Undefined symbol metadata accessor for __C.CallMeClass in swift::TypeMetadataTrait<CallMeClass>::getTypeMetadata() in CallMeClass.o

Using Swift
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I'm trying to create a C++ object in a C++ file and pass it as an argument to a Swift method called from C++, so Swift can call back into C++ using that object. But I get a link error:

ld: Undefined symbols:
  type metadata accessor for __C.CallMeClass, referenced from:
      swift::TypeMetadataTrait<CallMeClass>::getTypeMetadata() in CallMeClass.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)

My function in C++ to kick it all off is:

#include "CallMeClass.hpp"
#include "SwiftCPlusPlus-Swift.h"

void DoSomething() {
	CallMeClass cmc(7);
	
	auto swiftObject = SwiftCPlusPlus::SwiftClass::init(42, "Hello");
	swiftObject.doSomething(cmc);
}

and my Swift class:

import Foundation

public struct SwiftClass {
	public init(num1: Int, text: String) {
		self.num1 = num1
		self.text = text
	}
	
	public func doSomething(cmc: CallMeClass) {
		print("\(self) in Swift got \(num1), \"\(text)\"")
		
		cmc.CallBack()
	}
		
	var num1: Int
	var text: String
}

and the callback class header:

#pragma once

#include <swift/bridging>

class CallMeClass {
public:
	CallMeClass(int foo);
	CallMeClass(const CallMeClass& original);
	~CallMeClass();

	void CallBack() const;
	
protected:
	int mFoo;
};

Implementation:

#include "CallMeClass.hpp"
#include "SwiftCPlusPlus-Swift.h"
#include <iostream>

CallMeClass::CallMeClass(int foo) : mFoo(foo) {
	
}

CallMeClass::CallMeClass(const CallMeClass& original) : mFoo(original.mFoo) {
	
}

CallMeClass::~CallMeClass() {
	
}

void CallMeClass::CallBack() const {
	std::cout << "Call back!" << std::endl;
}

Bridging header:

#include "CallMeClass.hpp"

Anyone have an idea what I'm doing wrong?

PS - I found Undeclared use of identifier in generated Module-Swift file but the fix in there doesn't work for me, I'm already including the files in that order.

Update: Added bridging header and swift/bridging include.