Describe the bug
The ebook reader in Calibre 4.0 and above requires PyQtWebEngine for the ebook reader, as it will otherwise throw an ImportError.

To Reproduce
Steps to reproduce the behavior:

1. Install calibre from latest unstable nixpkgs.
2. Run calibre from terminal.
3. Attempt to open an ebook in the viewer (the quick start guide included should work fine for this example)
4. View the error in the terminal.

Expected behavior
The ebook reader to open properly.

Additional context
On my system, I have made an overlay which adds python27.pyqtwebengine to the buildInputs of calibre, and in the resulting derivation the ebook reader works perfectly fine. This seems just to be a missing dependency issue.

Metadata

• system: "x86_64-linux"
• host os: Linux 4.19.97, NixOS, 19.09.1957.57c35c63004 (Loris)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.2
• channels(root): "nixos-19.09.1957.57c35c63004, home-manager-19.09, nixos-unstable-20.03pre210078.90441b4b47f, nur"
• channels(malset): ""
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

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