Skill: Crash Risk Audit

Purpose

Detects force unwraps, force casts, force try, and other crash-prone Swift patterns that can cause unrecoverable crashes during App Store review, violating Guideline 2.1.

Apple Guideline

• Primary: 2.1 — Performance: App Completeness (Crashes)
• Related: 2.1
• Reference: references/guidelines/2-performance.md

Real-World Rejection Cases

• Case: Force unwrap crash on nil response — reviewer hit edge case with test data — rejected under 2.1
  Source: Apple Developer Forums (multiple threads on crash-related rejections)
  Root cause: Force unwrap (!) causes EXC_BAD_INSTRUCTION crash at review time on edge-case data — reviewers use test accounts and synthetic data that may produce nil where the developer did not expect it

• Case: Force cast as! crash when server returned unexpected type — reviewer triggered during review
  Source: Developer blogs
  Root cause: Casting without nil check produces unrecoverable crash — reviewers will encounter this on any data type mismatch between the server and the app's model layer

Trigger

Invoke on any iOS/macOS Swift project before App Store submission to identify high-risk crash patterns.

Inputs

Name	Type	Default	Description
project_root	path	cwd	iOS/macOS project root
shared_context	object	nil	Pre-collected context from appstore-full-audit Phase 1

Actions

Phase 1: Context Collection

Skip this phase if shared_context is provided.

1. Glob **/*.swift — collect all Swift source files.
2. Glob **/*.m — collect Objective-C source files.

Phase 2: Checks

1. Force unwrap
   Run multiple Grep patterns in **/*.swift to catch all force-unwrap variants:

   • [a-zA-Z0-9_]!\.[a-zA-Z] — force unwrap before property/method access (value!.property)
   • [a-zA-Z0-9_]! — force unwrap before space (let x = value! )
   • [a-zA-Z0-9_]!, — force unwrap in argument list (foo(value!, other))
   • [a-zA-Z0-9_]!\) — force unwrap inside parentheses (foo(value!))
   • [a-zA-Z0-9_]!\] — force unwrap before subscript (arr[value!])
   • [a-zA-Z0-9_]!$ — force unwrap at end of line (let x = dict["key"]!)
     Each match that is not in a test target or a SwiftUI #Preview block → 🔴 CRITICAL per occurrence. Replace with if let, guard let, or ?? fallback.

2. Force cast
   Grep pattern as! in **/*.swift.
   Each match not in a test file → 🔴 CRITICAL. Replace with as? and appropriate nil handling.

3. Force try
   Grep pattern try! in **/*.swift.
   Each match not in a test file → 🔴 CRITICAL. Replace with do { try ... } catch { } or try?.

4. fatalError in non-exhaustive contexts
   Grep pattern fatalError\( in **/*.swift.
   For each match, Read surrounding context — if used inside a switch for enum exhaustiveness or in required init(coder:) boilerplate stubs, flag → 🟠 HIGH. Any fatalError reachable at runtime on valid user input is a crash risk.

5. UI updates on background thread
   Grep pattern DispatchQueue\.main\.async|DispatchQueue\.main\.sync in **/*.swift — check for their absence near UI updates.
   Also Grep for UILabel\.text\s*=|UIImageView\.image\s*=|tableView\.reloadData|collectionView\.reloadData — if these appear outside a DispatchQueue.main block, flag → 🟠 HIGH. Background thread UI mutations cause runtime crashes that are difficult to reproduce but may surface during review.

Phase 3: Output

Collect all findings from Phase 2 and build the prioritised findings list below. Include file paths and line numbers. Omit tiers with no findings.

Output Format

## Crash Risk Audit — Findings

### 🔴 CRITICAL — Guaranteed rejection
- [ ] TODO: Replace force unwrap with guard let or if let — crash risk on nil value — `NetworkManager.swift:45` — Guideline 2.1
- [ ] TODO: Replace `as! UserModel` with `as? UserModel` and handle nil — force cast crash risk — `FeedViewController.swift:112` — Guideline 2.1
- [ ] TODO: Replace try! with do-catch or try? — unhandled error will crash — `DatabaseManager.swift:88` — Guideline 2.1

### 🟠 HIGH — Very likely rejection
- [ ] TODO: Wrap fatalError in required init(coder:) stub with assertionFailure or a logged fallback — `CustomView.swift:22` — Guideline 2.1
- [ ] TODO: Move UILabel.text update inside DispatchQueue.main.async — UI mutation on background thread detected — `DataViewModel.swift:67`

### 🟡 MEDIUM — Possible rejection
- [ ] TODO: Audit remaining fatalError calls to verify they cannot be reached on valid user data paths

### 🟢 LOW — Best practice
- [ ] TODO: Enable Swift strict concurrency checking (SWIFT_STRICT_CONCURRENCY = complete) to catch actor-isolation violations before submission

Tools Used

Glob, Grep, Read

Constraints

• Read-only. No file edits.
• No network calls.
• Skip Phase 1 if shared_context is provided by orchestrating agent.
• Works on Swift, Objective-C, React Native, Flutter projects.

Quick Commands

Run these in your project root to check manually:

# Count force unwraps (!)
!grep -rn " as! \|try!" . --include="*.swift" | grep -v "//\|fatalError" | wc -l

# List force casts (review each one)
!grep -rn " as! " . --include="*.swift" | grep -v "//"

# Check for force try
!grep -rn "try!" . --include="*.swift" | grep -v "//"

# Check for fatalError usage
!grep -rn "fatalError\(" . --include="*.swift" | grep -v "//"

Swift Anti-Pattern Reference

examples/swift/QualityPatterns.swift

Detection Steps

1. Find target files

   • Glob: **/*.swift (exclude *Tests*, *Spec*, *Mock* paths)

2. Search for rejection patterns

   • Grep \w![.(] — force unwrap (value!.property, value!() — avoids != false positives
   • Grep \bas!\b — force cast
   • Grep \btry!\b — force try
   • Grep fatalError\|preconditionFailure — unconditional crash (flag in non-test files)
   • Grep \.reloadData()\|\.reloadSections\|beginUpdates — check surrounding context for DispatchQueue.main

3. Determine verdict

   • Force unwrap in production Swift file → 🟠 HIGH (Guideline 2.1)
   • Force cast in production Swift file → 🟠 HIGH
   • UITableView/UICollectionView reload outside DispatchQueue.main → 🔴 CRITICAL
   • fatalError reachable from normal user flow → 🟠 HIGH
   • No crash-risk patterns in production code → 🟢 pass

4. Report

   • File path + line number of each occurrence
   • Fix: Replace value! with guard let value = value else { return } or if let; wrap UI updates in DispatchQueue.main.async { }