SwiftGen Integration — Expert Decisions

Expert decision frameworks for SwiftGen choices. Claude knows asset catalogs and localization — this skill provides judgment calls for when SwiftGen adds value and configuration trade-offs.

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Decision Trees

When SwiftGen Adds Value

Should you use SwiftGen for this project?
├─ > 20 assets/strings
│  └─ YES — Type safety prevents bugs
│     Typos caught at compile time
│
├─ < 10 assets/strings, solo developer
│  └─ MAYBE — Overhead vs. benefit
│     Quick projects may not need it
│
├─ Team project with shared assets
│  └─ YES — Consistency + discoverability
│     Autocomplete reveals available assets
│
├─ Assets change frequently
│  └─ YES — Broken references caught early
│     CI catches missing assets
│
└─ CI/CD pipeline exists
   └─ YES — Validate assets on every build
      Prevents runtime crashes

The trap: Using SwiftGen on tiny projects or for assets that rarely change. The setup overhead may exceed the benefit.

Template Selection

Which template should you use?
├─ Strings
│  ├─ Hierarchical keys (auth.login.title)
│  │  └─ structured-swift5
│  │     L10n.Auth.Login.title
│  │
│  └─ Flat keys (login_title)
│     └─ flat-swift5
│        L10n.loginTitle
│
├─ Assets (Images)
│  └─ swift5 (default)
│     Asset.Icons.home.image
│
├─ Colors
│  └─ swift5 with enumName param
│     Asset.Colors.primary.color
│
├─ Fonts
│  └─ swift5
│     FontFamily.Roboto.bold.font(size:)
│
└─ Storyboards
   └─ scenes-swift5
      StoryboardScene.Main.initialViewController()

Asset Organization Strategy

How should you organize assets?
├─ Small app (< 50 assets)
│  └─ Single Assets.xcassets
│     Feature folders inside catalog
│
├─ Medium app (50-200 assets)
│  └─ Feature-based catalogs
│     Auth.xcassets, Dashboard.xcassets
│     Multiple swiftgen inputs
│
├─ Large app / multi-module
│  └─ Per-module asset catalogs
│     Each module owns its assets
│     Module-specific SwiftGen runs
│
└─ Design system / shared assets
   └─ Separate DesignSystem.xcassets
      Shared across targets

Build Phase Strategy

When should SwiftGen run?
├─ Every build
│  └─ Run Script phase (before Compile Sources)
│     Always current, small overhead
│
├─ Only when assets change
│  └─ Input/Output files specified
│     Xcode skips if unchanged
│
├─ Manual only (CI generates)
│  └─ Commit generated files
│     No local SwiftGen needed
│     Risk: generated files out of sync
│
└─ Pre-commit hook
   └─ Lint + generate before commit
      Ensures consistency

---

NEVER Do

Configuration

NEVER hardcode paths without variables:

# ❌ Breaks in different environments
strings:
  inputs: /Users/john/Projects/MyApp/Resources/en.lproj/Localizable.strings
  outputs:
    output: /Users/john/Projects/MyApp/Generated/Strings.swift

# ✅ Use relative paths
strings:
  inputs: Resources/en.lproj/Localizable.strings
  outputs:
    output: Generated/Strings.swift

NEVER forget publicAccess for shared modules:

# ❌ Generated code is internal — can't use from other modules
xcassets:
  inputs: Resources/Assets.xcassets
  outputs:
    - templateName: swift5
      output: Generated/Assets.swift
      # Missing publicAccess!

# ✅ Add publicAccess for shared code
xcassets:
  inputs: Resources/Assets.xcassets
  outputs:
    - templateName: swift5
      output: Generated/Assets.swift
      params:
        publicAccess: true  # Accessible from other modules

Generated Code Usage

NEVER use string literals alongside SwiftGen:

// ❌ Defeats the purpose
let icon = UIImage(named: "home")  // String literal!
let title = NSLocalizedString("auth.login.title", comment: "")  // String literal!

