nixvim: add diffview, gitsigns, which-key. re-enable treesitter. document some keymaps

modules/home/nixvim/plugins/diffview.nix

@@ -0,0 +1,59 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.programs.nixvim;
+  plugin = cfg.plugins.diffview;
+
+  inherit (lib) mkDefault mkIf;
+in
+{
+  config = {
+    programs.nixvim = {
+      plugins.diffview = {
+        enable = mkDefault true;
+      };
+
+      # highlight = mkIf plugin.enable {
+      #   DiffAdd = {
+      #     bg = "#2d4a2d";
+      #     fg = "NONE";
+      #   };
+      #   DiffDelete = {
+      #     bg = "#4a2d2d";
+      #     fg = "NONE";
+      #   };
+      #   DiffChange = {
+      #     bg = "#2d3a4a";
+      #     fg = "NONE";
+      #   };
+      #   DiffText = {
+      #     bg = "#1a5a1a";
+      #     fg = "NONE";
+      #   };
+      # };
+
+      keymaps = mkIf plugin.enable [
+        {
+          mode = "n";
+          key = "<leader>gd";
+          action.__raw = ''
+            function()
+              local lib = require("diffview.lib")
+              local view = lib.get_current_view()
+              if view then
+                vim.cmd("DiffviewClose")
+              else
+                vim.cmd("DiffviewOpen")
+              end
+            end
+          '';
+          options = {
+            noremap = true;
+            silent = true;
+            desc = "toggle git diff";
+          };
+        }
+      ];
+    };
+  };
+}