当前，您使用的是未设置的return location，因为geocoder.geocodePostalAddress(...)是异步函数。
这意味着你需要使用一个完成处理程序（例如）来返回location，当它有结果时，如下所示：

func getLocationFrom(postalCityCode: String, countryCode: String, completion: @escaping ( CLLocation?) -> Void) {
    
    let geocoder = CLGeocoder()
    var location: CLLocation?
    let address = CNMutablePostalAddress()
    address.postalCode = postalCityCode
    address.country = countryCode
    geocoder.geocodePostalAddress(address, preferredLocale: Locale.current) { (placemarks, error) in
        guard error == nil else {
            print("Error: \(error!)")
            return completion(nil)
        }
        guard let placemark = placemarks?.first else {
            print("Error: placemark is nil")
            return completion(nil)
        }
        guard let coordinate = placemark.location?.coordinate else {
            print("Error: coordinate is nil")
            return completion(nil)
        }
        location = CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
        print("\n--> Found location = \(location) \n")
        completion(location)   // <-- here
    }
}

像这样使用它：

getLocationFrom(postalCityCode: "200040", countryCode: "CN") { location in
     print("\n---> location: \(location) \n")
 }

编辑-1
为了测试和隔离问题，请在新的SwiftUI项目中尝试以下代码：

struct ContentView: View {
    @State var cityLocation = CLLocation()

    var body: some View {
        Text(cityLocation.description)
            .onAppear {
                getLocationFrom(postalCityCode: "200040", countryCode: "CN") { location in
                    print("\n---> location: \(location) \n")
                    if let theLocation = location {
                        cityLocation = theLocation
                    }                    
                }
            }
    }
    
    func getLocationFrom(postalCityCode: String, countryCode: String, completion: @escaping ( CLLocation?) -> Void) {
        
        let geocoder = CLGeocoder()
        var location: CLLocation?
        let address = CNMutablePostalAddress()
        address.postalCode = postalCityCode
        address.country = countryCode
        geocoder.geocodePostalAddress(address, preferredLocale: Locale.current) { (placemarks, error) in
            guard error == nil else {
                print("Error: \(error!)")
                return completion(nil)
            }
            guard let placemark = placemarks?.first else {
                print("Error: placemark is nil")
                return completion(nil)
            }
            guard let coordinate = placemark.location?.coordinate else {
                print("Error: coordinate is nil")
                return completion(nil)
            }
            location = CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
            print("\n--> Found location = \(location) \n")
            completion(location)
        }
    }
}