Prettier Version 2 (and how to deal with large merge conflicts it may cause)

[tephenavies]

TerriaJS and TerriaMap have been using Prettier to automate code formatting since 2019 which helps us focus on writing code while Prettier takes on code formatting for us. This week we've upgraded our Prettier version to 2.7.1 and at the same time applied code formatting to many more files within the terriajs and TerriaMap repositories. This may lead to large merge conflicts the next time you merge from main if you have made changes in your fork to code that has now been reformatted. Follow the steps below to resolve these merge conflicts:

• Create a new branch for your merge: git checkout -b whatever-merge.
• Run yarn install.
• Merge the last commit before prettier into your branch: git merge pre-prettier-v2. Resolve any conflicts as usual.
• Run yarn install again (this step will help resolve conflicts in yarn.lock, and it's also needed to upgrade prettier to v2)
• Commit the merge above without running prettier (use git commit --no-verify).
• Merge the commit that ran prettier on all the source files into your branch. This is likely to cause heaps of conflicts, but because you've already merged the last commit before prettier, and because the prettier commit only changes formatting, you can safely accept your version any time there is a conflict. git merge post-prettier-v2 --strategy=ours --no-commit
• Run prettier on the result of the merge before committing it: yarn prettier
• Add changed files and commit the merged result: git commit -a.
• Merge main into your branch in order to pick up any changes in main that happened after the prettiergeddon: git merge origin/main (replace origin with correct remote). Resolve any conflicts as normal.
• Commit and push your branch.
• Open a pull request of your merge branch into the original one. It should merge cleanly.

If you're merging a branch-that-has-already-followed-this-procedure into your branch, you can follow the procedure above except that you need to use different commits instead of pre-prettier-v2 and post-prettier-v2. Look at the commits in the source branch and you should see two that look like this:

Use the commit hash of the commit that merged pre-prettier-v2 in place of pre-prettier-v2 above. Use the commit hash of the commit that merged post-prettier-v2 in place of post-prettier-v2 above.

These instructions will work for a fork of TerriaMap or a fork of terriajs as we've used the same process and tag names in both.

Having trouble? Post a comment below.