Add reference to vic/with-inputs

[vic]

with-inputs is related (alternative to nix flakes) in the sense that it allows flake-like inputs for projects using npins or other non-flake locking mechanism.

[aanderse]

hi @vic 👋

i'm trying to play around with with-inputs and lon - i think i am missing something obvious...

❯ nix repl
Nix 2.31.3
Type :? for help.
nix-repl> sources = import ./lon.nix

nix-repl> sources
{
  ndg = "/nix/store/l115h1xyaacyaac0j08id7srd2wwpjl1-source";
  nixpkgs = "/nix/store/s08d9f5avsqs69r1y2gyivxgfwv4a88c-source";
}

nix-repl> with-inputs = import ./with-inputs.nix sources { }

nix-repl> outputs = inputs: { }

nix-repl> (with-inputs outputs).inputs
{
  __functor = «lambda __functor @ /home/aaron/nix/framework/with-inputs.nix:136:5»;
  ndg = «error: expected a set but found a string with context: "/nix/store/l115h1xyaacyaac0j08id7srd2wwpjl1-source"»;
  nixpkgs = «error: expected a set but found a string with context: "/nix/store/s08d9f5avsqs69r1y2gyivxgfwv4a88c-source"»;
  self = { ... };
}

any advice you can provide would be greatly appreciated 🙇‍♂️

[vic]

Hey, @aanderse. I did not know of Lon, thanks for pointing to it.

From your code, looks like sources is an attrset of string paths. with-inputs expects values to have outPath at least. (like those sources from npins), so perhaps the following can help:

sources = mapAttrs (_: outPath: { inherit outPath; }) (import ./lon.nix);

I will also try to add another example at with-inputs using lon, we currently have examples for npins, unflake, and nixlock.

[aanderse]

ah, outPath was the missing piece, thank you

any idea on this one?

here are the details of the flake i am importing:

    "ndg": {
      "type": "GitHub",
      "fetchType": "tarball",
      "owner": "feel-co",
      "repo": "ndg",
      "branch": "main",
      "revision": "0c898318cdb7b8288a58f6393b1d8ba0dd6b0a09",
      "url": "https://github.com/feel-co/ndg/archive/0c898318cdb7b8288a58f6393b1d8ba0dd6b0a09.tar.gz",
      "hash": "sha256-BedBcz5+dDHhNWMY4JndabYUMSOMusKzFGLV1PxvwBQ="
    }

[vic]

Yep, with-inputs takes the following args:

with-inputs sources follows outputsFn

Try using:

with-inputs sources { } lib.id

that would be like outputs = inputs: inputs in a flake, returning inputs for inspection. I guess the missing part in your code is the follows that can be just { }, with-inputs does auto-follows from the flake dependencies so in most cases you don't need to specify follows unless deps use uncommon names.

[aanderse]

thanks for your help so far @vic - and apologies for the delay, i am traveling so a little bit slower to respond than i would like

i didn't know about with-inputs and i am very curious about it! looks like an amazing project.

if i have a dependency on flake a but not flake b, and flake a has a dependent on flake b does this mean i need to add flake b to my list of things to fetch and then override the follow?

[vic]

if i have a dependency on flake a but not flake b, and flake a has a dependent on flake b does this mean i need to add flake b to my list of things to fetch and then override the follow?

Not necessarily, that is the point of not using flakes (for me), I don't want all inputs of my dependencies to be downloaded, for example, some flakes like nix-unit have a dependency on nix-github-actions that I don't need to download.

So if I have a pinned nix-unit, I can use it without having nix-github-actions as long as the code path does not try to evaluate that.

So if you have no flake b it is just like if you had this:

with-inputs sources { a.inputs.b.follows = ""; } outputs;

that one explicitly disables a.inputs.b, but same happens if b is not part of sources automatically.

[aanderse]

right, understood. but my question was about scenarios where flake a definitely needs flake b - the idea is that i should fetch it, right?

[vic]

Oh yes, in that case b needs to be at sources, or

# follows.nix
inputs:
{
   a.inputs = {
     b.follows = "b-with-other-name-at-sources";
     
     # or directly implement a shim for it 
     b.lib = n: n + 1;
     
     # or provide an alternative outPath (eg, another fetcher)
     b = if pathExists /my/b then { outPath = /my/b; } else inputs.nixpkgs.lib.fetchFromFoo { ... };

     # or adapt the `b` from source
     b = source: source // { rev = "HEAD"; };
   };
}

In my personal infra I use vic/flake-file that allows me to automatically extract input definitions from my modules and writes them to npins, I might also add support at flake-file for Lon since it looks very similar to npins.

[aanderse]

amazing. i want to try and port my config to this. i will do so once i get a chance.

[aanderse]

i am very happy to recommend this project. great work @vic !