C2678 being thrown for no apparent reason to me - list

Question

I am trying to compile this project just to see how I am doing as I go along, but I still have a few more classes to implement that will inherit from Widget for different types. When I compile I keep getting C2678:
Error C2678 binary '==': no operator found which takes a left-hand
operand of type 'Widget' (or there is no acceptable conversion)
Assignment10 c:\program files (x86)\microsoft visual
studio\2017\community\vc\tools\msvc\14.11.25503\include\xutility line3107
I cant find where this error is thrown or why. Any help would be greatly appreciated. Sorry it's so sloppy, I've been messing with it a lot to try and find the problem.
#pragma once
#include <iostream>
using namespace std;
class Widget
{
public:
int idNumber;
//structors
Widget()
{
idNumber = 0;
}
Widget(int a)
{
idNumber = a;
}
~Widget();
//operations
int getId()
{
return idNumber;
}
//overload operators to compare idNumber
void operator= (Widget &rhs)
{
idNumber = rhs.idNumber;
}
};
----------------------------------------
#include "Widget.h"
#include <iostream>
using namespace std;
Widget::~Widget()
{
}
/*
bool Widget::operator< (Widget &rhs)
{
bool result;
result = idNumber < rhs.idNumber;
return result;
}*/
---------------------------------
#pragma once
#include "Widget.h"
#include <list>
#include <iostream>
using namespace std;
class Inventory
{
public:
Inventory();
Inventory(int i)
{
Widget w(i);
}
~Inventory();
//operations
//process order for shipment
void order(int widgID);
//recieve widget
void receive(int widgID);
//overlaod output operator
friend ostream& operator<<(ostream&, const Widget&);
protected:
list<Widget> onHand;
list<int> onOrder;
};
-------------------------------
#include "Inventory.h"
#include "Widget.h"
#include <iostream>
#include <list>
using namespace std;
Inventory::Inventory()
{
Widget w;
}
Inventory::~Inventory()
{
}
//recieve widget
void Inventory::receive(int widgID)
{
cout << " Recieved shipment of Widget type "
<< widgID << endl;
//find the iterator of the widget location
list<int>::iterator weNeed;
weNeed = find(onOrder.begin(), onOrder.end(), widgID);
//if end is returned, item not found
if (weNeed != onOrder.end())
{
cout << "Ship " << Widget(widgID) << " to fill back order" << endl;
onOrder.erase(weNeed);
}
else
{
onHand.push_front(Widget(widgID));
}
}
//process order
void Inventory::order(int widgID)
{
cout << " Recieved order for Widget type "
<< widgID << endl;
//find the iterator of the widget location
list<Widget>::iterator weHave;
weHave = find(onHand.begin(), onHand.end(), widgID);
//if end is returned, item not found
if (weHave != onHand.end())
{
cout << "Ship " << *weHave << endl;
onHand.erase(weHave);
}
else
{
cout << "Back order widget of type "
<< widgID << endl;
onHand.push_front(Widget(widgID));
}
}
ostream& operator<<(ostream& os, const Widget& wid)
{
os << wid.idNumber;
return os;
}