laerreal / gic

Git Interactive Cloner

GIC - Git Interactive Cloner

The tool allows to clone an existing Git repository making changes in history. The changes will took effect for the clone only.

Are there analogs?

Yes, they are:

• git-filter-branch: Uses hooks to apply changes to Git history. A hook is a shell script. You have to construct hooks so that the changes you want is made by those hooks in all relevant commit.

• The BFG Repo-Cleaner: It is at least 10-50x faster than git-filter-branch but providing less functionality.

TODO: about BFG

Tool	Approach
This tool	Change commits by hand during copying. Then resolve produced conflicts. Too hard for simple changes.
filter-branch	Write a script that makes the changes for you in all relevant commits. Writing a script to make complicated changes is equivalent to development of this tool.
BFG Repo-Cleaner	TODO

How to use it?

Clone original repository into a directory. Assume it is called origin_directory.

TODO: referencing original repository by SSH or HHTP(S) link is not implemented yet.

Call gic.py providing next information as CLI arguments.

• -d is destination folder. It will contain the cloned repository.
• -b list of SHA1 identifiers of commits to interrupt on (break points). One -b per commit. You could change those commits using git --amend, for instance.
• origin_directory as is after last CLI argument.

python ./gic.py \
    -d ~/destination/repo/directory \
    ~/source/repo/directory \
    -b f01fe3a921ec075374b461203b4ff24f5ec062c1 \
    -b 8a59687fe2bd1d577d95b77a5b5b66ddd99c7451

Note that the tool saves state into a file inside current work directory.

TODO: save state into .git directory of destination repository.

During first launch the tool analyzing the origin repository and play most actions those have to be done to clone the origin. Break points are taken into account at this stage.

Then the tool will begin to perform those actions one by one until either a break point or a conflict is met.

There are several cases:

• interruption on a break point: You asked the tool to stop right there. So, make the changes you want.
• interruption on a conflict caused by your changes: Resolve them by hand and add to index.
• interruption on a conflict like in the origin: Do not touch them. The tool will take actual changes from the origin during the next launch.
• interruption on conflicts of mixed types: handle it the same way. But, if there are conflicts of both types in one file then you have to manage them by hand. Refer to origin repository for help.

Now, launch the tool again. You may pass no arguments this time. All runtime information had been saved during previous launch.

python ./gic.py

You probably desire to use additional features.

• -m specifies main stream by SHA1 of one of its commits. This is only actual when there are several roots (initial commits without a parent). Just pass SAH1 of main root. Only main stream commits will be copied, including merge commits with non-main stream commits. Other commits will be taken as is. Break points on non-main stream commits are ignored.
• -r specifies a file to save internal state of the too after the process is finished. It is a debug option. This only takes effect for last invocations. But use it every time because you probably cannot predict which invocation is actually last.

How it works?

Given origin repository the tool analyzes it and plans the sequence of actions. Together those actions create same repository as the origin. An action corresponds to one or several commands that a user could entered using a terminal. E.g. git cherry-pick 000000 or export [email protected]. The tool allow to change actions in the sequence making them by hand. Then it watches consequent actions for conflicts allowing the user to resolve them by hand.

Most actions are implemented as invocations of git tool. But several actions change environment variables. They are implemented using os.environ. But environment variables changing can be made by hand using export shell command. Hence, it is only simplification of development.

Environment variables are used to preserve the original author and committer information (name, e-mail and date of each commit). So, if you change a commit, those date will be taken from the origin.