neovim: Support configuring plugins using Fennel

PR #2637 added a 'type' field denoting the language used to configure
neovim plugins. However, when the type is set to "fennel" or "teal"
the configuration is silently ignored.

This commit enables support for Fennel by transpiling it to Lua before
appending the generated code to `init.lua`.

This commit __does not__ provide spport for configs written in Teal;
they are still silently ignored.

modules/programs/neovim/default.nix

@@ -21,7 +21,7 @@ let
 
   inherit
     (
-      (import ../lib/file-type.nix {
+      (import ../../lib/file-type.nix {
         inherit (config.home) homeDirectory;
         inherit lib pkgs;
       })
@@ -50,6 +50,7 @@ in
   meta.maintainers = with lib.maintainers; [ khaneliman ];
 
   imports = [
+    ./fennel.nix
     (lib.mkRenamedOptionModule
       [ "programs" "neovim" "extraLuaConfig" ]
       [ "programs" "neovim" "initLua" ]

modules/programs/neovim/fennel.nix

@@ -0,0 +1,40 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.programs.neovim;
+in
+{
+  config = lib.mkIf cfg.enable {
+    programs.neovim.initLua =
+      lib.mkIf (lib.hasAttr "fennel" cfg.generatedConfigs && cfg.generatedConfigs.fennel != "")
+        (
+          lib.mkAfter ''
+            -- user-associated fennel plugin config {{{
+            require('fennel-plugins')
+            -- }}}
+          ''
+        );
+
+    xdg.configFile."nvim/lua/fennel-plugins.lua" =
+      let
+        compiledFennel =
+          pkgs.runCommand "fennel-plugins.lua"
+            {
+              fnlSrc = cfg.generatedConfigs.fennel;
+              __structuredAttrs = true;
+            }
+            ''
+              ${lib.getExe pkgs.jq} -rj '.fnlSrc' "$NIX_ATTRS_JSON_FILE" > fnlSrc
+              ${lib.getExe cfg.package.lua.pkgs.fennel} --compile fnlSrc > "$out"
+            '';
+      in
+      lib.mkIf (lib.hasAttr "fennel" cfg.generatedConfigs && cfg.generatedConfigs.fennel != "") {
+        source = compiledFennel;
+      };
+  };
+}

tests/modules/programs/neovim/default.nix

@@ -9,4 +9,5 @@
   neovim-extra-lua-default = ./extra-lua-default.nix;
   neovim-extra-lua-empty-plugin = ./extra-lua-empty-plugin.nix;
   neovim-plugin-type-warning = ./plugin-type-warning.nix;
+  neovim-fennel-plugin-config = ./plugin-fennel-config.nix;
 }

tests/modules/programs/neovim/plugin-fennel-config.nix

@@ -0,0 +1,36 @@
+{
+  config,
+  lib,
+  pkgs,
+  realPkgs,
+  ...
+}:
+
+lib.mkIf config.test.enableBig {
+  programs.neovim = {
+    enable = true;
+    withRuby = false;
+    plugins = with pkgs.vimPlugins; [
+      {
+        plugin = vim-nix;
+        type = "fennel";
+        config = ''(vim.cmd "let g:hmFennelPlugin='HM_FENNEL_PLUGIN'")'';
+      }
+    ];
+  };
+
+  _module.args.pkgs = lib.mkForce realPkgs;
+
+  nmt.script = ''
+    export PATH="$TESTED/home-path/bin:$PATH"
+    export HOME=$TMPDIR/hm-user
+    export XDG_CONFIG_HOME="$TESTED/home-files/.config"
+    initLua="$TESTED/home-files/.config/nvim/init.lua"
+
+    assertFileContains "$initLua" "require('fennel-plugins')"
+
+    vimout=$(mktemp)
+    nvim --headless +'lua print(vim.g.hmFennelPlugin)' +q! 2&> $vimout
+    assertFileContains "$vimout" "HM_FENNEL_PLUGIN"
+  '';
+}