Dependency Management

Understanding Dependencies

Dependencies in Buck define the relationships between targets. When you build a target, Buck automatically builds all of its dependencies first.

Dependency Types

First-Party Dependencies

First-party dependencies are internal libraries you develop as part of your project:

App/BUCK (lines 23-37)

# This is a list of all of our first-party libraries that are depended upon
# (directly or transitively) by this application.
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",
]

Every first-party library has an associated test target. This list is used to determine what test targets to run in CI.

Third-Party Dependencies

Third-party dependencies come from external sources:

CocoaPods
Prebuilt Frameworks
Dynamic Frameworks

App/BUCK (lines 72-75)

deps = [
    "//Pods:CryptoSwift",
    "//Pods:PromiseKit",
    # ...
]

App/BUCK (lines 39-44)

prebuilt_frameworks = [
    "//PrebuiltFrameworks:AFNetworking",

    # Hack to enable project generation to work for the Carthage BUCK file
    # which otherwise only has `prebuilt_apple_framework`s.
    "//PrebuiltFrameworks:PrebuiltFrameworksProjectGeneratorHack",
]

App/BUCK (lines 46-49)

prebuilt_dynamic_frameworks = [
    # TODO: Comment out CardinalMobile for now until it supports M1 mac:
    # https://github.com/braintree/braintree_ios/issues/564
    # "//Pods:CardinalMobile", # Prebuilt dylib
]

Resource Dependencies

Resources like assets, storyboards, and strings are also dependencies:

App/BUCK (lines 77-81)

deps = [
    ":ExampleAppAssets",
    "//App/Resources:ExampleAppStringResources",
    "//App/Resources:StoryboardResources",
    # ...
]

Build Phase Dependencies

Build scripts must be added as dependencies to ensure proper execution order:

App/BUCK (lines 51-56)

# Build Phase scripts need to be added as dependencies.
# These only get executed when building with Xcode, not Buck.
build_phase_scripts = [
    ":Hello_World",
    ":Bye_World",
]

Dependency Declaration

Dependencies are declared in the deps parameter:

App/BUCK (lines 72-85)

apple_library(
    name = "ExampleAppLibrary",
    # ...
    deps = [
        "//Pods:CryptoSwift",
        "//Pods:PromiseKit",
        ":ExampleAppAssets",
        "//App/Resources:ExampleAppStringResources",
        "//App/Resources:StoryboardResources",
    ]
    + first_party_library_dependencies
    + prebuilt_dynamic_frameworks
    + build_phase_scripts,
)

You can use list concatenation to combine multiple dependency groups for cleaner organization.

Visualizing Dependencies

Buck provides powerful tools to query and visualize dependency graphs.

Basic Dependency Query

Find all dependencies of a target:

buck query "deps(//App:ExampleApp)"

Example Output

//App:ExampleApp
//App:ExampleAppBinary
//App:ExampleAppLibrary
//App:ExampleAppAssets
//Libraries/ASwiftModule:ASwiftModule
//Libraries/SwiftAndObjc:SwiftAndObjc
//Pods:CryptoSwift
//Pods:PromiseKit
//App/Resources:ExampleAppStringResources
//App/Resources:StoryboardResources
# ... and more

Reverse Dependencies

Find all targets that depend on a specific target:

buck query "rdeps(//App:..., //Libraries/ASwiftModule:ASwiftModule)"

This shows which targets in the //App cell depend on ASwiftModule.

Dependency Path

Find the path between two targets:

buck query "somepath(//App:ExampleApp, //Libraries/ASwiftModule:ASwiftModule)"

This shows how ExampleApp depends on ASwiftModule through intermediate targets.

Dependency Graph Visualization

Generate a visual representation of the dependency graph:

# Generate dot file
buck query "deps(//App:ExampleApp)" --output-attribute buck.type --dot > deps.dot

# Convert to SVG using Graphviz
dot -Tsvg deps.dot -o deps.svg

You need to have Graphviz installed to generate visual graphs:

brew install graphviz

Filtered Queries

Query specific types of dependencies:

First-Party Only
By Rule Type
Direct Dependencies

buck query "filter('//Libraries/.*', deps(//App:ExampleApp))"

Shows only dependencies from the Libraries cell.

buck query "kind('apple_library', deps(//App:ExampleApp))"

Shows only library targets.

buck query "deps(//App:ExampleApp, 1)"

Shows only immediate dependencies (depth = 1).

