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rules_xcodeproj

repository·main·Indexed 20 days ago

https://github.com/mobilenativefoundation/rules_xcodeproj

Bazel rules to generate Xcode projects from workspace targets, allowing developers to use Xcode's indexing, debugging, and previews while maintaining Bazel as the source of truth. It includes the xcodeproj rule for project generation, top_level_target helpers for environment specification, and specialized generators like files_and_groups and pbxnativetargets for producing PBXProj partials.

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What's inside rules_xcodeproj

  1. Explore rules_xcodeproj example use cases

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    The examples/ directory contains several specialized implementations to demonstrate different capabilities of rules_xcodeproj:

    • cc: Demonstrates C/C++ usage with cc_binary, cc_library, and external cc_library targets.
    • integration: Exercises rules_apple features and rules_xcodeproj specific capabilities like multi-platform consolidated targets, Xcode Previews, and device support.
    • sanitizers: Demonstrates how to test Sanitizers in Build without Bazel (BwB) mode, ensuring they provide UI feedback similar to Build with Bazel (BwX) builds.

  2. What is CompileStub.m and how to resolve it

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    A CompileStub.m file is automatically added when a top-level target (like ios_application) shares a primary library dependency with another top-level target (like ios_unit_test). Because the library cannot be merged into both, the first target is left without source files, so a stub is added to allow Xcode to link correctly.

    How to resolve/avoid CompileStub.m:

    • For Tests: Set the first top-level target as the test_host. This allows the library to merge.
    • Refactor: Move the shared code into its own separate library, distinct from the primary libraries of the top-level targets.

  3. Customize your Xcode project with additional rules and providers

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    While the xcodeproj rule provides a functional default, you can customize the project to achieve an "ideal" state (e.g., custom schemes, specific build settings, or Run Script phases).

    Customization via Additional Rules

    You can add rules that xcodeproj depends on. These rules give the project generator control over how the project is set up. This is useful for:

    • Customizing scheme creation (number of targets, options).
    • Controlling which transitive dependencies are represented in Xcode.
    • Adding Xcode-specific build settings (e.g., for XCRemoteCache).
    • Adding IDE-only linting via Run Script build phases.

    Customization via Providers

    The xcodeproj rule uses an aspect (xcodeproj_aspect) to traverse the dependency graph. It collects information from standard Bazel providers (like CcInfo and SwiftInfo) and rules_xcodeproj providers.

    To implement custom logic, you can write rules that return rules_xcodeproj providers. This allows your custom rules to influence how the generator shapes the resulting Xcode targets.

  4. Understand the output of the compiler build settings generator

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    The compiler build settings generator produces two primary types of output used to configure Xcode targets with Bazel-managed dependencies:

    1. target_build_settings: A set of key-value pairs (like OTHER_SWIFT_FLAGS and SWIFT_COMPILATION_MODE) that are applied directly to an Xcode target. These settings include complex compiler flags (-Xcc, -I, -iquote) that point to Bazel's external repositories and output directories, ensuring the Xcode build environment matches the Bazel environment.

    2. swift_debug_settings: A list of raw compiler flags and search paths. This output is typically used for debugging or for more granular control over the Swift compiler invocation, including include paths (-I), quote include paths (-iquote), module map locations (-fmodule-map-file), and optimization/warning flags (e.g., -Os, -Wno-unused-variable).

    Both outputs rely on Bazel environment variables like $(BAZEL_OUT) and $(BAZEL_EXTERNAL) to resolve paths to dependencies correctly within the Xcode project structure.

  5. Understand the XCScheme generator output

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    The XCScheme generator produces Xcode scheme files and management property lists to integrate Bazel builds into the Xcode workflow.

    Key components of the output include:

    • generator.xcscheme: An XML-based Xcode scheme file. It contains PreActions (shell scripts) to initialize build output groups and prepare Bazel dependencies. It also configures BuildActionEntries for targets and testables, and sets up LaunchAction, TestAction, and ProfileAction with specific environment variables (like BUILD_WORKING_DIRECTORY and BUILD_WORKSPACE_DIRECTORY) and command-line arguments pointing to Bazel-generated partials.
    • xcschememanagement.plist: A property list that manages the visibility (isShown) and display order (orderHint) of various generated schemes within the Xcode IDE.

