feat(snippets/luasnip): allow custom snippets

modules/plugins/snippets/luasnip/config.nix

@@ -1,11 +1,48 @@
 {
   config,
   lib,
+  pkgs,
   ...
 }: let
   inherit (lib.modules) mkIf;
 
+  inherit (lib.lists) replicate;
+  inherit
+    (lib.strings)
+    optionalString
+    removeSuffix
+    concatStrings
+    stringAsChars
+    concatMapStringsSep
+    ;
+  inherit (lib.attrsets) mapAttrsToList;
+  inherit (pkgs) writeTextFile;
   cfg = config.vim.snippets.luasnip;
+  # LuaSnip freaks out if the indentation is wrong in snippets
+  indent = n: s: let
+    indentString = concatStrings (replicate n " ");
+    sep = "\n" + indentString;
+  in
+    indentString
+    + stringAsChars (c:
+      if c == "\n"
+      then sep
+      else c) (removeSuffix "\n" s);
+  customSnipmateSnippetFiles =
+    mapAttrsToList (
+      name: value:
+        writeTextFile {
+          name = "${name}.snippets";
+          text =
+            concatMapStringsSep "\n" (x: ''
+              snippet ${x.trigger} ${x.description}
+              ${indent 2 x.body}
+            '')
+            value;
+          destination = "/snippets/${name}.snippets";
+        }
+    )
+    cfg.customSnippets.snipmate;
 in {
   config = mkIf cfg.enable {
     vim = {
@@ -19,11 +56,16 @@ in {
 
         after = cfg.loaders;
       };
-      startPlugins = cfg.providers;
+      startPlugins = cfg.providers ++ customSnipmateSnippetFiles;
       autocomplete.nvim-cmp = mkIf config.vim.autocomplete.nvim-cmp.enable {
         sources = {luasnip = "[LuaSnip]";};
         sourcePlugins = ["cmp-luasnip"];
       };
+      snippets.luasnip.loaders = ''
+        ${optionalString (
+          cfg.customSnippets.snipmate != {}
+        ) "require('luasnip.loaders.from_snipmate').lazy_load()"}
+      '';
     };
   };
 }