// ✅ Use generated constants everywhere
let icon = Asset.Icons.home.image
let title = L10n.Auth.Login.title

NEVER modify generated files:

// ❌ Changes will be overwritten
// Generated/Assets.swift
enum Asset {
    enum Icons {
        static let home = ImageAsset(name: "home")

        // My custom addition  <- WILL BE DELETED ON NEXT RUN
        static let customIcon = ImageAsset(name: "custom")
    }
}

// ✅ Extend in separate file
// Extensions/Asset+Custom.swift
extension Asset.Icons {
    // Extensions survive regeneration
}

Build Phase

NEVER put SwiftGen after Compile Sources:

# ❌ Generated files don't exist when compiling
Build Phases order:
1. Compile Sources  <- Fails: Assets.swift doesn't exist!
2. Run Script (SwiftGen)

# ✅ Generate before compiling
Build Phases order:
1. Run Script (SwiftGen)  <- Generates Assets.swift
2. Compile Sources         <- Now Assets.swift exists

NEVER skip SwiftGen availability check:

# ❌ Build fails if SwiftGen not installed
swiftgen config run  # Error: command not found

# ✅ Check availability, warn instead of fail
if which swiftgen >/dev/null; then
  swiftgen config run --config "$SRCROOT/swiftgen.yml"
else
  echo "warning: SwiftGen not installed, skipping code generation"
fi

Version Control

NEVER commit generated files without good reason:

# ❌ Merge conflicts, stale files
git add Generated/Assets.swift
git add Generated/Strings.swift

# ✅ Gitignore generated files
# .gitignore
Generated/
*.generated.swift

# Exception: If CI doesn't run SwiftGen, commit generated files
# But then add pre-commit hook to keep them fresh

NEVER leave swiftgen.yml uncommitted:

# ❌ Team members can't regenerate
.gitignore
swiftgen.yml  <- WRONG!

# ✅ Commit configuration
git add swiftgen.yml
git add Resources/  # Source assets

String Keys

NEVER use inconsistent key conventions:

# ❌ Mixed conventions — confusing
"LoginTitle" = "Log In";
"login.button" = "Sign In";
"AUTH_ERROR" = "Error";

# ✅ Consistent hierarchical keys
"auth.login.title" = "Log In";
"auth.login.button" = "Sign In";
"auth.error.generic" = "Error";

---

Essential Patterns

Complete swiftgen.yml

# swiftgen.yml

## Strings (Localization)
strings:
  inputs:
    - Resources/en.lproj/Localizable.strings
  outputs:
    - templateName: structured-swift5
      output: Generated/Strings.swift
      params:
        publicAccess: true
        enumName: L10n

## Assets (Images)
xcassets:
  - inputs:
      - Resources/Assets.xcassets
    outputs:
      - templateName: swift5
        output: Generated/Assets.swift
        params:
          publicAccess: true

## Colors
colors:
  - inputs:
      - Resources/Colors.xcassets
    outputs:
      - templateName: swift5
        output: Generated/Colors.swift
        params:
          publicAccess: true
          enumName: ColorAsset

## Fonts
fonts:
  - inputs:
      - Resources/Fonts/
    outputs:
      - templateName: swift5
        output: Generated/Fonts.swift
        params:
          publicAccess: true

SwiftUI Convenience Extensions

// Extensions/SwiftGen+SwiftUI.swift

import SwiftUI

// Image extension
extension Image {
    init(asset: ImageAsset) {
        self.init(asset.name, bundle: BundleToken.bundle)
    }
}

// Color extension
extension Color {
    init(asset: ColorAsset) {
        self.init(asset.name, bundle: BundleToken.bundle)
    }
}

// Font extension
extension Font {
    static func custom(_ fontConvertible: FontConvertible, size: CGFloat) -> Font {
        fontConvertible.swiftUIFont(size: size)
    }
}

// Usage
struct ContentView: View {
    var body: some View {
        VStack {
            Image(asset: Asset.Icons.home)
                .foregroundColor(Color(asset: Asset.Colors.primary))

