From 52b020d836952e5662dca6374f6c31b39fc4aead Mon Sep 17 00:00:00 2001
From: Alexander Bock <mail@alexanderbock.eu>
Date: Thu, 1 Apr 2021 23:37:35 +0200
Subject: [PATCH] Include strict lua file, throw error in configuration loading
 when overriding with unused variable

 - Preventing True/true bug
 - Fix issue with unused variable in configuration_helper
---
 scripts/configuration_helper.lua |  2 +-
 scripts/strict.lua               | 40 ++++++++++++++++++++++++++++++++
 src/engine/configuration.cpp     |  4 ++++
 3 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 scripts/strict.lua

diff --git a/scripts/configuration_helper.lua b/scripts/configuration_helper.lua
index 970314a89a..84dd547e75 100644
--- a/scripts/configuration_helper.lua
+++ b/scripts/configuration_helper.lua
@@ -702,7 +702,7 @@ function sgct.config.single(arg)
     )
     sgctconfiginitializeString = "sgct.config.single"
 
-    trackedSpecifier = "tracked=\"true\""
+    local trackedSpecifier = "tracked=\"true\""
 
     if (arg["tracked"] ~= nil and arg["tracked"] == false) then
         trackedSpecifier = "tracked=\"false\""
diff --git a/scripts/strict.lua b/scripts/strict.lua
new file mode 100644
index 0000000000..088ef4c62d
--- /dev/null
+++ b/scripts/strict.lua
@@ -0,0 +1,40 @@
+-- strict.lua
+-- checks uses of undeclared global variables
+-- All global variables must be 'declared' through a regular assignment
+-- (even assigning nil will do) in a main chunk before being used
+-- anywhere or assigned to inside a function.
+-- distributed under the Lua license: http://www.lua.org/license.html
+
+local getinfo, error, rawset, rawget = debug.getinfo, error, rawset, rawget
+
+local mt = getmetatable(_G)
+if mt == nil then
+  mt = {}
+  setmetatable(_G, mt)
+end
+
+mt.__declared = {}
+
+local function what ()
+  local d = getinfo(3, "S")
+  return d and d.what or "C"
+end
+
+mt.__newindex = function (t, n, v)
+  if not mt.__declared[n] then
+    local w = what()
+    if w ~= "main" and w ~= "C" then
+      error("assign to undeclared variable '"..n.."'", 2)
+    end
+    mt.__declared[n] = true
+  end
+  rawset(t, n, v)
+end
+  
+mt.__index = function (t, n)
+  if not mt.__declared[n] and what() ~= "C" then
+    error("variable '"..n.."' is not declared", 2)
+  end
+  return rawget(t, n)
+end
+
diff --git a/src/engine/configuration.cpp b/src/engine/configuration.cpp
index f063bded20..e168e90877 100644
--- a/src/engine/configuration.cpp
+++ b/src/engine/configuration.cpp
@@ -37,6 +37,7 @@ namespace {
     // We can't use ${SCRIPTS} here as that hasn't been defined by this point
     constexpr const char* InitialConfigHelper =
                                                "${BASE}/scripts/configuration_helper.lua";
+    constexpr const char* StrictLuaScript = "${BASE}/scripts/strict.lua";
 
     struct [[codegen::Dictionary(Configuration)]] Parameters {
         // The SGCT configuration file that determines the window and view frustum
@@ -649,6 +650,9 @@ Configuration loadConfigurationFromFile(const std::string& filename,
     if (FileSys.fileExists(absPath(InitialConfigHelper))) {
         ghoul::lua::runScriptFile(result.state, absPath(InitialConfigHelper));
     }
+    if (FileSys.fileExists(absPath(StrictLuaScript))) {
+        ghoul::lua::runScriptFile(result.state, absPath(StrictLuaScript));
+    }
 
     // Load the configuration file into the state
     ghoul::lua::runScriptFile(result.state, filename);