prefer-remote-fetch: fix fetchurl eval

[SuperSandro2000]

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[ShamrockLee]

Sorry, I forgot to consider that args might be a function when writing args.prefenLocalBuild or false.
It should be

Suggested change

	fetchurl = args: super.fetchurl (super.lib.extends
	(super.lib.toExtension { preferLocalBuild = args.preferLocalBuild or false; })
	(super.lib.toFunction args));
	fetchurl = fpArgs: super.fetchurl (super.lib.extends
	(finalAttrs: args: { preferLocalBuild = args.preferLocalBuild or false; })
	(super.lib.toFunction fpArgs));

Or,

Suggested change

	fetchurl = args: super.fetchurl (super.lib.extends
	(super.lib.toExtension { preferLocalBuild = args.preferLocalBuild or false; })
	(super.lib.toFunction args));
	fetchurl = lib.extendMkDerivation {
	constructDrv = previous.fetchurl;
	extendDrvArgs = finalAttrs: args: { preferLocalBuild = args.preferLocalBuild or false; };
	}

The latter handles the __functionArgs automatically.

[SuperSandro2000]

The 2nd failed with:

error:
       … while calling the 'head' builtin
         at /home/sandro/src/nixpkgs/lib/attrsets.nix:1696:13:
         1695|           if length values == 1 || pred here (elemAt values 1) (head values) then
         1696|             head values
             |             ^
         1697|           else

       … while evaluating the attribute 'value'
         at /home/sandro/src/nixpkgs/lib/modules.nix:1118:7:
         1117|     // {
         1118|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |       ^
         1119|       inherit (res.defsFinal') highestPrio;

       … while evaluating the option `system.build.toplevel':

       … while evaluating definitions from `/nix/store/p5jrkni7q6pa7ckfyqrrjysqh8i5nmdf-source/nixos/modules/system/activation/top-level.nix':

       … while evaluating the option `system.activationScripts':

       … while evaluating definitions from `/nix/store/6mis9m031ia3c7fmxh3gqrq4782dmppn-source/modules/ssh.nix':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: function 'extendDrvArgs' called with unexpected argument 'prefetchLocalBuild'
       at /home/sandro/src/nixpkgs/pkgs/build-support/fetchurl/default.nix:72:5:
           71|     finalAttrs:
           72|     {
             |     ^
           73|       # URL to fetch.

[ShamrockLee]

The 2nd failed with:

That's due to a typo. It should be preferLocalBuild instead of prefetchLocalBuild.

[ShamrockLee]

Updated. Sorry for the trouble.

[philiptaron]

Wow, this is convoluted.

Is there a test for these derivation mutators (a phrase I just made up) @SuperSandro2000 that I should run to make sure it's not broken?

[SuperSandro2000]

Probably not but it would probably be as easy as just evalling pkgs with it as an overlay

[Mic92]

Maybe it can be added to lib-tests?