  6. Understand the `.bazelrc` loading order

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    The project uses a specific hierarchy of .bazelrc files to manage configurations. The loading order (from first to last) is:

    1. Project xcodeproj.bazelrc: Created from a template; contains default configs and project-level stubs.
    2. Workspace xcodeproj.bazelrc: Loaded conditionally by the project file; used for startup flags (e.g., --host_jvm_args) that apply only to rules_xcodeproj invocations.
    3. Workspace .bazelrc: The standard Bazel workspace configuration.
    4. Project xcodeproj_extra_flags.bazelrc: Loaded last; contains adjustments made via --@rules_xcodeproj//xcodeproj:extra_*_flags to ensure they override previous settings.

  7. What the `pbxnativetargets` generator does

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    The pbxnativetargets generator is a tool used to create partial Xcode project files (PBXProj partials) and file mapping files. It is designed to extract specific target-related data from an Xcode project.

    It produces:

    1. A PBXProj partial containing PBXNativeTarget related objects, including:
      • PBXNativeTarget
      • XCBuildConfiguration
      • XCBuildConfigurationList
      • Various build phases
    2. A file that maps PBXBuildFile identifiers to their corresponding file paths.

    Note on Target Processing: The generator can process a subset of targets. If multiple targets share the same name, they are processed in the same invocation to allow for target disambiguation (using the full label as the Xcode target name).

  8. How rules_xcodeproj works and its design goals

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    rules_xcodeproj is designed to generate Xcode projects directly from Bazel BUILD files. Its primary goal is to allow a working project to be created using only the xcodeproj rule, without requiring changes to your existing workspace or intermediary targets.

    Core Principles:

    • Minimalism: The xcodeproj rule alone should produce a buildable and runnable project.
    • Customizability: Projects can be refined using additional rules or by returning rules_xcodeproj providers from custom rules.
    • Fidelity: Xcode outputs should match bazel build outputs as closely as possible.
    • Native Experience: The generated project should feel like a standard Xcode project.
    • Single Source of Truth: All project definitions reside in BUILD files; generation is triggered via bazel run on an xcodeproj target.

  9. Compare top_level_anchor_target and top_level_build_target

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    When configuring Xcode schemes, choose between these two functions based on whether you want the main application target to be built:

    1. xcschemes.top_level_build_target: Use this when you want to build the top-level target (e.g., the App) and its associated library targets.
    2. xcschemes.top_level_anchor_target: Use this when you only want to build specific library targets that are dependencies of the top-level target, without building the top-level target itself.

  10. How PBXProj generation works via partials

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    The project.pbxproj file (referred to as PBXProj) is the core file controlling Xcode project behavior. Instead of a single monolithic generator, rules_xcodeproj uses multiple specialized generators that produce "partials." These partials are concatenated to form the final file.

    This partial-based approach provides two main benefits:

    1. Faster Generation: Only generators affected by specific changes need to re-run.
    2. Efficiency: Generators receive "raw" input, reducing Bazel analysis CPU time and memory usage.

  11. Use project-level configs for custom Bazel environments

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    If you need project-specific configurations, you can define a base config using the config attribute in your xcodeproj target. If you set config = "projectx_xcodeproj", the following configs become available for customization and will inherit from their respective rules_xcodeproj{_*} counterparts:

    • projectx_xcodeproj (inherits rules_xcodeproj)
    • projectx_xcodeproj_generator (inherits rules_xcodeproj_generator)
    • projectx_xcodeproj_indexbuild (inherits rules_xcodeproj_indexbuild)
    • projectx_xcodeproj_swiftuipreviews (inherits rules_xcodeproj_swiftuipreviews)

  12. Use the `$_GENERATOR_LABEL_` substitution variable

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    The rules_xcodeproj API supports a special substitution variable $_GENERATOR_LABEL_. This variable expands to the exact label of the generator target (e.g., @@_main~internal~rules_xcodeproj_generated//generator/xcodeproj). This is particularly useful when running aquery commands where you need to reference the internal generator target without knowing its exact name.

    # Using the substitution variable in an aquery
bazel run //:xcodeproj -- 'aquery $_GENERATOR_LABEL_'