mu: add package option

[jian-lin]

Description

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

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• If this PR adds a new module

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Maintainer CC

@KarlJoad

[jian-lin]

Do you have any ideas why getExe cfg.package evals to @mu@/bin/dummy in test? @rycee @ncfavier

It evals to the right thing: /nix/store/n9v56iqlsi3vlf9dl86p6n2ywszzr85g-mu-1.10.3/bin/mu if I build my NixOS system with this PR.

[jian-lin]

I figured out and fixed the test.

[ravenjoad]

This looks fine to me. But what is the purpose of this change? You left the "Description" box blank at the top of the PR.

[jian-lin]

But what is the purpose of this change?

The purpose is the same as the one of any other package option: making it easy, i.e., not using an overlay, to change the mu package.

My specific use case is to set the package to pkgs.mu.override { emacs = config.services.emacs.package.emacs; } to do native compilation for mu4e with the right Emacs when building mu.

[jian-lin]

FYI, adding a package option seems to be a convention.

[ravenjoad]

Ah. I did not know about that convention. Cool! Thanks for adding it!

[quinn-dougherty]

This gave me another way forward for debugging https://discourse.nixos.org/t/doom-emacs-and-mu4e/21222/3?u=quinn-dougherty -- so thanks!