A return can have at most 254 values

lcode.c

@@ -208,6 +208,8 @@ void luaK_ret (FuncState *fs, int first, int nret) {
     case 1: op = OP_RETURN1; break;
     default: op = OP_RETURN; break;
   }
+  if (nret + 1 > MAXARG_B)
+    luaX_syntaxerror(fs->ls, "too many returns");
   luaK_codeABC(fs, op, first, nret + 1, 0);
 }
 

testes/calls.lua

@@ -518,5 +518,16 @@ do   -- check reuse of strings in dumps
   end
 end
 
+
+do   -- test limit of multiple returns (254 values)
+  local code = "return 10" .. string.rep(",10", 253)
+  local res = {assert(load(code))()}
+  assert(#res == 254 and res[254] == 10)
+
+  code = code .. ",10"
+  local status, msg = load(code)
+  assert(not status and string.find(msg, "too many returns"))
+end
+
 print('OK')
 return deep