            Text(L10n.Home.title)
                .font(.custom(FontFamily.Roboto.bold, size: 24))
        }
    }
}

Build Phase Script

#!/bin/bash

# Xcode Build Phase: Run Script
# Move BEFORE "Compile Sources"

set -e

# Check if SwiftGen is installed
if ! which swiftgen >/dev/null; then
  echo "warning: SwiftGen not installed. Install via: brew install swiftgen"
  exit 0
fi

# Navigate to project root
cd "$SRCROOT"

# Create output directory if needed
mkdir -p Generated

# Run SwiftGen
echo "Running SwiftGen..."
swiftgen config run --config swiftgen.yml

echo "SwiftGen completed successfully"

Input Files (for incremental builds):

$(SRCROOT)/swiftgen.yml
$(SRCROOT)/Resources/Assets.xcassets
$(SRCROOT)/Resources/en.lproj/Localizable.strings
$(SRCROOT)/Resources/Colors.xcassets
$(SRCROOT)/Resources/Fonts

Output Files:

$(SRCROOT)/Generated/Assets.swift
$(SRCROOT)/Generated/Strings.swift
$(SRCROOT)/Generated/Colors.swift
$(SRCROOT)/Generated/Fonts.swift

Multi-Module Setup

# Module: DesignSystem/swiftgen.yml
xcassets:
  - inputs:
      - Sources/DesignSystem/Resources/Colors.xcassets
    outputs:
      - templateName: swift5
        output: Sources/DesignSystem/Generated/Colors.swift
        params:
          publicAccess: true  # Must be public for cross-module

# Module: Feature/swiftgen.yml
strings:
  - inputs:
      - Sources/Feature/Resources/en.lproj/Feature.strings
    outputs:
      - templateName: structured-swift5
        output: Sources/Feature/Generated/Strings.swift
        params:
          publicAccess: false  # Internal to module
          enumName: Strings

---

Quick Reference

Template Options

Asset Type	Template	Output
Images	swift5	Asset.Category.name.image
Colors	swift5	Asset.Colors.name.color
Strings	structured-swift5	L10n.Category.Subcategory.key
Strings (flat)	flat-swift5	L10n.keyName
Fonts	swift5	FontFamily.Name.weight.font(size:)
Storyboards	scenes-swift5	StoryboardScene.Name.viewController

Common Parameters

Parameter	Purpose	Example
publicAccess	Public access level	true for shared modules
enumName	Custom enum name	L10n, Asset, Colors
allValues	Include allValues array	true for debugging
preservePath	Keep folder structure	true for fonts

File Structure

Project/
├── swiftgen.yml           # Configuration (commit)
├── Resources/
│   ├── Assets.xcassets    # Images (commit)
│   ├── Colors.xcassets    # Colors (commit)
│   ├── Fonts/             # Custom fonts (commit)
│   └── en.lproj/
│       └── Localizable.strings  # Strings (commit)
└── Generated/             # Output (gitignore)
    ├── Assets.swift
    ├── Colors.swift
    ├── Fonts.swift
    └── Strings.swift

Troubleshooting

Issue	Cause	Fix
"No such module"	Generated before adding to target	Add to target membership
Build fails	Run Script after Compile	Move before Compile Sources
Stale generated code	Missing input/output files	Specify all inputs/outputs
Wrong bundle	Multi-target project	Use correct BundleToken

Red Flags

Smell	Problem	Fix
String literals for assets	Bypasses type safety	Use generated constants
Modified generated files	Changes get overwritten	Use extensions instead
Run Script after Compile	Files don't exist	Move before Compile Sources
No availability check	Build fails without SwiftGen	Add which swiftgen check
Committed generated files	Merge conflicts, staleness	Gitignore, generate on build
Missing publicAccess	Can't use across modules	Add publicAccess: true
Mixed key conventions	Inconsistent L10n structure	Use hierarchical keys