Make table.append() behave as table.insert() with nil

Fixes #72

Author: HaroldCindy

VM/src/ltablib.cpp

@@ -237,20 +237,18 @@ static int tmove(lua_State* L)
 }
 
 // ServerLua: table.append(t, ...) - appends varargs to end of table
-// Largely a replacement for consecutive `table.insert()` calls.
+// Semantically equivalent to consecutive `table.insert()` calls.
 static int tappend(lua_State* L)
 {
-    // Need some extra slots for actually appending
     lua_checkstack(L, 2);
 
     luaL_checktype(L, 1, LUA_TTABLE);
-    int orig_len = lua_objlen(L, 1);
     int top = lua_gettop(L);
 
     for (int i = 2; i <= top; i++)
     {
         lua_pushvalue(L, i);
-        lua_rawseti(L, 1, orig_len + (i - 1));
+        lua_rawseti(L, 1, lua_objlen(L, 1) + 1);
     }
 
     return 0;

tests/conformance/tables.luau

@@ -825,6 +825,20 @@ do
 
   -- returns nil
   assert(table.append({1}, 2) == nil)
+
+  -- Is semantically equivalent to repeated `table.insert()`
+  -- (i.e. it implicitly skips `nil` and respects existing holes
+  t5 = table.create(3)
+  t5[5] = 5
+  t5[1] = 1
+  t5[2] = 2
+  assert(#t5 == 2)
+  -- `nil`s are basically no-ops, as they would be in `table.insert()`
+  table.append(t5, 3, 4, nil, nil, nil, 6)
+  assert(#t5 == 6)
+
+  -- Eesh, wish there was lljson here.
+  assert(t5[3] == 3 and t5[4] == 4 and t5[5] == 5 and t5[6] == 6 and t5[7] == nil)
 end
 
 -- ServerLua: table.extend