More interesting dyn drv test case

[Ericson2314]

Motivation

The existing ones did not shine enough light on this feature.

Context

depends on #9415

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[Ericson2314]

I'm not saying we should def add python to the testsuite deps, but this is a lot easier to read:

with import ./config.nix;

builtins.outputOf (mkDerivation {
  name = "make-derivations.drv";

  requiredSystemFeatures = [ "recursive-nix" ];

  buildCommand = ''
    import os
    import json
    import subprocess

    os.environ["PATH"] = os.pathsep.join([os.getenv("NIX_BIN_DIR", ""), os.environ["PATH"]])
    os.environ["NIX_CONFIG"] = "extra-experimental-features = nix-command ca-derivations dynamic-derivations"

    deps = {
        "a": [],
        "b": ["a"],
        "c": ["a"],
        "d": ["b", "c"],
        "e": ["b", "c", "d"],
    }

    # Cannot just literally include this, or Nix will think it is the
    # *outer* derivation that's trying to refer to itself, and
    # substitute the string too soon.
    placeholder = subprocess.check_output(["nix", "eval", "--raw", "--expr", "builtins.placeholder \"out\""]).decode().strip()

    drvs = {}
    for word in ["a", "b", "c", "d", "e"]:
        input_drvs = {}

        for dep in deps[word]:
            input_drvs[drvs[dep]] = {
                "outputs": ["out"],
                "dynamicOutputs": {},
            }

        json_data = {
            "args": ["-c", f"set -xeu; echo \"word env var {word} is ${word}\" >> \"$out\""],
            "builder": os.environ["shell"],
            "env": {
                "out": placeholder,
                word: f"hello, from {word}!",
                "PATH": json.dumps(os.environ["PATH"]),
            },
            "inputDrvs": input_drvs,
            "inputSrcs": [],
            "name": f"build-{word}",
            "outputs": {
                "out": {
                    "method": "nar",
                    "hashAlgo": "sha256",
                },
            },
            "system": os.environ["system"],
        }

        drvs[word] = subprocess.check_output(["nix", "derivation", "add"], input=json.dumps(json_data).encode()).decode().strip()

    with open(os.environ["out"], "w") as out_file:
        out_file.write(drvs["e"])
  '';

  __contentAddressed = true;
  outputHashMode = "text";
  outputHashAlgo = "sha256";
}).outPath "out"

(thank you chat gpt)

[roberth]

I wouldn't mind having python in the test suite, as it is already part of the build anyway. It doesn't increase the bootstrapping closure, and tests are not required for that anyway (as if a second argument is relevant)

[roberth]

If this is a common occurrence, I guess we could create placeholders that unwrap into other placeholders.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-02-12-nix-team-meeting-minutes-212-5/60216/1