Add neovim config using nixvim

programs/nixvim/completion.nix

@@ -0,0 +1,65 @@
+{ ... }:
+
+{
+  programs.nixvim = {
+    opts.completeopt = [
+      "menu"
+      "menuone"
+      "noselect"
+    ];
+
+    plugins = {
+      luasnip.enable = true;
+
+      lspkind = {
+        enable = true;
+
+        settings = {
+          cmp = {
+            enable = true;
+            menu = {
+              nvim_lsp = "[LSP]";
+              nvim_lua = "[api]";
+              path = "[path]";
+              luasnip = "[snip]";
+              buffer = "[buffer]";
+              cmp_tabby = "[Tabby]";
+            };
+          };
+        };
+      };
+
+      cmp = {
+        enable = true;
+
+        settings = {
+          snippet.expand = ''
+            function(args)
+              require('luasnip').lsp_expand(args.body)
+            end
+          '';
+
+          mapping = {
+            "<C-d>" = "cmp.mapping.scroll_docs(-4)";
+            "<C-f>" = "cmp.mapping.scroll_docs(4)";
+            "<C-Space>" = "cmp.mapping.complete()";
+            "<C-e>" = "cmp.mapping.close()";
+            "<Tab>" = "cmp.mapping(cmp.mapping.select_next_item(), {'i', 's'})";
+            "<S-Tab>" = "cmp.mapping(cmp.mapping.select_prev_item(), {'i', 's'})";
+            "<CR>" = "cmp.mapping.confirm({ select = true })";
+          };
+
+          sources = [
+            { name = "path"; }
+            { name = "nvim_lsp"; }
+            { name = "luasnip"; }
+            {
+              name = "buffer";
+              option.get_bufnrs.__raw = "vim.api.nvim_list_bufs";
+            }
+          ];
+        };
+      };
+    };
+  };
+}