git - Copy History of A project with submodules to existing single project

Question

I have a git project contains 10 submodules project. I migrated this project to another as a single project. (All submodules are just a folder in the new project now)

Is there anyway to migrate the history data of files in the submodules to new one?

Answer 1

For each submodule, you would need to import their history into the main Git project repository.

You have an example in the 2013 article "Integrating a submodule into the parent repository" from Lucas Jenß.

The idea is to clone the submodule repository beside the main parent one:

•
├── parent/
└── sub/

Remove the submodule declaration in the parent repo:

git submodule deinit -f -- path/to/submodule
rm -rf .git/modules/path/to/submodule
git rm -f path/to/submodule

Rewrite the sub/ repository history in order to move each element to the right path (the path/to/submodule one it was in the parent repository as a submodule)

However, Lucas is using a (now 2022) old obsolete git filter-branch command in order to move each submodule element to the path it needs to have in the parent repository:

CMD="git ls-files -s | sed \"s/${TAB}/${TAB}$TARGET_PATH\//\" | \
GIT_INDEX_FILE=\${GIT_INDEX_FILE}.new \
git update-index --index-info && mv \${GIT_INDEX_FILE}.new \${GIT_INDEX_FILE}"

It was valid (but cumbersome and not fool-proofed against corner case, like empty commits) in 2013.
These days (2022), it is achieved with git filter-repo (after installation, as it is python-based)

cd sub
git filter-repo --to-subdirectory-filter path/to/submodule
# done!

Finally, merge the sub history into the parent one:

$ git remote add sub ../sub/
$ git fetch sub
$ git merge --allow-unrelated-histories --no-commit sub/master
Automatic merge went well; stopped before committing as requested

Repeat that for all 10 submodules.
And you get one single Git project, with each submodule history preserved.