nixos/plymouth: use bgrt theme

The BGRT theme is probably a close as to "FlickerFree" we can
get without https://github.com/NixOS/nixpkgs/pull/74842.
It's more agnostic than the Breeze theme.

We also install all of themes provided by the packages, as it's possible
that one theme needs the ImageDir of another, and they're small files
anyways.

Lastly, how plymouth handles logo and header files is
a total mess, so hopefully when they have an actual release
we won't need to do all this symlinking.

nixos/modules/system/boot/plymouth.nix

@@ -4,8 +4,7 @@ with lib;
 
 let
 
-  inherit (pkgs) plymouth;
-  inherit (pkgs) nixos-icons;
+  inherit (pkgs) plymouth nixos-icons;
 
   cfg = config.boot.plymouth;
 
@@ -16,9 +15,31 @@ let
     osVersion = config.system.nixos.release;
   };
 
+  plymouthLogos = pkgs.runCommand "plymouth-logos" { inherit (cfg) logo; } ''
+    mkdir -p $out
+
+    # For themes that are compiled with PLYMOUTH_LOGO_FILE
+    mkdir -p $out/etc/plymouth
+    ln -s $logo $out/etc/plymouth/logo.png
+
+    # Logo for bgrt theme
+    # Note this is technically an abuse of watermark for the bgrt theme
+    # See: https://gitlab.freedesktop.org/plymouth/plymouth/-/issues/95#note_813768
+    mkdir -p $out/share/plymouth/themes/spinner
+    ln -s $logo $out/share/plymouth/themes/spinner/watermark.png
+
+    # Logo for spinfinity theme
+    # See: https://gitlab.freedesktop.org/plymouth/plymouth/-/issues/106
+    mkdir -p $out/share/plymouth/themes/spinfinity
+    ln -s $logo $out/share/plymouth/themes/spinfinity/header-image.png
+  '';
+
   themesEnv = pkgs.buildEnv {
     name = "plymouth-themes";
-    paths = [ plymouth ] ++ cfg.themePackages;
+    paths = [
+      plymouth
+      plymouthLogos
+    ] ++ cfg.themePackages;
   };
 
   configFile = pkgs.writeText "plymouthd.conf" ''
@@ -48,7 +69,7 @@ in
       };
 
       themePackages = mkOption {
-        default = [ nixosBreezePlymouth ];
+        default = lib.optional (cfg.theme == "breeze") nixosBreezePlymouth;
         type = types.listOf types.package;
         description = ''
           Extra theme packages for plymouth.
@@ -56,7 +77,7 @@ in
       };
 
       theme = mkOption {
-        default = "breeze";
+        default = "bgrt";
         type = types.str;
         description = ''
           Splash screen theme.
@@ -111,12 +132,12 @@ in
     systemd.services.plymouth-poweroff.wantedBy = [ "poweroff.target" ];
     systemd.services.plymouth-reboot.wantedBy = [ "reboot.target" ];
     systemd.services.plymouth-read-write.wantedBy = [ "sysinit.target" ];
-    systemd.services.systemd-ask-password-plymouth.wantedBy = ["multi-user.target"];
-    systemd.paths.systemd-ask-password-plymouth.wantedBy = ["multi-user.target"];
+    systemd.services.systemd-ask-password-plymouth.wantedBy = [ "multi-user.target" ];
+    systemd.paths.systemd-ask-password-plymouth.wantedBy = [ "multi-user.target" ];
 
     boot.initrd.extraUtilsCommands = ''
-      copy_bin_and_libs ${pkgs.plymouth}/bin/plymouthd
-      copy_bin_and_libs ${pkgs.plymouth}/bin/plymouth
+      copy_bin_and_libs ${plymouth}/bin/plymouth
+      copy_bin_and_libs ${plymouth}/bin/plymouthd
 
       # Check if the actual requested theme is here
       if [[ ! -d ${themesEnv}/share/plymouth/themes/${cfg.theme} ]]; then
@@ -134,21 +155,29 @@ in
       mkdir -p $out/share/plymouth/themes
       cp ${plymouth}/share/plymouth/plymouthd.defaults $out/share/plymouth
 
-      # copy themes into working directory for patching
+      # Copy themes into working directory for patching
       mkdir themes
-      # use -L to copy the directories proper, not the symlinks to them
-      cp -r -L ${themesEnv}/share/plymouth/themes/{text,details,${cfg.theme}} themes
 
-      # patch out any attempted references to the theme or plymouth's themes directory
+      # Use -L to copy the directories proper, not the symlinks to them.
+      # Copy all themes because they're not large assets, and bgrt depends on the ImageDir of
+      # the spinner theme.
+      cp -r -L ${themesEnv}/share/plymouth/themes/* themes
+
+      # Patch out any attempted references to the theme or plymouth's themes directory
       chmod -R +w themes
       find themes -type f | while read file
       do
         sed -i "s,/nix/.*/share/plymouth/themes,$out/share/plymouth/themes,g" $file
       done
 
+      # Install themes
       cp -r themes/* $out/share/plymouth/themes
-      cp ${cfg.logo} $out/share/plymouth/logo.png
 
+      # Install logo
+      mkdir -p $out/etc/plymouth
+      cp -r -L ${themesEnv}/etc/plymouth $out
+
+      # Setup font
       mkdir -p $out/share/fonts
       cp ${cfg.font} $out/share/fonts
       mkdir -p $out/etc/fonts