Describe the bug
In 0b8799e I was faced with the following error when trying to build elisa:

$ nix run -f . elisa
error: Package ‘breeze-qt5-5.18.5’ in /opt/exp/nixpkgs/pkgs/desktops/plasma-5/default.nix:96 is marked as broken, refusing to evaluate.

However, nothing in pkgs/desktops/plasma-5/breeze-qt5.nix suggests that breeze-qt5 is marked as broken. I looked in the "obvious" places, (e.g. all-packages.nix, pkgs/desktops/plasma-5/default.nix) yet have been utterly unable to locate the broken declaration in question. Presumably there is something somewhere which does mark it as broken. However, I haven't the slightest idea how one would find it.

To Reproduce
Steps to reproduce the behavior:

1. Try building a broken derivation
2. Encounter error
3. Try in vain to find the broken attribute

Expected behavior

The error should tell you the source location of the broken attribute.

Screenshots
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Additional context
Add any other context about the problem here.

Notify maintainers

Metadata

 - system: `"x86_64-linux"`
 - host os: `Linux 5.8.14, NixOS, 20.09beta1057.0b8799ecaaf (Nightingale)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.7`
 - channels(root): `"nixos-20.09beta1057.0b8799ecaaf, nixpkgs-20.09beta1057.0b8799ecaaf"`
 - channels(ben): `"nixpkgs-20.09beta1083.51aaa3fa1b6, nixpkgs-20_03-20.03.3122.ff6fda61600, nixpkgs-unstable-21.03pre246624.cfed29bfcb2, nixos-18.09-18.09.2574.a7e559a5504"`
 - nixpkgs: `/home/ben/.nix-defexpr/channels/nixpkgs`

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module: