andyyhope / focus

Xcode Focus with xcodeproj()

Goal

I want to generate an Xcode project using Bazel and rules_ios's xcodeproj() rule which only imports a subset of the build graph, which is commonly known as "focusing" or a "focused project".

I'm still quite noob when it comes to build systems, compilers, etc but my thinking is that if we used compiled dynamic frameworks for the unfocused targets, we can improve build times and prevent unnecessary cascading builds.

Methodology

• Create a macro, focused_apple_framework(), which is a wrapper around apple_framework() and apple_dynamic_framework_import.
• In the implementation of that macro, we create the intended apple_framework as well as a apple_dynamic_framework_import with the same name but suffixed with *__unfocused.
  • To create the appropriate framework files for this target, I have a genrule that takes the output of the original framework and packages them in an acceptable *.framework folder to be consumed. This genrule's name is *__unfocused_builder
• To link the unfocused targets, each dep in the build graph checks against a memo to see if it should append the *__unfocused target.

Examples

Build

$ bazel build //focus:FocusApp

Generate Xcode project

$ bazel run //focus:Xcode
$ open focus/Focus.xcodeproj

Update focused targets

Update FOCUSED_FRAMEWORKS_MAP

Toggle focusing

Update IS_FOCUS_ENABLED

Issues

Broken links

The problem now is that the unfocused targets aren’t being treated the same as focused targets when it comes to generating the xcodeproj() rule.

• If a target is declared as focused, but there isn’t a direct link of focused modules in the build graph from root module (:Base) to it then Xcode doesn’t generate references to the module’s files during project generation.
• It will also cause a runtime crash because the necessary files aren’t being copied into the DerivedData/ folder.

Example

• Good: Focusing on SwiftA and ObjcB, will run without crashing and both modules will have their files generated and displayed in the Xcode project
• Bad: Focusing on ZZZ but not on ObjcA, will cause a runtime crash and ZZZ files won't appear in the generated Xcode project

Build graph

• Base
  • SwiftA (focused)
    • ObjcB (focused)
  • ObjcA
    • ZZZ (focused)