Advanced Debugging & Swift

Debugging is one of those skills that it pays to build up over time. This talk will demonstrate debugging techniques using Swift, that are not widely known. Learn how to reuse your Swift knowledge to write lldb helpers for debugging and development.

Transcript

1. ADVANCED DEBUGGING & SWIFT
2. DAVE LEE, @KASTIGLIONE IOS @ LYFT
3. CHISEL 1 GITHUB.COM/FACEBOOK/CHISEL 1 Check out findinstances
4. ADVANCED DEBUGGING @ WWDC 2018 DEVELOPER.APPLE.COM/VIDEOS/PLAY/WWDC2018/412
5. THINS TO KEEP IN MIND > the debugger has bugs too > try something, might just work > 2 steps forward, 1 step back > pays off over time
6. CHALLENGES > Xcode provides only a subset of lldb > virtually no lldb add-on ecosystem > lldb commands don't help anything
8. command alias alias command alias
9. # ~/.lldbinit command alias alias command alias alias import command script import alias source command source alias shell platform shell ...
10. # ~/.lldbinit settings set target.language swift
11. <REFRESH>2 2 tell the people why
12. > doing more > doing less > doing different
13. ▶ CODE INJECTION TOOL
14. UNCREATIVE EXAMPLE let button = UIButton(type: .plain) button.setTitle("Tap Me", for: .normal) button.setTitleColor(.red, for: .normal) self.view.addSubview(button)
15. (lldb) expression
16. (lldb) expression
17. (lldb) call
18. let button = UIButton(type: .plain) button.setTitle("Tap Me", for: .normal) button.setTitleColor(.red, for: .normal) ▶ self.view.addSubview(button) (lldb) call print("log tap me \(button)")
19. let button = UIButton(type: .plain) button.setTitle("Tap Me", for: .normal) button.setTitleColor(.red, for: .normal) ▶ self.view.addSubview(button) (lldb) call button.setTitle("where's the adidas store?", for: .normal)
20. (lldb) thread jump --by N
21. (lldb) thread jump --by N
22. (lldb) jump +N
23. let button = UIButton(type: .plain) button.setTitle("Tap Me", for: .normal) ▶ button.setTitleColor(.red, for: .normal) self.view.addSubview(button) (lldb) jump +1
24. let button = UIButton(type: .plain) button.setTitle("Tap Me", for: .normal) ▶ if halloween && holidayThemeEnabled { button.setTitleColor(.orange, for: .normal) } else { button.setTitleColor(.red, for: .normal) } self.view.addSubview(button) (lldb) jump +1 (lldb) jump +3
25. let button = UIButton(type: .plain) button.setTitle("Tap Me", for: .normal) button.setTitleColor(.red, for: .normal) ▶ self.view.addSubview(button) (lldb) jump +1 (lldb) call self.bottomBar.addSubview(button)
26. LIVE CODING (lldb) call view.center.y = 300 (lldb) call CATransaction.flush()
27. REUSABLE HELPERS
28. PYTHON
29. NUDGE.PY SMALL EXCERPT # Fetch view.center and extract x and y member values. centerExpression = "(CGPoint)[(UIView *)%s center]" %(self.target_view.GetValue()) centerValue = target.EvaluateExpression(centerExpression, exprOptions) center_x = float(centerValue.GetChildMemberWithName('x').GetValue()) center_y = float(centerValue.GetChildMemberWithName('y').GetValue()) if self.original_center is None: self.original_center = (center_x, center_y) # Adjust the x,y center values by adding the offsets. center_x += x_offset center_y += y_offset # Set the new view.center. setExpression = "(void)[(UIView *)%s setCenter:(CGPoint){%f, %f}]" %(self.target_view.GetVal nter_x, center_y) target.EvaluateExpression(setExpression, exprOptions) # Tell CoreAnimation to flush view updates to the screen. target.EvaluateExpression("(void)[CATransaction flush]", exprOptions)
30. DISCOURAGEMENT > Helper logic written not in Swift > App code as strings > Easy to mess up, easy to give up
31. </REFRESH>
32. OLD ME | | | | | | | | | | debug | app | | | | | | | | | | | | |
33. NEW ME | | | | | | | | | | debug | app | | | | | | | | | | | | |
34. nudge, A COMMAND TO DO THIS: view.frame = view.frame.offsetBy(dx: _, dy: _) CATransaction.flush()
35. FUNCTIONS
36. func nudge(_ view: UIView, _ dx: CGFloat, _ dy: CGFloat) { view.frame = view.frame.offsetBy(dx: dx, dy: dy) CATransaction.flush() }
37. ! , BACK AT # load_swift.py import lldb @lldb.command("load_swift") def load_swift(debugger, path, ctx, result, _): with open(path) as f: contents = f.read() ctx.frame.EvaluateExpression(contents)
38. LOADING SWIFT HELPERS3 # ~/.lldbinit import ~/load_swift.py load_swift ~/helpers.swift 3 See the alias from ~/.lldbinit slide
