rules_swift_previews

Bazel rules for generating SPM Package.swift files to enable SwiftUI Previews in Xcode for Bazel-built iOS projects.

Quick Start

MODULE.bazel

bazel_dep(name = "rules_swift_previews", version = "0.0.0")

BUILD.bazel

load("@rules_swift//swift:swift.bzl", "swift_library")
load("@rules_swift_previews//:defs.bzl", "SWIFT_PREVIEW_EXCLUDES", "swift_previews_package")

swift_library(
    name = "MyViews",
    srcs = glob(["*.swift"], exclude = SWIFT_PREVIEW_EXCLUDES),
    deps = [...],
)

swift_previews_package(
    name = "previews",
    lib = ":MyViews",
)

Usage

# Generate Package.swift and dependency files
bazel run //path/to/views:previews

# Open in Xcode for previews
open path/to/views/

SwiftResources Integration

If you use rules_swift_resources for type-safe resource access, resource modules (swift_resources_library) are automatically detected and included in the generated Package.swift. No additional configuration needed.

Generated Structure

Views/
├── Package.swift              # Generated
├── YourView.swift             # Your source files (untouched)
├── BUILD.bazel
└── .deps/                     # Generated
    ├── ModuleA/
    ├── ModuleB/
    └── ResourceModule/
        ├── Resources/
        └── ResourceModule.swift

API Reference

swift_previews_package

Attribute	Type	Default	Description
name	string	required	Target name (typically "previews")
lib	label	required	The swift_library target
ios_version	string	"18"	iOS deployment target
macos_version	string	""	macOS deployment target (empty to omit)
tvos_version	string	""	tvOS deployment target (empty to omit)
watchos_version	string	""	watchOS deployment target (empty to omit)
visionos_version	string	""	visionOS deployment target (empty to omit)

SWIFT_PREVIEW_EXCLUDES

Glob patterns to exclude from swift_library sources:

• Package.swift - Generated file
• *+Previews.swift - Preview-only files

Examples

The examples/ directory contains working examples demonstrating different use cases.

Running an Example

Each example is a standalone Bazel workspace:

cd examples/basic

# Generate the preview package
bazel run //Views:previews

# Open in Xcode for SwiftUI Previews
open Views/Package.swift

In Xcode, open the Swift file and the preview canvas will render your SwiftUI views.

Available Examples

Example	Description
basic	Minimal single-module example
multi_level_deps	Transitive dependencies: Views -> Theme -> DesignSystem
swift_resources_deps	swift_resources_library integration with bundled resources