xccache

Under the Hood: Packaging as an xcframework

The steps to create an xcframework out of a collection of Swift sources are:

(1) Creating a framework slice (ex. for iOS iphone simulator - arm64-apple-ios-simulator). The result of this step is a framework bundle, ex. SwiftyBeaver.framework.
(2) Creating an xcframework out of framework slices using xcodebuild -create-xcframework.

There are some tricky actions in step (1) so that the framework bundle meets requirements in step (2). For example, in case of Swift frameworks, xcodebuild -create-xcframework requires a swiftinterface in the swiftmodule.

Creating a Framework Slice

By default, building a Swift package target (with swift build) does not produce a .framework bundle. We have to package it outselve from .o files, headers, swiftmodules, etc.

A.framework
  |-- A (binary)
  |-- Info.plist
  |
  |-- Headers /
  |-- Modules /
        |-- module.modulemap
        |-- A.swiftmodule /
              |-- arm64-apple-ios-simulator.swiftinterface
              |-- arm64-apple-ios-simulator.swiftdoc
              ...

Steps to create a framework:

(1) Run swift build --target A ... to build the target. Build artifacts are stored under .build/debug.
(2) Create the framework binary using libtool from .o files in .build/debug/A.build:
```
libtool -static -o A.framework/A .build/debug/A.build/**/*.o
```
(3) Copying swiftmodules & swiftinterfaces in .build/debug/A.build and .build/debug/Modules to A.framework/Modules.
Also, creating the modulemap module.modulemap under A.framework/Modules so that this framework is visible to ObjC code.
(4) Copying headers (if any) to A.framework/Headers.
(5) Copying the resource bundle (if any) (ex. in .build/debug/A_A.bundle) to the framework bundle.

Creating an xcframework from Framework Slices

xcodebuild -create-xcframework \
  -framework arm64-apple-ios-simulator/SwiftyBeaver.framework \
  -framework arm64-apple-ios/SwiftyBeaver.framework \
  -output SwiftyBeaver.xcframework

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