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tca-migration skill

safe

This skill guides you through migrating from The Composable Architecture to @Observable, accelerating code modernization and reducing Swift UI boilerplate.

npx playbooks add skill willsigmon/sigstack --skill tca-migration

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SKILL.md

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---
name: TCA Migration
description: Remove TCA (Composable Architecture) - find usage, migrate to @Observable, delete reducers
allowed-tools: Read, Edit, Grep, Glob, Bash
---

# TCA Migration

Remove The Composable Architecture from Leavn codebase.

## Find TCA Usage
```bash
grep -r "Reducer" --include="*.swift" | grep -v "Pods\|DerivedData"
grep -r "Store\|ViewStore" --include="*.swift"
grep -r "@Dependency" --include="*.swift"
grep -r "ComposableArchitecture" --include="*.swift"
```

## Migration Pattern
TCA Feature → @Observable ViewModel

**Before (TCA)**:
```swift
@Reducer struct MyFeature {
  @ObservableState struct State { var count = 0 }
  enum Action { case increment }
  var body: some ReducerOf<Self> { ... }
}
```

**After (@Observable)**:
```swift
@Observable @MainActor
class MyViewModel {
  var count = 0
  func increment() { count += 1 }
}
```

## Removal Order
1. Leaf features (no child reducers)
2. Parent features (after children migrated)
3. App-level store (last)
4. Remove TCA from Package.swift

## Audit Command
```bash
find . -name "*Feature.swift" -o -name "*Reducer.swift" | wc -l
```

Use when: TCA removal, migration tracking, @Observable conversion

Overview

This skill provides a focused workflow to remove The Composable Architecture (TCA) from a Swift codebase by finding usages, migrating features to @Observable view models, and deleting reducers and package references. It codifies a migration pattern, a safe removal order, and a set of audit commands to track progress. The goal is a repeatable, low-risk transition from TCA to Swift's @Observable models.

How this skill works

The skill scans the codebase for TCA artifacts (Reducers, Stores, ViewStores, @Dependency, ComposableArchitecture) using targeted grep commands and file searches. It prescribes a migration pattern: convert TCA feature reducers to @Observable @MainActor view model classes with state properties and action methods. It then guides a staged removal sequence from leaf features up to the app-level store, followed by removing the TCA package entry and running an audit command to verify counts.

When to use it

When removing TCA from a Swift project and replacing it with @Observable view models.
When auditing how many TCA feature files remain during a migration.
Before deleting package references to ensure no lingering usages.
When planning a staged, low-risk migration from reducers to view models.
When converting tests and integration points away from Store/ViewStore APIs.

Best practices

Migrate leaf features first so parent reducers can be simplified safely.
Convert state and side-effectful actions into view model properties and methods annotated with @MainActor.
Keep changes small and review compile errors frequently to catch missed usages.
Remove package dependencies only after a full project search returns zero TCA references.
Use the audit command to track remaining *Feature.swift and *Reducer.swift files between commits.

Example use cases

Replace a small feature reducer with an @Observable MyViewModel class and remove its store wiring.
Run the grep commands to list all Store/ViewStore usages before refactoring.
Migrate child feature files, then update parent reducers to remove child reducer composition.
Delete TCA from Package.swift and run project build when the audit count reaches zero.
Track migration progress across a team by committing after each feature migration and running the audit command.

FAQ

What exact commands help find TCA usages?

Use grep to search for Reducer, Store, ViewStore, @Dependency, and ComposableArchitecture while excluding Pods/DerivedData. Example: grep -r "Reducer" --include="*.swift" | grep -v "Pods\|DerivedData"

What does a typical migration look like?

Transform @Reducer structs with @ObservableState into @Observable @MainActor classes that expose state as properties and actions as methods. Update call sites to use the view model instead of Store/ViewStore.

How do I verify I can remove TCA from Package.swift?

Run a full project search for TCA tokens and use the audit command: find . -name "*Feature.swift" -o -name "*Reducer.swift" | wc -l. Ensure it returns zero and the project builds cleanly before removing the package.