nixos/matrix: write manual section

[florianjacob]

Motivation for this change

This was developed as part of
#55320 (comment)
with the initial intention to show users how to set up a synapse homeserver with a valid certificate, in light of the upcoming 1.0 release.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[florianjacob]

@Ekleog this is yet missing a changelog entry / edit of the matrix-synapse 1.0 changelog warning you mentioned in #55320 (comment), depending on whether this can still go in 19.03.

[florianjacob]

Other synapse maintainers: @Ralith @roblabla
riot-web maintainer: @bachp

[Ekleog]

@florianjacob As this is a manual change only, I'm pretty sure it'll be OK to backport, so feel free to add a link to the 19.03 changelog :) I'll merge once the link is added and @pacien 's comments are addressed, thanks a lot!

[Ekleog]

Potentially personal opinion ahead: I feel that this let should be after the line break. Feel free to ignore, though, we still don't have any kind of style guide for the time being.

[florianjacob]

You mean like this?

let
  fqdn =
    let
      join = hostName: domain: hostName + optionalString (domain != null) ".${domain}";
    in join config.networking.hostName config.networking.domain;
in {
…
};

Changed to this style now, the other two bindings as well.

I always struggle to format let bindings. :/ Any good example would be appreciated, as almost any let binding you find in nixpkgs is formatted differently… Can't wait for an actual style guide.

[Ekleog]

Looks great this way, thanks! Totally agree we definitely need a style guide; currently the most frequent formattings I see are these, I think (but I'm likely biased by my own personal preferences):

{
  a = let foo = bar; in baz;
  b =
    let foo = bar;
    in baz;
  c =
    let
      foo = bar;
    in baz;
  d =
    let
      foo = bar;
    in
      baz;
  e =
    let
      foo = bar;
    in
    baz; # mostly used to stay at column 0
}

[florianjacob]

Those styles look very reasonable, thank you. 👍

[florianjacob]

Thanks to all for their feedback and review,
@Ekleog just pushed all requested changes, now with changelog entries for 19.03 and link to manual chapter.

[Ekleog]

@florianjacob Thank you! Merged and backported as 4e8ace1. If someone has further issues with this, it can be fixed as an additional PR I think :)