Add C/C++ include guard snippet 'once'

snippets/c.lua

@@ -7,6 +7,11 @@ local insert = luasnip.insert_node
 local func = luasnip.function_node
 local key = require("luasnip.nodes.key_indexer").new_key
 
+local function getIncludeGuardName()
+  local filename = vim.fn.expand('%'):gsub('[^%w_]', '_'):upper()
+  return filename .. '_INCLUDED'
+end
+
 local snippets = {
   snip('#include', {
     text('#include '),
@@ -20,6 +25,21 @@ local snippets = {
       end
     end, key('open')),
   }),
+
+  snip('once', {
+    text('#ifndef '),
+    func(function(args)
+      return args[1][1]
+    end, key('name')),
+    text({ '', '#define ' }),
+    insert(1, getIncludeGuardName(), { key = 'name' }),
+    text({ '', '', '', }),
+    insert(0, ''),
+    text({ '', '', '#endif  // ' }),
+    func(function(args)
+      return args[1][1]
+    end, key('name')),
+  }),
 }
 
 return snippets