Implement the 'keywords' lua module

luprex/cpp/core/luastack.hpp

@@ -518,10 +518,8 @@ private:
     int size_;
 
 public:
-    LuaExtraArgs() {
-        index_ = 0;
-        size_ = 0;
-    }
+    LuaExtraArgs() : index_(0), size_(0) {}
+    LuaExtraArgs(int i, int s) : index_(i), size_(s) {}
 
     LuaSpecial operator[] (int n) const { return LuaSpecial(index_ + n); }
     int size() const { return size_; }
@@ -1186,7 +1184,9 @@ public:
 
     ~LuaExtStack() {
         if (!lua_isthrowing(L_)) {
-            lua_settop(L_, oldtop_);
+            if (lua_gettop(L_) > oldtop_) {
+                lua_settop(L_, oldtop_);
+            }
         }
     }
 };
@@ -1247,13 +1247,13 @@ public:
     // Fetch the value of the keyword.  If the keyword is found, then the
     // keyword is added to the [FOUND] set, the value is returned in slot,
     // and returns true.  Otherwise, sets slot to nil and returns false.
-    bool optional(LuaSlot slot, const char *kw);
+    bool optional(LuaSlot slot, std::string_view kw);
 
     // Fetch the value of the keyword.  If the keyword is found, then the
     // keyword is added to the [FOUND] set, the value is returned in slot,
     // and returns true.  Otherwise, sets slot to nil, returns false, and
     // stores an [ERROR] report in the keyword table.
-    bool required(LuaSlot slot, const char *kw);
+    bool required(LuaSlot slot, std::string_view kw);
 
     // Check if there are any errors so far.  If any error has been
     // detected, returns an error message, otherwise, returns empty