Print out a backtrace when a Lua error is raised

The backtrace is printed by using debug.traceback as error handler when
calling Lua functions. At the moment it still looks pretty ugly since
Lua is not aware of the file names of the scripts (to be fixed).

Reviewed-by: Jared Adams

2 files changed, 26 insertions, 20 deletions

diff --git a/src/scripting/lua.cpp b/src/scripting/lua.cpp
index c4c215d3..945392e1 100644
--- a/src/scripting/lua.cpp
+++ b/src/scripting/lua.cpp
@@ -1,6 +1,7 @@
 /*
  *  The Mana Server
  *  Copyright (C) 2007-2010  The Mana World Development Team
+ *  Copyright (C) 2010  The Mana Developers
  *
  *  This file is part of The Mana Server.
  *
@@ -1710,12 +1711,17 @@ LuaScript::LuaScript():
         { NULL, NULL }
     };
     luaL_register(mState, "mana", callbacks);
+    lua_pop(mState, 1);                     // pop the 'mana' table
 
     // Make script object available to callback functions.
     lua_pushlightuserdata(mState, (void *)&registryKey);
     lua_pushlightuserdata(mState, this);
     lua_settable(mState, LUA_REGISTRYINDEX);
 
-    lua_settop(mState, 0);
+    // Push the error handler to first index of the stack
+    lua_getglobal(mState, "debug");
+    lua_getfield(mState, -1, "traceback");
+    lua_remove(mState, 1);                  // remove the 'debug' table
+
     loadFile("scripts/lua/libmana.lua");
 }
diff --git a/src/scripting/luascript.cpp b/src/scripting/luascript.cpp
index 8e19cd52..922c15d0 100644
--- a/src/scripting/luascript.cpp
+++ b/src/scripting/luascript.cpp
@@ -1,6 +1,7 @@
 /*
  *  The Mana Server
  *  Copyright (C) 2007-2010  The Mana World Development Team
+ *  Copyright (C) 2010  The Mana Developers
  *
  *  This file is part of The Mana Server.
  *
@@ -63,11 +64,11 @@ void LuaScript::push(Thing *v)
 int LuaScript::execute()
 {
     assert(nbArgs >= 0);
-    int res = lua_pcall(mState, nbArgs, 1, 0);
+    int res = lua_pcall(mState, nbArgs, 1, 1);
     nbArgs = -1;
-    if (res || !(lua_isnil(mState, 1) || lua_isnumber(mState, 1)))
+    if (res || !(lua_isnil(mState, -1) || lua_isnumber(mState, -1)))
     {
-        const char *s = lua_tostring(mState, 1);
+        const char *s = lua_tostring(mState, -1);
 
         LOG_WARN("Lua Script Error" << std::endl
                  << "     Script  : " << mScriptFile << std::endl
@@ -76,7 +77,7 @@ int LuaScript::execute()
         lua_pop(mState, 1);
         return 0;
     }
-    res = lua_tointeger(mState, 1);
+    res = lua_tointeger(mState, -1);
     lua_pop(mState, 1);
     return res;
     mCurFunction = "";
@@ -85,26 +86,25 @@ int LuaScript::execute()
 void LuaScript::load(const char *prog)
 {
     int res = luaL_loadstring(mState, prog);
+    if (res)
+    {
+        switch (res) {
+        case LUA_ERRSYNTAX:
+            LOG_ERROR("Syntax error while loading Lua script: "
+                      << lua_tostring(mState, -1));
+            break;
+        case LUA_ERRMEM:
+            LOG_ERROR("Memory allocation error while loading Lua script");
+            break;
+        }
 
-    switch (res) {
-    case LUA_ERRSYNTAX:
-        LOG_ERROR("Syntax error while loading Lua script: "
-                  << lua_tostring(mState, -1));
-        return;
-    case LUA_ERRMEM:
-        LOG_ERROR("Memory allocation error while loading Lua script");
-        return;
+        lua_pop(mState, 1);
     }
-
-    // A Lua chunk is like a function, so "execute" it in order to initialize
-    // it.
-    res = lua_pcall(mState, 0, 0, 0);
-    if (res)
+    else if (lua_pcall(mState, 0, 0, 1))
     {
         LOG_ERROR("Failure while initializing Lua script: "
                   << lua_tostring(mState, -1));
-        lua_settop(mState, 0);
-        return;
+        lua_pop(mState, 1);
     }
 }