39. (lldb) call nudge(self.view, 0, 20) error: <EXPR>:3:1: error: use of unresolved identifier 'nudge' nudge(self.view, 0, 20) ^~~~~
40. NEED $ func $nudge(_ view: UIView, _ dx: CGFloat, _ dy: CGFloat) { view.frame = view.frame.offsetBy(dx: dx, dy: dy) CATransaction.flush() }
41. (lldb) call $nudge(self.view, 0, 20)
42. EXTENSIONS
43. NO $ NEEDED extension UIView { func nudge(_ dx: CGFloat, _ dy: CGFloat) { self.frame = self.frame.offsetBy(dx: dx, dy: dy) CATransaction.flush() } }
44. (lldb) call self.view.nudge(0, 20)
45. COMPARE (lldb) call self.view.nudge(0, 20) (lldb) nudge 0 20 self.view
46. EASY TO EXTEND extension UIView { func nudge(_ dx: CGFloat, _ dy: CGFloat) { UIView.animate(withDuration: 0.2) { self.frame = self.frame.offsetBy(dx: dx, dy: dy) } CATransaction.flush() } }
47. BUILDING BLOCKS
48. extension UIView { static var root: UIView { return UIApplication.shared.keyWindow!.rootViewController!.view } }
49. (lldb) po UIView.root
50. extension UIViewController { static var current: UIViewController { var controller = UIApplication.shared.keyWindow!.rootViewController! if let child = (controller as? UINavigationController)?.topViewController { controller = child } if let child = (controller as? UITabBarController)?.selectedViewController { controller = child } return controller } }
51. (lldb) po UIViewController.current
52. extension UIView { static var current: UIView { return UIViewController.current.view } }
53. (lldb) po UIView.current
54. extension UIView { func tree() -> UnfoldSequence<UIView, [UIView]> { return sequence(state: [self]) { state in guard let view = state.popLast() else { return nil } state.append(contentsOf: view.subviews.reversed()) return view } } }
55. (lldb) po UIView.current.tree().first { $0 is UIButton } (lldb) po UIView.current.tree().filter { $0 is UIButton }
56. extension UIView { func grep(_ pattern: String) -> [UILabel] { return tree() .compactMap { $0 as? UILabel } .filter { $0.text?.range(of: pattern) != nil } } }
57. (lldb) po UIView.current.grep("message")
58. extension UIView { static func first(in root: UIView) -> Self? { return root.first { _ in true } } func first<T: UIView>(where match: (T) -> Bool) -> T? { return self.tree() .compactMap { $0 as? T } .filter(match) .first } }
59. (lldb) po UIButton.first(in: UIView.current) (lldb) po UIView.current.first { (b: UIButton) in b.currentTitle == "Tap Me" }
60. extension UIView { func fillText(_ text: String) { if let textField = UITextField.first(in: self) { textField.text = text CATransaction.flush() } } }
61. (lldb) call UIView.current.fillText("185 Berry")
62. extension UIView { func screenshot(_ path: String) { let renderer = UIGraphicsImageRenderer(bounds: self.bounds) let png = renderer.pngData { _ in self.drawHierarchy(in: self.bounds, afterScreenUpdates: false) } try! png.write(to: URL(fileURLWithPath: path)) } }
63. (lldb) call myView.screenshot("/Users/me/snap.png") (lldb) shell open /Users/me/snap.png
64. AUTOMATE STUFF YOU DO A LOT
65. (lldb) breakpoint set
66. (lldb) breakpoint set
67. (lldb) b
68. (lldb) b MyViewController.viewDidLoad Breakpoint 1: 2 locations.
69. (lldb) b 1: name = 'MyViewController.viewDidAppear', language = swift 1.1: MyApp.MyViewController.viewDidAppear(Bool) -> () at MyViewController.swift:23 1.2: @objc MyApp.MyViewController.viewDidAppear(Bool) -> () at <compiler-generated>
70. (lldb) b MyViewController.viewDidLoad (lldb) b -r ^MyApp.MyViewController.viewDidLoad
71. Is this a "shell" script? # ~/login.lldb # When the phone VC is shown, enter a phone number. b -r ^MyApp.PhoneLoginViewController.viewDidAppear action -o 'call $fillPhoneNumber("4032421999")' autocontinue # When the verify VC is shown, enter the verification. b -r ^MyApp.PhoneVerifyViewController.viewDidAppear action -o 'call $fillVerify("1234")' autocontinue # Automation setup complete, now go. continue
72. # ~/.lldbinit alias action breakpoint command add alias autocontinue breakpoint modify --auto-continue true
73. (lldb) source ~/login.lldb
74. let $touchUpInside = UIControl.Event(rawValue: 64) func $fillPhoneNumber(_ phone: String) { let textField = UITextField.first(in: UIView.current) textField.text = phone let submitButton = UIButton.first(in: UIView.current) submitButton.sendActions(for: $touchUpInside) }
75. (lldb) thread step-out
76. (lldb) thread step-out
77. (lldb) finish
78. THANKS TO PG HERVEOU for his lldb and Swift explorations.