What is Buck? Buck is a fast build system that encourages the creation of small, reusable modules consisting of code and resources. It was designed to build multiple deliverables from a single repository and is optimized for building for multiple platforms.
Core Concepts Build Files Buck uses BUCK files (or BUCK.bzl) to define build targets. These files are written in Starlark, a Python-like configuration language.
BuckSample uses Skylark syntax for build files, as configured in .buckconfig with default_build_file_syntax = SKYLARK.
Here’s an example from the App module:
load( "//Config:configs.bzl" , "app_binary_configs" , "library_configs" , "watch_binary_configs" , "message_binary_configs" , "pretty" , "info_plist_substitutions" , "bundle_identifier" , "DEVELOPMENT_LANGUAGE" ) load( "//Config:buck_rule_macros.bzl" , "apple_lib" , "apple_test_lib" , "apple_test_all" ) load( "//Config:buck_local.bzl" , "buck_local_apple_asset_catalog" , "buck_local_binary" , "buck_local_bundle" , "buck_local_workspace" )
Rules Rules are functions that define how to build a particular type of output. Buck provides built-in rules for different platforms and languages.
apple_library
apple_binary
apple_bundle
apple_resource
Defines a library target containing Swift or Objective-C code: apple_library( name = "ExampleAppLibrary" , visibility = [ "//App:" , "//App/..." , ], configs = library_configs(), swift_version = "4.0" , srcs = [ "ViewController.swift" , "AppDelegate.swift" , "LocalizationHelper.swift" , ], deps = [ "//Pods:CryptoSwift" , "//Pods:PromiseKit" , ":ExampleAppAssets" , "//App/Resources:ExampleAppStringResources" , "//App/Resources:StoryboardResources" , ] + first_party_library_dependencies, )
Defines an executable binary: apple_binary( name = "ExampleWatchAppExtensionBinary" , srcs = glob([ "WatchExtension/**/*.swift" , ]), swift_compiler_flags = [ "-target" , "i386-apple-watchos4.0-simulator" ], configs = watch_binary_configs( "ExampleApp.WatchApp.Extension" ), linker_flags = [ "-e" , "_WKExtensionMain" ], frameworks = [ "$SDKROOT/System/Library/Frameworks/CoreGraphics.framework" , "$SDKROOT/System/Library/Frameworks/Foundation.framework" , "$SDKROOT/System/Library/Frameworks/UIKit.framework" , "$SDKROOT/System/Library/Frameworks/WatchConnectivity.framework" , "$SDKROOT/System/Library/Frameworks/WatchKit.framework" , ], )
Defines an iOS app bundle: buck_local_bundle( name = "ExampleApp" , visibility = [ "//App:" , ], extension = "app" , binary = ":ExampleAppBinary" , product_name = "ExampleApp" , info_plist = "Info.plist" , info_plist_substitutions = info_plist_substitutions( "ExampleApp" ), native_xcode_deps = prebuilt_frameworks + [ ":ExampleWatchApp#watch" , ":ExampleMessageExtension" , ":ExampleWidgetExtension" , ], )
Defines resource files to be bundled: apple_resource( name = "ExampleWatchAppResources" , dirs = [], files = glob([ "WatchApplication/**/*.storyboard" ]) )
Targets A target is an instance of a rule with specific parameters. Each target has a unique name within its BUCK file.
Target names follow the pattern //path/to/package:target_name. For example, //App:ExampleApp refers to the ExampleApp target in the App/BUCK file.
Cells Cells are independent Buck packages that can reference each other. In BuckSample, the main cells include:
//App: - The main application//Libraries: - First-party library modules//Config: - Build configuration and macros//Pods: - Third-party CocoaPods dependencies//PrebuiltFrameworks: - Prebuilt framework dependencies
Macros and Custom Rules BuckSample uses custom macros to simplify common build patterns:
Libraries/ASwiftModule/BUCK
load( "//Config:buck_rule_macros.bzl" , "first_party_library" ) first_party_library( name = "ASwiftModule" , )
This first_party_library macro wraps the standard apple_library rule with common configuration.
Build Phases and Scripts Buck supports Xcode build phase scripts for pre and post-build actions:
# Defines a Build Phase script that gets executed before the "Compile Sources" step xcode_prebuild_script( name = "Hello_World" , cmd = '"$ {SRCROOT} /../scripts/sample.sh"' , inputs = [], outputs = [], ) # Defines a Build Phase script that gets executed after the "Compile Sources" step xcode_postbuild_script( name = "Bye_World" , cmd = 'echo Bye World!' , inputs = [], outputs = [], )
Build phase scripts are only executed when building with Xcode, not when building directly with Buck.
Visibility Visibility controls which other targets can depend on a given target:
apple_library( name = "ExampleAppLibrary" , visibility = [ "//App:" , "//App/..." , # Allows all targets in App and subdirectories ], # ... )
"//App:" - Only targets in the App package"//App/..." - All targets in App and its subpackages"PUBLIC" - Any target in the project["//Foo:", "//Bar:"] - Multiple specific packages Next Steps
Build Targets Learn about Buck target patterns and naming conventions
Dependencies Understand how to manage and visualize dependencies
