Summary
At Airbnb, the Mobile Developer Infra team has successfully integrated Buck into their mixed-language iOS project, which combines Swift and Objective-C. This integration has led to a significant improvement in Continuous Integration build times, achieving 50% faster builds and a 30% reduction in app size. The process of adapting Buck for this mixed-language environment presented numerous technical challenges, primarily related to header imports and module management, which were resolved through various updates and workarounds.
Key Points
Introduction to Buck and Its Benefits
- Buck is a build tool aimed at enhancing developer experience and optimizing mobile app build times.
- The successful integration of Buck has resulted in notable performance improvements: 50% faster CI builds and a 30% smaller app size for Airbnb's iOS app.
Building Process Overview
- The typical iOS app build process involves generating machine code (
.o
) files, creating Swift header files (*-Swift.h
), and linking them to produce the final executable. - Unlike Xcode, which builds modules as separate, dynamically-linked frameworks, Buck treats them as static libraries, providing optimizations such as reduced binary size and stripping of unused symbols.
Challenges Encountered
- The
-import-underlying-module
flag, which allows implicit imports in Swift, does not function with Buck because it lacks the framework structure generated by Xcode. - Bridging headers need to be explicitly provided to the Swift tool, leading to issues with header location and visibility.
Solutions Implemented
- Updates were made to Buck to generate header maps, enabling the swift tool to locate and import Objective-C headers correctly.
- Buck now correctly handles path issues for bridging headers in generated
*-Swift.h
files by passing proper compiler arguments. - A workaround was introduced for the
@import
directive limitation by replacing it with#import
, facilitated by a dedicated transformation script.
Building Mixed-Language Libraries and CocoaPods
- Each pod in CocoaPods is treated as an individual library with distinct build rules, using
apple_library
for source code and different rules for precompiled binaries and frameworks.
Future Development Plans
- Plans to enable Buck project file generation for Xcode to facilitate local development alongside continuous integration.
- The team aims to enhance Buck to build libraries as modules for improved interoperability and to optimize the caching mechanism for iOS.
- Further analysis will be conducted to evaluate the benefits gained from the shift from Xcode to Buck.
Conclusion
- The integration of Buck into Airbnb's mixed-language iOS project exemplifies the potential for improved efficiency and performance in mobile development, while also highlighting the challenges and solutions that arise when merging different programming languages in a single codebase.
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