Format code using clang-format

[ThanHenderson]

This issue stands as proposal to automate code formatting throughout the OpenJ9 codebase, using a tool like clang-format.

On the OMR side, work is being done towards automated formatting using clang-format with integration into the CI pipeline. This current proposal builds off that work and a previous OMR proposal.

Both of those issues contain valuable discussions that are worth reading, and much of it applies here. Without belabouring the points made therein, here are what I believe to be benefited the most by using such a tool:

Reading

• Automated formatting produces more readable code; one knows what to expect. The selected format likely will not be anyone's favourite, but it will at least be enforced consistently.

Writing

• One need not spend time to ensure proper formatting manually. clang-format integrates well with IDEs and editors to format-on-save, and if not integrated, can be simply run from the command line, and easily integrated into a CI pipeline.

Reviewing

• An automated formatting tool reduces reviewer and author overhead by removing virtually all formatting related comments, allowing the review to focus on semantics of the proposed change, speeding up the reviewing/addressing cycle, and reducing the time-to-merge.

Goals

• Format the C/C++ codebase in its entirety, or a selected set of directories, using clang-format
• Add automation via GitHub hooks to validate code format of every commit within a PR
• Provide optional git hooks that enable automatic formatting of a git commit
• Provide instructions on setting up clang-format on the most popular code editors (VSCode, vim/nvim, emacs, eclipse, etc.)
• Minimize spending reviewer/author resources on any stylistic PR comments and allow us to focus on the semantics of the patch

This issue will serve as a forum of discussion and sharing opinion. Feel free to voice concerns, support, and suggestions.

[github-actions]

Issue Number: 20524
Status: Open
Recommended Components: comp:build, comp:vm, comp:test
Recommended Assignees: keithc-ca, adambrousseau, tajila