From 5a6ff70edcb1bed1f66539b822e0f58385ad0511 Mon Sep 17 00:00:00 2001
From: David Capello <david@igarastudio.com>
Date: Mon, 10 Sep 2018 16:00:02 -0300
Subject: [PATCH] lua: include stacktrace when we access an invalid property

---
 src/app/script/luacpp.cpp | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/app/script/luacpp.cpp b/src/app/script/luacpp.cpp
index f62e270df..1f1da0b91 100644
--- a/src/app/script/luacpp.cpp
+++ b/src/app/script/luacpp.cpp
@@ -10,10 +10,12 @@
 
 #include "app/script/luacpp.h"
 
+#include <cstdio>
+
 namespace app {
 namespace script {
 
-static const char* mt_index_code =
+static const char mt_index_code[] =
   "__generic_mt_index = function(t, k) "
   "  local mt = getmetatable(t) "
   "  local f = mt[k] "
@@ -21,7 +23,7 @@ static const char* mt_index_code =
   "  f = mt.__getters[k] "
   "  if f then return f(t) end "
   "  if type(t) == 'table' then return rawget(t, k) end "
-  "  error('Field '..tostring(k)..' does not exist')"
+  "  error(debug.traceback()..': Field '..tostring(k)..' does not exist')"
   "end "
   "__generic_mt_newindex = function(t, k, v) "
   "  local mt = getmetatable(t) "
@@ -30,12 +32,19 @@ static const char* mt_index_code =
   "  f = mt.__setters[k] "
   "  if f then return f(t, v) end "
   "  if type(t) == 'table' then return rawset(t, k, v) end "
-  "  error('Cannot set field '..tostring(k))"
+  "  error(debug.traceback()..': Cannot set field '..tostring(k))"
   "end";
 
 void run_mt_index_code(lua_State* L)
 {
-  luaL_dostring(L, mt_index_code);
+  if (luaL_loadbuffer(L, mt_index_code, sizeof(mt_index_code)-1, "internal") ||
+      lua_pcall(L, 0, 0, 0)) {
+    // Error case
+    std::string err;
+    const char* s = lua_tostring(L, -1);
+    if (s)
+      std::puts(s);
+  }
 }
 
 void create_mt_getters_setters(lua_State* L,