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BuckSample demonstrates a modular architecture with multiple first-party libraries. Each library is self-contained with its own BUCK file and follows consistent patterns.

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Available Libraries

The project includes 11 first-party libraries in the Libraries/ directory:
  • ASwiftModule - Pure Swift module
  • Cpp1 - C++ library with internal headers
  • Objc1 - Pure Objective-C library
  • ObjcAndSwift - Mixed Swift/Objective-C module
  • SecondSwiftModule - Additional Swift module
  • SwiftAndObjc - Swift library with Objective-C dependencies
  • SwiftReliesOnCXX - Swift library depending on C++ (Bugsnag)
  • SwiftWithAssets - Swift library with asset catalogs
  • SwiftWithMLModel - Swift library with Core ML model
  • SwiftWithPrecompiledDependency - Swift with prebuilt frameworks
  • YetAnotherSwiftModule - Another Swift module example

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Basic Library Structure

Each first-party library follows this directory structure: 
Libraries/
└── ASwiftModule/
    ├── BUCK
    ├── Sources/
    │   └── MySwiftClass.swift
    └── Tests/
        └── MySwiftClassTests.swift

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BUCK File Patterns

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Simple Swift Library

The most basic pattern uses the first_party_library macro: 
load("//Config:buck_rule_macros.bzl", "first_party_library")

first_party_library(
    name = "ASwiftModule",
#     deps = ["//Pods:Braintree"]
)
The first_party_library macro automatically discovers source files in the Sources/ directory and test files in the Tests/ directory.

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Objective-C Library

Objective-C libraries require the has_objective_c flag:
Libraries/Objc1/BUCK
load("//Config:buck_rule_macros.bzl", "first_party_library")

first_party_library(
    name = "Objc1",
    has_objective_c = True,
)

​
C++ Library

C++ libraries use has_cpp and can specify internal headers:
Libraries/Cpp1/BUCK
load("//Config:buck_rule_macros.bzl", "first_party_library")

first_party_library(
    name = "Cpp1",
    has_cpp = True,
    internal_headers = [
      "Sources/util.hpp",
    ]
)

​
Library with Assets

Libraries can include asset catalogs by depending on asset catalog targets: 
load("//Config:buck_rule_macros.bzl", "first_party_library")
load("//Config:buck_local.bzl", "buck_local_apple_asset_catalog")

first_party_library(
    name = "SwiftWithAssets",
    deps = [
        ":SwiftWithAssetsCatalog",
    ],
)

buck_local_apple_asset_catalog(
    name = "SwiftWithAssetsCatalog",
    visibility = ["PUBLIC"],
    dirs = ["Resources/Catalog.xcassets"],
)

​
Library with ML Model

Core ML models can be integrated using the mlmodel_resource helper:
Libraries/SwiftWithMLModel/BUCK
load("//Config:buck_rule_macros.bzl", "first_party_library", "mlmodel_resource")

first_party_library(
    name = "SwiftWithMLModel",
    mlmodel_generated_source = [
        ":MarsHabitatPricerInterface",
    ],
    deps = [
        ":MarsHabitatPricerMLModel",
    ],
)

mlmodel_resource(
    resource_source_name = "MarsHabitatPricerInterface",
    resource_dependency_name = "MarsHabitatPricerMLModel",
    model_directory = "Resources/",
    model_name = "MarsHabitatPricer"
)

​
Using Libraries as Dependencies

Libraries are referenced in the app’s BUCK file using their full target path:
App/BUCK
first_party_library_dependencies = [
    "//Libraries/ASwiftModule:ASwiftModule",
    "//Libraries/Cpp1:Cpp1",
    "//Libraries/Objc1:Objc1",
    "//Libraries/ObjcAndSwift:ObjcAndSwift",
    "//Libraries/SecondSwiftModule:SecondSwiftModule",
    "//Libraries/SwiftAndObjc:SwiftAndObjc",
    "//Libraries/SwiftReliesOnCXX:SwiftReliesOnCXX",
    "//Libraries/SwiftWithAssets:SwiftWithAssets",
    "//Libraries/SwiftWithMLModel:SwiftWithMLModel",
    "//Libraries/SwiftWithPrecompiledDependency:SwiftWithPrecompiledDependency",
    "//Libraries/YetAnotherSwiftModule:YetAnotherSwiftModule",
]

apple_library(
    name = "ExampleAppLibrary",
    deps = first_party_library_dependencies + [
        # other dependencies
    ],
)

​
Testing Libraries

Every library automatically gets a test target. Tests are discovered from the Tests/ directory: 
Libraries/ASwiftModule/
├── BUCK
├── Sources/
│   └── MySwiftClass.swift
└── Tests/
    └── MySwiftClassTests.swift  # Automatically included
The app’s CI test target bundles all library tests:
App/BUCK
apple_test_all(
    name = "ExampleAppCITests",
    libraries = first_party_library_dependencies,
    additional_tests = app_tests,
)
The first_party_library macro is defined in Config/buck_rule_macros.bzl and provides consistent defaults for all libraries including Swift version, compiler flags, and test discovery.

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