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XCHammerFAQ.md

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XCHammer Frequently Asked Questions

Why XCHammer?

Many features in Xcode rely on the fact that Xcode is both the editor and build system. Since XCHammer builds Bazel projects both Xcode and Bazel as a core design goal, it supports all of these features by default.

XCHammer generates an Xcode project from Bazel rules, which we've found to be a great way to describe an Xcode project and corresponding apps!

Since Xcode relies on the project configuration for semantic IDE features, like code completion and diagnostics, correctly setting up the Xcode configuration is a requirement. From the developers perspective, the Xcode build is functionally equivalent to the Bazel one: optimizations, files, errors, and warnings are identical.

What is XCHammer?

Please see the document, XCHammer Overview

How is XCHammer different than Tulsi?

Despite Tulsi being a core dependenecy of XCHammer, they produce very different results.

Generated Projects

Both Tulsi and XCHammer produce Xcode projects. Tulsi produces a project which contains a minimal set of sources. When Pinterest first migrated, developers were surprised to see missing types that used to be in the original project.

In addition to generating an Xcode project that calls bazel build, XCHammer can also generate a pure Xcode project. This output project builds primarily with Xcode. This makes it beneficial for building beta features before Bazel has supported a feature. Because XCHammer projects build with Xcode or Bazel, the project should contains all of the sources types, images, localization files, and assets. While this is slower to generate, many developers are willing to wait for the full result.

Additionally developers were spending a lot of time generating Xcode with projects. In later iterations XCHammer was made incremental by allowing the project to be split into many projects, focused Xcode projects, and nooping of generation.

Interface

XCHammer provides both a Bazel rule and CLI to build Xcode projects and Tulsi is a primarily a GUI and CLI application. There's a couple silly hacks that make this possible, but the authors have found this interface to integrate well with the XCHammer DSL.

The XCHammer authors appreciate and stand on the shoulders of contributions from the Tulsi team!

How is XCHammer versioned?

XCHammer aims to be compatible with the latest official version of Bazel, rules_apple and rules_swift.

For Apple based development, XCHammer depends on attributes of rules_apple. The current, tested, version is updated in the sample WORKSPACE.

Build System Integration

How can I build files before Xcode's build system runs?

In Xcode build target schemes, XCHammer runs Bazel before compilation to create generated resources (header maps, source files, custom genrules, etc).

It utilizes the tag feature in Bazel Bazel to determine what builds. Rules tagged xchammer are queried for at generation time, and built at build time.

To keep generation time fast, XCHammer does the minimum amount of work at generation time. Source files will show up as missing (red), but will be populated after the first Bazel build..

Development

How can I develop and debug XCHammer?

The Makefile contains commands for development and distribution. make run and make run_force_bazel both run the sample app with a debug build.

The sample is a great way to do development on, and the authors recommend adding examples of edge cases and bugs here :). Pull requests welcome!

XCHammer local repository integration

When pulling in XCHammer with git_repository and building it in tree, simply override it with a local repository in the iOS repo's build or .bazelrc

build --override_repository=xchammer=/path/to/xchammer/

XCHammer binary WORKSPACE integration for development

For binary integration / out of tree builds, make xchammer_dev_repo allows a WORKSPACE to consume XCHammer built out of tree but point to the latest build, symlinked in bazel-out. Add to the repository in question:

build \
    --override_repository=xchammer=/path/to/xchammer/bazel-out/darwin_x86_64-dbg/bin/xchammer_dev_repo

This makes it easy and pain free to build XCHammer outside of the repo but pull it into the WORKSPACE

Debugging XCHammer Bazel rules in Xcode

  1. In the iOS repository, override xchammer in the .bazelrc to point to the artifact or local source repository in question, for using the dev repo as mentioned above:
build \
    --override_repository=xchammer=/path/to/xchammer/bazel-out/darwin_x86_64-dbg/bin/xchammer_dev_repo

  1. In XCHammer repo, run make workspace_v2 && open workspace_v2.xcodeproj

  2. Change XCHammer Scheme to wait for executable to launch

  3. Hit the play button

  4. Trigger project gen in the iOS repository via bazel ( e.g. bazlisk build :MyProject, make xcode_focus, or whatever way you build the Xcode project)

Note: The rule xcode_project is cache invalidated so the binary doesn't run everytime you build with Bazel. This means if you want to constantaly re-run the binary you'll need to remove the outputs each time. For example, for the Bazel target //:FocusXcodeProj and project Focus.xcodeproj

rm -rf bazel-bin/Focus.xcodeproj && bazel build :FocusXcodeProj

How should I contribute to XCHammer?

Pull requests are always welcome! Please submit a PR to XCHammer's Github.

Additionally, run make run_force with any PR to reflect your changes. This command will produce a result that hardcodes paths on your machine into the project. Don't mind that. Future work will involve addressing that.

What tests need to pass before my PR is acceptable?

If you've modified any Bazel files (bzl, BUILD, ...) run make format to automatically format those to the Bazel style conventions.

Run make test to run all test cases for XCHammer.

Note: Pinterest runs on the HEAD of XCHammer. We require all XCHammer edge cases in the Pinterest Xcode projects to be exemplified on Github. In short, just make test.

How can debug the CLI of XCHammer in Xcode?

  1. Generate the Xcode project in XCHammer repo locally: run make workspace_v2 && open workspace_v2.xcodeproj

  2. Running To run XCHammer from Xcode for a given workspace, correctly setup the scheme for running. Set absolute paths to the WORKSPACE via --workspace_root, XCHammerConfig ( the first argument ), and --bazel. All 3 of these arguments are required.

1)  generate 
2)  /path/to/UrlGet/XCHammer.yml 
3)  --workspace_root /path/to/UrlGet/
4)  --bazel /path/to/bazel/binary

Misc

How can I build XCHammer with Bazel?

The canonical, tested, build system of XCHammer is make. Bazel support is currently under development.

Add the following to WORKSPACE file

load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")

git_repository(
    name = "xchammer",
    remote  = "https://github.com/pinterest/xchammer",
    tag = "0.2"
)

load("@xchammer:third_party:repositories.bzl", "xchammer_dependencies")

xchammer_dependencies()

Then, run bazel build @xchammer//:xchammer to compile from source to build a debug version.

For release builds, build with compiler optimizations including setting --compilation_mode=opt.