Transitive Dependencies

Buck automatically resolves transitive dependencies. When a target depends on a library, it also gets access to that library’s dependencies.

Example

# Libraries/SwiftAndObjc depends on Objc1
first_party_library(
    name = "SwiftAndObjc",
    has_objective_c = True,
)

# ExampleAppLibrary depends on SwiftAndObjc
# It automatically gets Objc1 as a transitive dependency
apple_library(
    name = "ExampleAppLibrary",
    deps = [
        "//Libraries/SwiftAndObjc:SwiftAndObjc",
    ],
)

Buck builds dependencies in the correct order automatically, so you never need to worry about build order.

Dependency Best Practices

Keep Dependencies Minimal

Only include dependencies that are actually needed. Excessive dependencies slow down builds and increase binary size.

Use Visibility Constraints

apple_library(
    name = "InternalHelper",
    visibility = ["//App:"],  # Only visible to App package
    # ...
)

Prevents accidental dependencies from other parts of the codebase.

Organize Dependencies by Type

deps = [
    # Third-party
    "//Pods:CryptoSwift",
    "//Pods:PromiseKit",
    
    # Resources
    ":ExampleAppAssets",
    "//App/Resources:StoryboardResources",
    
    # First-party
] + first_party_library_dependencies

Makes dependencies easier to understand and maintain.

Document Dependency Requirements

# This library requires AFNetworking for networking
# and CryptoSwift for encryption
deps = [
    "//PrebuiltFrameworks:AFNetworking",
    "//Pods:CryptoSwift",
]

Helps other developers understand why dependencies exist.

Testing Dependencies

Tests can depend on the code they’re testing:

App/BUCK (lines 349-359)

apple_test_lib(
    name = "UnitTests",
    srcs = glob([
        "UnitTests/*.swift",
    ]),
    deps = [
        ":ExampleAppLibrary",
    ]
    + prebuilt_frameworks
    + prebuilt_dynamic_frameworks,
)

Tests automatically inherit dependencies from their test targets:

App/BUCK (lines 64-71)

apple_library(
    name = "ExampleAppLibrary",
    # ...
    tests = app_tests,  # Links this library to test targets
    # ...
)

CI Test Target Optimization

BuckSample uses a special test target that bundles all tests into one:

App/BUCK (lines 128-133)

# This test bundles all unit test libraries into a single test target.
# Test targets can be slow to create in CI; creating only one can save significant time.
apple_test_all(
    name = "ExampleAppCITests",
    libraries = first_party_library_dependencies,
    additional_tests = app_tests,
    prebuilt_frameworks = prebuilt_frameworks + prebuilt_dynamic_frameworks,
)

This optimization reduces CI build time by avoiding the overhead of creating multiple test targets.

Get Started

Core Concepts

Building

Examples

Advanced

Reference

Dependency Management

Understanding Dependencies

Dependency Types

First-Party Dependencies

Third-Party Dependencies

Resource Dependencies

Build Phase Dependencies

Dependency Declaration

Visualizing Dependencies

Basic Dependency Query

Reverse Dependencies

Dependency Path

Dependency Graph Visualization

Filtered Queries

Transitive Dependencies

Dependency Best Practices

Testing Dependencies

CI Test Target Optimization

Next Steps

Configuration

Buck Basics

Build docs developers (and LLMs) love

Get Started

Core Concepts

Building

Examples

Advanced

Reference

​Understanding Dependencies

​Dependency Types

​First-Party Dependencies

​Third-Party Dependencies

​Resource Dependencies

​Build Phase Dependencies

​Dependency Declaration

​Visualizing Dependencies

​Basic Dependency Query

​Reverse Dependencies

​Dependency Path

​Dependency Graph Visualization

​Filtered Queries

​Transitive Dependencies

​Dependency Best Practices

​Testing Dependencies

​CI Test Target Optimization

​Next Steps

Configuration

Buck Basics

Build docs developers (and LLMs) love

Understanding Dependencies

Dependency Types

First-Party Dependencies

Third-Party Dependencies

Resource Dependencies

Build Phase Dependencies

Dependency Declaration

Visualizing Dependencies

Basic Dependency Query

Reverse Dependencies

Dependency Path

Dependency Graph Visualization

Filtered Queries

Transitive Dependencies

Dependency Best Practices

Testing Dependencies

CI Test Target Optimization

Next Steps