Fix memory leak caused by NSLocalizedString

[fthdgn]

I detected very high memory usage on some screens of my app. I investigated the problem and found that the problem is NSLocalizedString(_:tableName:bundle:value:comment:) calls on R.swift.

This PR replaces NSLocalizedString(_:tableName:bundle:value:comment:) calls with String.init(localized:table:bundle:locale:comment:) on supported platforms.

Benchmarks

Steps

• On Xcode 15.3, create a new iOS app (Storyboard/Swift)
• Create MyStrings.string Strings File (Legacy)
• Edit content of MyStrings.string to my_key = "My Text";
• Edit content of ViewController.swift to code below.
• Integrate R.swift with SPM according to documentation
• Modify comments on ViewController.swift and SPM package repo/commit to enable different scenarios
• Run the simulator on iPhone 15 iOS 17.4 simulator until timers stopped (30 seconds)
• Monitor the memory usage on Memory Report

import UIKit

class ViewController: UIViewController {
    private let label: UILabel = .init()

    private var timer: Timer?
    private var stopTimer: Timer?

    override func viewDidLoad() {
        super.viewDidLoad()
        label.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(label)
        label.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        label.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true

        timer = .scheduledTimer(withTimeInterval: 0.001, repeats: true, block: { [weak self] _ in
            let date = Date.now.ISO8601Format(.init(includingFractionalSeconds: true))
                        
            //let myValue = R.string.myStrings.my_key()
            
            //let myValue = NSLocalizedString("my_key", tableName: "MyStrings", comment: "")
            
            let myValue = String(localized: .init("my_key"), table: "MyStrings")
           
            self?.label.text = myValue + ": " + date
        })
        stopTimer = .scheduledTimer(withTimeInterval: 30, repeats: false, block: { [weak self] _ in
            self?.timer?.invalidate()
        })
    }
}

Results

• NSLocalizedString(_:tableName:bundle:value:comment:)
  High is 52.5 MB. It was rising steadily until the timer is stopped.

• String.init(localized:table:bundle:locale:comment:)
  High is 30.5 MB. It was 30 MB from the start to the end.

• R.string.myStrings.my_key() for mac-cain13/R.swift master 8d26021c6c71a513505e722f2cc82a6ad4f7f087
  High is 57.3 MB. It was rising steadily until the timer is stopped.

• R.string.myStrings.my_key() for fthdgn/R.swift nslocalizedstring-memory-leak 9f8f893d35f1d21e64abb8d991243099e3d5cdf0
  High is 30.4 MB. It was around 30 MB from the start to the end.

SwiftUI

import SwiftUI

struct ContentView: View {
    @State private var currentDate = Date.now
    let timer = Timer.publish(every: 0.001, on: .main, in: .common).autoconnect()
    
    var body: some View {
        VStack {
            Text("my_key", tableName: "MyStrings")
            //Text(NSLocalizedString("my_key", tableName: "MyStrings", comment: ""))
            //Text(R.string.myStrings.my_key)
            Text(currentDate.ISO8601Format(.init(includingFractionalSeconds: true)))
        }
        .padding()
        .onReceive(timer) { input in
            currentDate = input
        }
    }
}

SwiftUI has similiar results.

• Text.init(_:tableName:bundle:comment:) uses around 24 MB.
• Text(_:) with input NSLocalizedString(_:tableName:bundle:value:comment:)'s memory usage increases steadily.
• Text(_:StringResource) from R.swift on master branch behaves like NSLocalizedString and memory usage keeps increasing.
• Text(_:StringResource) from R.swift on this PR branch uses around 24 MB

[tomlokhorst]

Thanks, nice find!

Looking at the diff, it appears the default value behaviour differs from the original and the two new branches.

[fthdgn]

String.init one does not have any value parameter.
I am not sure purpose of that parameter. On my cases it unused. I will try to find a case where its value is essantial.

[fthdgn]

I found the usa case of value parameter.
It is used when a language file does not provide translation for a key.

I used String.init(localized:defaultValue:table:bundle:locale:comment:) function.