate place for this kind of a "generic" feature, but I think it'd be lovely to be able to do something like this:

❯ nix shell nixpkgs#nix-du nixpkgs#xdot
❯ nix-tree --derivation .#nixosConfigurations.$(hostname).config.system.build.toplevel --graphviz | xdot -i

...and nix-tree already provides the convenient interface of "installables" for the task of enumerating the full closure

Just to give an idea of what output I'm looking for, here's a screenshot for ```console ❯ nix-du -s=500MB | xdot - ``` 

[utdemir]

Thanks for the issue! I agree, this is a useful feature.

If I understand correctly, the difference of your request and:

nix-store -q --graph /nix/store/na56nh4y1m0s1z5rgki99fj7imj433ld-nix-tree-0.3.1

is that, you can pass a flake reference, right?

If so, it does feel like it is more suitable to:

• Either tools like nix-visualize
• Or adding a --graphviz parameter to a flake-aware command like nix store ls or nix path-info.

But on the other hand it really wouldn't be hard to add it to nix-tree, as we have all the dependency graph right there; we just need to print it. I gave it a go on ud/dot branch, can you check it out if it works for you?

nix run 'github:utdemir/nix-tree?ref=ud/dot' -- --derivation .#nixosConfigurations.$(hostname).config.system.build.toplevel --dot | xdot -i

Currently it prints out a simple dot file without any styling, formatting, and it doesn't look very pretty to be honest:

So, I am happy to merge it as-is, or let me know if you have any other suggestions to make it better :).

[SomeoneSerge]

Sorry about disappearing. Yes I think --dot and passing the "flake references" through is good. The graphviz format can be parsed by external tools (e.g. python's networkx), and doesn't seem to include any data other than what nix-tree already deals with. Wouldn't make sense to do more special-casing in nix-tree, and definitely not in the nix repo (nix path-info ... --dot doesn't sound unreasonable, but the nix cli is already overloaded).