How to preserve git history when refactoring into multiple files

Question

I have a SCSS file that is ugly. I want to split it up into multiple other files to make it easier to work with.

If my file is,

file.scss


        

Answer 1

You'll need to make one commit involving both the old and new file(s) for git to associate them in the future.

Make a copy of the original but don't change the new files just yet:

cp file.scss file-sm.scss
cp file.scss file-md.scss
cp file.scss file-lg.scss

Make a minor temporary change to the original to have it committed along with the new ones:

echo "// refactoring: split the file" >> file.scss

Commit the changes:

git add .
git commit -m "Refactor: splitting up file.scss"

Now you can see the history of the old file when you use --follow and -C1 flags:

git log --follow file-lg.scss
git blame -C1 file-lg.scss

Clean up the "// refactoring .." comment and proceed with refactoring.

+1 for preserving history while refactoring - future developers will thank you.

Answer 2

Git has built-in rename / copy detection based on file similarity. To ensure it kicks in, first do a plain copy of file.scss to all of file-{sm,md,lg}.scss and commit these files. Then delete the unwanted portions from these files, remove file.scss, and commit again. Now e.g. a git log --follow --find-copies file-sm.scss should show file-sm.scss's history including the one of file.scss.