moonix/modules/theme.nix

# ABOUTME: GTK, Qt, Kvantum, Plymouth, cursors and fonts — the look, in one place.
# ABOUTME: Same theme derivations the greeter uses, so the two cannot drift apart.

{ pkgs, moonarchSrc, moonarchPkgs, moonarchThemes, ... }:

let
  xdg = "${moonarchSrc}/defaults/xdg";

  # The GTK theme name, in the one place both consumers below read it from.
  gtkTheme = "catppuccin-mocha-lavender-standard";

  # Both distributions ship the same Catppuccin GTK theme, 1.0.3, and still
  # disagree on its name — permanently, not as a migration. Arch installs the
  # upstream release zips through catppuccin-gtk-theme-mocha, whose directories
  # carry the full build name with the `+default` tweak marker; nixpkgs builds
  # the same source with no tweaks and so names it without that suffix. Neither
  # side can adopt the other's name without going out of its way.
  #
  # The rewrite therefore has to stay. It matters because GTK3 reads
  # settings.ini directly — the dconf entry further down only reaches
  # applications that ask GSettings, which on Wayland the GTK3 ones do not — so
  # a name that does not resolve puts every GTK3 application on Adwaita, with
  # no error anywhere.
  gtkSettings = version: pkgs.runCommand "gtk${version}-settings.ini" { } ''
    substitute ${xdg}/gtk-${version}/settings.ini "$out" \
      --replace-fail catppuccin-mocha-lavender-standard+default ${gtkTheme}
  '';

  # The theme deployed Kvantum/kvantum.kvconfig selects. It goes into
  # systemPackages: nixpkgs patches Kvantum to search XDG_DATA_DIRS for themes
  # (tsujan/Kvantum 01989083, in the package's patches list), and
  # /run/current-system/sw/share is on that path, so a theme package is found
  # system-wide with nothing seeded into the home directory.
  #
  # Verified under strace: a Qt6 client opens the theme's .kvconfig straight
  # out of the package's store path. The patch only takes in the Qt6 build
  # (NixOS/nixpkgs#355277) — a Qt5 client searches four roots instead:
  # ~/.config/Kvantum, ~/.themes, ~/.local/share/themes and its own store path.
  # The tmpfiles rule further down puts the theme in the first of them, which is
  # where the published solutions for this put it.
  kvantumTheme = pkgs.catppuccin-kvantum.override {
    accent = "lavender";
    variant = "mocha";
  };

  # The theme name as both the package directory and the .kvconfig entry spell
  # it, so the link target below cannot drift from what Kvantum looks up.
  kvantumThemeName = "catppuccin-mocha-lavender";

in
{
  environment.etc = {
    "xdg/Kvantum/kvantum.kvconfig".source = "${xdg}/Kvantum/kvantum.kvconfig";
    "xdg/qt6ct/qt6ct.conf".source = "${xdg}/qt6ct/qt6ct.conf";

    # No counterpart in moonarch's defaults: Arch ships qt5ct's own config, and
    # this file only has to exist because Qt5 and Qt6 read one variable between
    # them, see QT_QPA_PLATFORMTHEME below. Same settings as qt6ct.conf.
    "xdg/qt5ct/qt5ct.conf".text = ''
      # ABOUTME: System qt5ct config — Qt5 icon theme + Kvantum style, matching qt6ct.conf.
      # ABOUTME: Deployed to /etc/xdg/qt5ct/qt5ct.conf; a user copy in ~/.config/qt5ct wins by XDG precedence.
      [Appearance]
      style=kvantum
      icon_theme=Colloid-Grey-Catppuccin-Dark
      standard_dialogs=default
    '';
    "xdg/gtk-3.0/settings.ini".source = gtkSettings "3.0";
    "xdg/gtk-4.0/settings.ini".source = gtkSettings "4.0";
  };

  # Generic-family defaults. Same content as
  # defaults/etc/fonts/conf.d/65-moonarch-fonts.conf, but routed through the
  # fontconfig module: /etc/fonts/conf.d/ is owned by NixOS and rejects
  # environment.etc entries.
  # localConf is written to /etc/fonts/local.conf verbatim, so it has to be a
  # complete XML document — not just the inner elements.
  fonts.fontconfig.localConf = ''
    <?xml version="1.0"?>
    <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
    <fontconfig>
      <description>Moonarch generic-family defaults</description>
      <!-- binding="strong" required: the default weak <prefer> ranks behind
           stock generic fallbacks, so it would not take effect. -->
      <alias binding="strong">
        <family>sans-serif</family>
        <prefer>
          <family>UbuntuSans Nerd Font</family>
        </prefer>
      </alias>
      <alias binding="strong">
        <family>monospace</family>
        <prefer>
          <family>UbuntuSansMono Nerd Font</family>
        </prefer>
      </alias>
    </fontconfig>
  '';

