fix cmp mappings, add snippy

.config/nix-darwin/modules/darwin/nixvim.nix

@@ -24,6 +24,8 @@
 
       nerdtree
 
+      nvim-snippy
+
       (pkgs.vimUtils.buildVimPlugin {
         name = "vim-jjdescription";
         src = pkgs.fetchFromGitHub {
@@ -77,16 +79,58 @@
         enable = true;
         autoEnableSources = true;
         settings = {
-          mapping.__raw = "cmp.mapping.preset.insert({})";
+          snippet.expand = "function(args) require('snippy').expand_snippet(args.body) end";
+          mapping.__raw = ''
+            cmp.mapping.preset.insert({
+              ["<Tab>"] = cmp.mapping(function(fallback)
+                local has_words_before = function()
+                  unpack = unpack or table.unpack
+                  local line, col = unpack(vim.api.nvim_win_get_cursor(0))
+                  return col ~= 0 and vim.api.nvim_buf_get_lines(0, line - 1, line, true)[1]:sub(col, col):match("%s") == nil
+                end
+
+                if cmp.visible() then
+                  cmp.select_next_item()
+                elseif require('snippy').can_expand_or_advance() then
+                  require('snippy').expand_or_advance()
+                elseif has_words_before() then
+                  cmp.complete()
+                else
+                  fallback()
+                end
+                end, {"i", "s"}),
+              ["<S-Tab>"] = cmp.mapping(function(fallback)
+                if cmp.visible() then
+                  cmp.select_prev_item()
+                elseif require('snippy').can_jump(-1) then
+                  require('snippy').previous()
+                else
+                  fallback()
+                end
+              end, {"i", "s"}),
+              ["<CR>"] = cmp.mapping({
+                i = function(fallback)
+                  if cmp.visible() and cmp.get_active_entry() then
+                    cmp.confirm({ behavior = cmp.ConfirmBehavior.Replace, select = true })
+                  else
+                    fallback()
+                  end
+                end,
+                s = cmp.mapping.confirm({ select = true }),
+                c = cmp.mapping.confirm({ behavior = cmp.ConfirmBehavior.Replace, select = true }),
+              })
+            })
+          '';
           sources = [
             { name = "nvim_lsp"; }
             { name = "path"; }
             { name = "buffer"; }
+            { name = "snippy"; }
           ];
         };
         cmdline = {
           ":" = {
-            mapping = { __raw = "cmp.mapping.preset.cmdline()"; };
+            mapping.__raw = "cmp.mapping.preset.cmdline()";
             sources = [
               { name = "path"; }
               { name = "cmdline"; }