nix-prefetch: fix compatibility with extendMkDerivation-based fetchers

[Titaniumtown]

I was running into the issue, when running ./pkgs/development/python-modules/playwright/update.sh to update playwright. It seemed nix-prefetch didn't like being called on fetchers that used extendMkDerivation, resulting in a "expected a set but found a function" error. Nix-prefetch always assumes that fetcher arguments will always be attribute sets, but in reality we are passing functions to them.

For transparency's sake, I used Claude Opus 4.5 to actually root cause this issue because I didn't have a grasp on the issue I was encountering.

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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[bitbloxhub]

I think these changes make sense and work.

[nixos-discourse]

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

https://discourse.nixos.org/t/prs-already-reviewed/2617/2690

[mdaniels5757]

nixpkgs-review result

Generated using nixpkgs-review-gha

Command: nixpkgs-review pr 470230
Commit: 030e2797323d4f24d335be2c659ec3c1376e4f63 (subsequent changes)
Merge: 4c6d09511fa258125bee36009a4cda78e399fa47

Logs: https://github.com/mdaniels5757/nixpkgs-review-gha/actions/runs/20464688225

Download packages from cache:

• x86_64-linux

  nix-store -r --add-root nixpkgs-pr-470230-x86_64-linux \
    --option binary-caches 'https://cache.nixos.org/ https://mdaniels5757-nix.cachix.org' \
    --option trusted-public-keys '
    cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    mdaniels5757-nix.cachix.org-1:iT2D2XMbTS301DFoC8sTOSP86fXMPiGrvPnrEsQN5uo=
    ' \
    /nix/store/c49wc8029wrv979vy7kc1c1ijghx4nlb-nim_lk-20250309 \
    /nix/store/r97f83y6xr4ji435b4x7kfb459l4rw3p-nix-prefetch-0.4.1

• aarch64-linux

  nix-store -r --add-root nixpkgs-pr-470230-aarch64-linux \
    --option binary-caches 'https://cache.nixos.org/ https://mdaniels5757-nix.cachix.org' \
    --option trusted-public-keys '
    cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    mdaniels5757-nix.cachix.org-1:iT2D2XMbTS301DFoC8sTOSP86fXMPiGrvPnrEsQN5uo=
    ' \
    /nix/store/zqad0qny1p6jm6l8vcan7ylb6y1ch2yc-nim_lk-20250309 \
    /nix/store/bm2f2yf58klndr2jkqlh2yl8vylp5kfp-nix-prefetch-0.4.1

• x86_64-darwin

  nix-store -r --add-root nixpkgs-pr-470230-x86_64-darwin \
    --option binary-caches 'https://cache.nixos.org/ https://mdaniels5757-nix.cachix.org' \
    --option trusted-public-keys '
    cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    mdaniels5757-nix.cachix.org-1:iT2D2XMbTS301DFoC8sTOSP86fXMPiGrvPnrEsQN5uo=
    ' \
    /nix/store/ibkcyq0mlpnrbvbcy5zkm6d81h4qmnri-nim_lk-20250309 \
    /nix/store/0hi5f22him29vhcr2i87s3q2iyb9j8k8-nix-prefetch-0.4.1

• aarch64-darwin

  nix-store -r --add-root nixpkgs-pr-470230-aarch64-darwin \
    --option binary-caches 'https://cache.nixos.org/ https://mdaniels5757-nix.cachix.org' \
    --option trusted-public-keys '
    cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    mdaniels5757-nix.cachix.org-1:iT2D2XMbTS301DFoC8sTOSP86fXMPiGrvPnrEsQN5uo=
    ' \
    /nix/store/rlm55c10yxmkbxiwqwf3k792jrysw25x-nim_lk-20250309 \
    /nix/store/dncixpn8labrbs1k3wy5xvbxfzk94ihz-nix-prefetch-0.4.1

---

x86_64-linux

✅ 2 packages built:

• nim_lk
• nix-prefetch

---

aarch64-linux

✅ 2 packages built:

• nim_lk
• nix-prefetch

---

x86_64-darwin (sandbox = true)

✅ 2 packages built:

• nim_lk
• nix-prefetch

---

aarch64-darwin (sandbox = true)

✅ 2 packages built:

• nim_lk
• nix-prefetch

[mdaniels5757]

Approved automatically following the successful run of nixpkgs-review.