  # Set systemwide instead of through the gsettings calls in post-install.sh.
  programs.dconf = {
    enable = true;
    profiles.user.databases = [{
      settings."org/gnome/desktop/interface" = {
        gtk-theme = gtkTheme;
        icon-theme = "Colloid-Grey-Catppuccin-Dark";
        color-scheme = "prefer-dark";
        font-name = "UbuntuSans Nerd Font 11";
      };
    }];
  };

  # The boot splash. `quiet` is already on the kernel command line and the module
  # puts `splash` there itself, so nothing else has to change for it to show.
  # With systemd in the initrd, which this configuration uses, systemd asks for
  # the LUKS passphrase and Plymouth draws that prompt; the script initrd instead
  # shows it as text before the splash comes up.
  # The theme carries a name of its own, outside the catppuccin-<flavour> set
  # that the NixOS plymouth module links its logo into, so the splash shows
  # what the theme brings and nothing besides.
  boot.plymouth = {
    enable = true;
    theme = "moonarch";
    themePackages = [ moonarchPkgs.moonarch-plymouth ];
  };

  # Qt applications are wrapped, so each one looks for plugins in its own
  # closure and never finds a style installed alongside it — which is why VLC
  # kept coming up in the stock Qt style. Enabling this puts the profile's Qt5
  # and Qt6 plugin directories on QT_PLUGIN_PATH, which the wrappers append to.
  # platformTheme and style stay null: it would add packages that are already
  # listed below, and niri's environment block sets both variables already.
  qt.enable = true;

  fonts.packages = with pkgs; [
    nerd-fonts.ubuntu-sans
    openmoji-color
  ];

  # niri sets both in its own environment block, but that only reaches what niri
  # itself spawns. Anything under the systemd user manager — quickshell, and so
  # everything started from its launcher — never sees them, and Qt applications
  # come up unstyled. Set here they travel through /etc/profile into
  # niri-session's import-environment, and from there into the user manager.
  # qt5ct, not qt6ct: Qt5 and Qt6 both read this one variable, and a Qt5 client
  # asked for "qt6ct" finds only a Qt6 plugin it cannot load, so it comes up
  # with no platform theme at all — no icon theme, no fonts, stock dialogs.
  # Under "qt5ct" each version loads the plugin built for it; that pairing is
  # what nixpkgs ships as qt.platformTheme "qt5ct", which installs both.
  environment.sessionVariables.QT_QPA_PLATFORMTHEME = "qt5ct";
  environment.sessionVariables.QT_STYLE_OVERRIDE = "kvantum";

  # Same gap, cursors: niri's cursor block reaches xwayland-satellite, so X11
  # clients have a themed pointer available, but everything under the user
  # manager arrives with XCURSOR_PATH alone and has no theme name to look up.
  # The name matches modules/greetd.nix, so greeter and session agree.
  environment.sessionVariables.XCURSOR_THEME = "Sweet-cursors";
  environment.sessionVariables.XCURSOR_SIZE = "24";

  # systemPackages alone does not put the theme on XDG_DATA_DIRS: the system
  # path links only the /share subdirectories named here, and Kvantum's is not
  # among the defaults.
  environment.pathsToLink = [ "/share/Kvantum" ];

  systemd.user.tmpfiles.rules = [
    # Steam gets XCURSOR_THEME from the block above — verified in its own
    # environment — and still drew the core pointer, so parts of it resolve the
    # theme literally named 'default' rather than the variable. Xcursor looks
    # that name up along XCURSOR_PATH like any other, and ~/.icons is first,
    # so pointing it at the theme covers those lookups too. 'L+' replaces the
    # link on every activation, unlike the 'C' rules elsewhere, which keeps it
    # following the theme instead of freezing at today's one.
    "L+ %h/.icons/default - - - - /run/current-system/sw/share/icons/Sweet-cursors"

    # Kvantum's Qt5 build never looks at XDG_DATA_DIRS, so the theme installed
    # system-wide is invisible to it; ~/.config/Kvantum is the first place it
    # does look. 'L+' for the same reason as the rule above: the link follows
    # the system profile instead of freezing at one store path.
    "L+ %h/.config/Kvantum/${kvantumThemeName} - - - - /run/current-system/sw/share/Kvantum/${kvantumThemeName}"
  ];

  environment.systemPackages = with pkgs; [
    moonarchPkgs.sweet-cursors

    # Theming. Same derivations the greeter uses, see flake.nix.
    moonarchThemes.gtk
    moonarchThemes.icons
    libsForQt5.qtstyleplugin-kvantum
    qt6Packages.qtstyleplugin-kvantum
    kvantumTheme
    libsForQt5.qt5ct
    qt6Packages.qt6ct
    qt6.qt5compat

    # GTK settings editor; it writes the same settings.ini this module deploys.
    nwg-look
  ];
}