From 0ad47e19d91dbfc04f890cdbbd09f7cf9f3e9d5f Mon Sep 17 00:00:00 2001
From: daurnimator <quae@daurnimator.com>
Date: Thu, 27 Apr 2017 01:56:56 +1000
Subject: Add a couple of asserts to catch common errors

---
 src/ldo.js  | 1 +
 src/llex.js | 1 +
 2 files changed, 2 insertions(+)

diff --git a/src/ldo.js b/src/ldo.js
index 9b845e7..fa59e0b 100644
--- a/src/ldo.js
+++ b/src/ldo.js
@@ -77,6 +77,7 @@ const luaD_precall = function(L, off, nresults) {
                 luaD_hook(L, defs.LUA_HOOKCALL, -1);
             let n = f(L); /* do the actual call */
 
+            assert(typeof n == "number" && n >= 0 && n==n|0, "invalid return value from JS function (expected integer)");
             assert(n < L.top - L.ci.funcOff, "not enough elements in the stack");
 
             luaD_poscall(L, ci, L.top - n, n);
diff --git a/src/llex.js b/src/llex.js
index da15b2f..703db49 100644
--- a/src/llex.js
+++ b/src/llex.js
@@ -500,6 +500,7 @@ const llex = function(ls, seminfo) {
     ls.buff.buffer = [];
 
     for (;;) {
+        assert(typeof ls.current == "number");
         switch (ls.current) {
             case char['\n']: case char['\r']: {  /* line breaks */
                 inclinenumber(ls);
-- 
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