faq.md

Frequently Asked Questions

How can I build a swift_library directly for iOS?

By default, swift_library will compile code for your host machine (e.g. macOS). As a result, you may see compiler errors if you attempt to build a swift_library which imports iOS system frameworks, such as UIKit or SwiftUI:

error: no such module 'UIKit'

In order to build a swift_library for iOS, you have two main options:

1. (Preferred) Build the swift_library transitively via an ios_* target.

The ios_* rules (e.g. ios_application, ios_framework, ios_unit_test, ios_build_test, etc.) from rules_apple apply a "transition" to their transitive dependencies which applies a number of configurations that enable them to build for the target platform.

The benefit to using these rules is that you can share a analysis and build cache with your main application, making building targets with a lot of dependencies much faster.

2. Build the swift_library directly with a config.

You can alternately create a config to build for the desired platform in your .bazelrc file:

build:ios_simulator --platforms=@build_bazel_apple_support//platforms:ios_sim_arm64

And apply it when building:

bazel build //path/to/your/library --config=ios_simulator

The drawback to this approach is that the configs will likely differ between your application and swift library, resulting in the caches not being shared.