theme/habamax: add neovim builtin theme habamax

Author: snoweuph

docs/manual/release-notes/rl-0.9.md

@@ -150,3 +150,5 @@
 
 - Added [Selenen](https://github.com/kampfkarren/selene) for more diagnostics in
   `languages.lua`.
+
+- Added neovim builtin theme `habamax`.

modules/plugins/theme/supported-themes.nix

@@ -8,6 +8,10 @@
   inherit (lib.trivial) boolToString warnIf;
   inherit (lib.nvim.lua) toLuaObject;
 in {
+  habamax = {
+    builtin = true;
+    setup = _: "vim.cmd('colorscheme habamax')";
+  };
   base16 = {
     setup = {base16-colors, ...}: ''
       -- Base16 theme

modules/plugins/theme/theme.nix

@@ -65,7 +65,10 @@ in {
 
   config = mkIf cfg.enable {
     vim = {
-      startPlugins = [cfg.name];
+      startPlugins =
+        if (supportedThemes.${cfg.name} ? builtin) && supportedThemes.${cfg.name}.builtin
+        then []
+        else [cfg.name];
       luaConfigRC.theme = entryBefore ["pluginConfigs" "lazyConfigs"] ''
         ${cfg.extraConfig}
         ${supportedThemes.${cfg.name}.setup {inherit (cfg) style transparent base16-colors;}}