[For developers] How to fix merge conflicts related to style formatting

[njzjz]

In #2279, we started to format almost all of the codes, so it's possible that your PR is conflicting with the devel branch due to the new code formatting style. Here are some instructions to resolve the conflict you may encounter when merging your PR's branch with the devel branch.

We assume that origin is an alias for the https://github.com/deepmodeling/deepmd-kit git repo or its ssh variant. You can confirm that on your end by checking the output of git remote -v.

We recommend the following workflow:

• Abort any previous merge attempts in your branch: git merge --abort. If you weren't in the middle of a merge, this would fail with fatal: There is no merge to abort. It's normal, and you can safely ignore this message.
• Fetch all the commits from the repo git fetch origin
• Merge your PR branch with the commit right before the formatting commit:

git merge origin/devel-unformatted

This will import the config and deal with existing merge conflicts before formatting.

• Then, locally apply formatting to all the codes:

pip install pre-commit

• To format the code changes in your PR branch from the top-level source folder:

pre-commit run --all

• Commit black formatted changes.

git commit -am "apply code formatting"

• Merge your branch with devel:

git fetch origin devel
git merge origin/devel

This should work without code-style-related conflicts.