/combine-code-review

name: combine-code-review
description: Reviews Combine framework code for memory leaks, operator misuse, and error handling. Use when reviewing code with import Combine, AnyPublisher, @Published, PassthroughSubject, or CurrentValueSubject.

Combine Code Review

Quick Reference

| Issue Type | Reference | |------------|-----------| | Publishers, Subjects, AnyPublisher | [references/publishers.md](references/publishers.md) | | map, flatMap, combineLatest, switchToLatest | [references/operators.md](references/operators.md) | | AnyCancellable, retain cycles, [weak self] | [references/memory.md](references/memory.md) | | tryMap, catch, replaceError, Never | [references/error-handling.md](references/error-handling.md) |

Review Checklist

• [ ] All `sink` closures use `[weak self]` when self owns cancellable
• [ ] No `assign(to:on:self)` usage (use `assign(to: &$property)` or sink)
• [ ] All AnyCancellables stored in Set or property (not discarded)
• [ ] Subjects exposed as `AnyPublisher` via `eraseToAnyPublisher()`
• [ ] `flatMap` used correctly (not when `map + switchToLatest` needed)
• [ ] Error handling inside `flatMap` to keep main chain alive
• [ ] `tryMap` followed by `mapError` to restore error types
• [ ] `receive(on: DispatchQueue.main)` before UI updates
• [ ] PassthroughSubject for events, CurrentValueSubject for state
• [ ] Future wrapped in Deferred when used with retry

When to Load References

• Reviewing Subjects or publisher selection → publishers.md
• Reviewing operator chains or combining publishers → operators.md
• Reviewing subscriptions or memory issues → memory.md
• Reviewing error handling or try* operators → error-handling.md

Hard gates (before you report findings)

Complete in order. Do not skip ahead while a prior gate is open.

1. **Scope** — **Pass:** You name at least one file or type under review that imports Combine or uses APIs from the Quick Reference (e.g. `AnyPublisher`, `@Published`, `PassthroughSubject`). If none apply, stop with “out of scope.” 2. **Subscription retention** — **Pass:** For each `sink`, `assign`, and `store(in:)` in scope, you state where the `AnyCancellable` is retained (property, `Set`, task lifetime) or mark **ephemeral** with a one-line reason (e.g. synchronous one-shot that cannot outlive caller). If you cannot tell from the snippet, say **unknown** and ask for surrounding storage, do not assume safe. 3. **Retain-cycle claim** — **Pass:** **Confirmed** leak findings state the capture chain (e.g. self → stored cancellable → closure strongly capturing self). Label suspected cases **risk** / **verify**, not confirmed leaks. When arguing safety, cite `[weak self]`, `[unowned self]`, or non-capturing patterns you relied on. 4. **UI / main thread** — **Pass:** For updates to UIKit/SwiftUI from a chain, you either point to `receive(on: DispatchQueue.main)`, `@MainActor`, or equivalent before the UI work, **or** flag missing scheduling with `file:line`. 5. **Severity and checklist** — **Pass:** Every **high** or **critical** item includes `file:line` (or exact pasted lines) and names which **Review Checklist** row it breaks. Lower-severity notes may omit line numbers but must still be reproducible from named files.

Review Questions

1. Are all subscriptions being retained? (Check for discarded AnyCancellables) 2. Could any sink or assign create a retain cycle with self? 3. Does flatMap need to be switchToLatest for search/autocomplete? 4. What happens when this publisher fails? (Will it kill the main chain?) 5. Are error types preserved or properly mapped after try* operators?